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Publication numberUS20020042558 A1
Publication typeApplication
Application numberUS 09/939,391
Publication dateApr 11, 2002
Filing dateAug 24, 2001
Priority dateOct 5, 2000
Also published asCA2422683A1, CA2422683C, EP1322216A1, EP1322216B1, US6801799, US20030144584, WO2002028274A1
Publication number09939391, 939391, US 2002/0042558 A1, US 2002/042558 A1, US 20020042558 A1, US 20020042558A1, US 2002042558 A1, US 2002042558A1, US-A1-20020042558, US-A1-2002042558, US2002/0042558A1, US2002/042558A1, US20020042558 A1, US20020042558A1, US2002042558 A1, US2002042558A1
InventorsYitzhak Mendelson
Original AssigneeCybro Medical Ltd.
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Pulse oximeter and method of operation
US 20020042558 A1
Abstract
A sensor for use in an optical measurement device and a method for non-invasive measurement of a blood parameter. The sensor includes sensor housing, a source of radiation coupled to the housing, and a detector assembly coupled to the housing. The source of radiation is adapted to emit radiation at predetermined frequencies. The detector assembly is adapted to detect reflected radiation at least one predetermined frequency and to generate respective signals. The signals are used to determine the parameter of the blood.
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Claims(89)
What is claimed is:
1. A sensor for use in an optical measurement device for non-invasive measurement of a blood parameter, the sensor comprising:
(a) a light source for illuminating a measurement location with incident light of at least three wavelengths, the first wavelength λ1 lying in a red (R) spectrum, and the at least second and third wavelengths λ2 and λ3 lying substantially in the infrared (IR) spectrum; and
(b) a detector assembly for detecting light returned from the illuminated location, the detector assembly being arranged so as to define a plurality of detection locations along at least one closed path around the light source.
2. A sensor as set forth in claim 1, for use in a pulse oximeter, the at least second and third wavelengths λ2 and λ3 being selected to coincide with a spectral region of the optical absorption curve, where HbO2 absorbs slightly more light than Hb, and where the extinction coefficients of Hb and HbO2 are nearly equal and remain relatively constant as a function of wavelength.
3. A sensor, as set forth in claim 2, wherein the second wavelength λ2 is in the IR spectral region around 940 nm+/−20 nm, and the third wavelength λ3 is above 700 nm.
4. A sensor, as set forth in claim 1, wherein the detector assembly comprises at least one array of detector elements arranged in a spaced-apart relationship along the at least one closed path.
5. A sensor, as set forth in claim 1, wherein the detector assembly comprises at least one ring-shaped detector element.
6. A sensor according to claim 1, wherein the plurality of the detection locations are arranged along two concentric closed paths around the light source.
7. A sensor, as set forth in claim 6, wherein the detector assembly comprises two arrays of detector elements, the detector elements of each array being arranged in a spaced apart relationship along the corresponding one of the closed paths.
8. A sensor, as set forth in claim 6, wherein the detector assembly comprises two concentric ring-shaped detector elements.
9. A sensor, as set forth in claim 1, manufactured by CMOS technology, the sensor comprising a package including said light source, and an integrated circuit plate, which comprises said at least one closed path of the detector assembly positioned around the light source, and a plurality of printed contact areas and electric conductors for mounting the light source thereon, controlling the light source, and transmitting electric signals produced by the detector assembly for further processing.
10. A sensor for use in an optical measurement device for non-invasive measurement of a blood parameter, the sensor comprising:
a light source for illuminating a measurement location with incident light of at least three wavelengths, the first wavelength λ1 lying in a red (R) spectrum, and the at least second and third wavelengths λ2 and λ3 lying substantially in the infrared (IR) spectrum; and
a detector assembly for detecting light returned from the illuminated location, the detector assembly being arranged so as to define a plurality of detection locations along two concentric closed path around the light source.
11. A pulse oximeter comprising a sensor and a control unit for operating the sensor and analyzing data generated thereby, the sensor comprising:
(a) a light source for illuminating a measurement location with incident light of at least three wavelengths, the first wavelength λ1 lying in a red (R) spectrum, and the at least second and third wavelengths λ2 and λ3 lying substantially in the infrared (IR) spectrum; and
(b) a detector assembly for detecting light returned from the illuminated location, the detector assembly being arranged so as to define a plurality of detection locations along at least one closed path around the light source.
12. A method for non-invasive determination of a blood parameter, the method comprising the steps of:
(i) illuminating a measurement location with at least three different wavelengths, a first wavelength λ1 lying in a red (R) spectrum, and at least second and third wavelengths λ2 and λ3 lying substantially in the infrared (IR) spectrum;
(ii) detecting light returned from the measurement location at different detection locations and generating data indicative of the detected light, wherein said different detection locations are arranged so as to define at least one closed path around the measurement location; and
(iii) analyzing the generated data and determining the blood parameter.
13. The method according to claim 12, wherein the analysis of the generated data comprises the steps of:
calculating data indicative of an AC/DC ratio in the light detected at each of the detection locations for the at least three wavelengths:
analyzing the calculated data and determining accepted detection locations to select corresponding AC/DC ratios for each of the at least three wavelengths, λ1, λ2 and λ3 ;and
utilizing the selected ratios for determining the blood parameter.
14. The method according to claim 13, wherein the determination of the blood parameter comprises the steps of:
calculating values of the ratio W2/W3 for the accepted detection locations in at least one closed path;
analyzing each of the calculated values to determine whether it satisfies a first predetermined condition, so as to generate a signal indicative of that a sensor position is to be adjusted, if the condition is not satisfied;
if the condition is satisfied, determining whether the quality of a photoplethysmogram is acceptable;
if the quality is acceptable, analyzing the selected ratios for calculating ratios W1/W2 and W1/W3 from the data detected in at least one closed path, and calculating the differences ABS (W1/W2 −W1/W 3); and,
analyzing the calculated differences for determining whether each of the differences satisfies a second predetermined condition for determining the blood parameter if the condition is satisfied.
15. The method according to claim 14, wherein said first predetermined condition consists of that the calculated value of W2/W3 is inside a predetermined range around the value one, said predetermined range being defined by the first threshold value, and the second predetermined condition consists of that the calculated difference ABS (W1/W2 −W1/W3) is less than certain, second threshold value.
16. A pulse oximeter for detecting a value of a parameter of blood, comprising:
a sensor housing;
a source of radiation coupled to the housing and being adapted to emit radiation at predetermined frequencies;
a detector assembly coupled to the housing and being adapted to detect reflected radiation at first, second, and third frequencies and to generate respective first, second, and third signals, wherein the first, second, and third signals are indicative of a value of the reflected radiation at the respective first, second, and third frequencies; and,
a control unit coupled to the detector assembly and adapted to receive the first, second, and third signals, to calculate first, second and third ratios of the first, second, and third signals and to responsively determine the parameter of the blood as a function of the first, second and third ratios.
17. A pulse oximeter, as set forth in claim 16, wherein the control unit is adapted to determine the parameter of the blood as a function of the first and second ratios and a calibration curve.
18. A pulse oximeter, as set forth in claim 17, wherein the calibration curve is adjusted as a function of the third ratio.
19. A pulse oximeter, as set forth in claim 16, wherein the first ratio is defined by the first signal divided by the second signal.
20. A pulse oximeter, as set forth in claim 16, wherein the second ratio is defined by the first signal divided by the third signal.
21. A pulse oximeter, as set forth in claim 16, wherein the third ratio is defined by the second signal divided by the third signal.
22. A pulse oximeter, as set forth in claim 16, wherein the first frequency is in a red frequency range, the second frequency is in a near-infrared frequency range, and the third frequency is in an infrared frequency range.
23. A pulse oximeter, as set forth in claim 22, wherein the first ratio is defined by the first signal divided by the second signal, the second ratio is defined by the first signal divided by the third signal, and the third ratio is defined by the second signal divided by the third signal.
24. A pulse oximeter, as set forth in claim 16, wherein the control unit is adapted to determine the parameter of the blood as a function of a more stable one of the first and second ratios.
25. A pulse oximeter for detecting a value of a arameter of blood, comprising:
a sensor housing;
a source of radiation coupled to the housing and being adapted to emit radiation at predetermined frequencies;
a detector assembly coupled to the housing and being adapted to detect reflected radiation at first, second, and third frequencies and to generate respective first, second, and third signals, wherein the first, second, and third signals are indicative of a value of the reflected radiation at the respective first, second, and third frequencies; and,
a control unit coupled to the detector assembly and being adapted to calculate first and second ratios of the first, second, and third signals, wherein the first ratio is defined by the first signal divided by the second signal and the second ratio is defined by the first signal divided by the third signal, and wherein the control unit is adapted to determine the parameter of the blood as a function of a more stable one of the first and second ratios.
26. A pulse oximeter, as set forth in claim 25, wherein the control unit is adapted to determine the parameter of the blood as a function of the more stable one of the first and second ratios and a calibration curve.
27. A pulse oximeter, as set forth in claim 26, wherein the calibration curve is adjusted as a function of a third ratio.
28. A pulse oximeter, as set forth in claim 27, wherein the third ratio is defined by the second signal divided by the third signal.
29. A pulse oximeter, as set forth in claim 25, wherein the first frequency is in a red frequency range, the second frequency is in a near-infrared frequency range, and the third frequency is in an infrared frequency range.
30. A pulse oximeter, as set forth in claim 25, wherein the control unit is adapted to track the first and second ratios and determine which one of the first and second ratios is more stable in real-time.
31. A pulse oximeter for detecting a value of a parameter of blood, comprising:
a sensor housing;
a source of radiation coupled to the housing and being adapted to emit radiation at predetermined frequencies; and,
a plurality of detectors coupled to the housing and being adapted to detect reflected radiation at first, second, and third frequencies and to responsively generate a plurality of first sensor signals indicative of the reflected radiation at the first frequency, a plurality of second sensor signals indicative of the reflected radiation at the second frequency, and a plurality of third sensor signals indicative of the reflected radiation at the third frequency;
a control unit being coupled to the plurality of detectors and adapted to receive the plurality of first, second and third sensor signals, to analyze the first, second and third sensor signals and determine which of the first, second and third sensor signals are valid and to generate first, second, and third frequency signals as a function of valid first sensor signals, valid second sensor signals, and valid third sensor signals, respectively and to determine the parameter of the blood as a function of the valid first, second, and third sensor signals.
32. A pulse oximeter, as set forth in claim 31, wherein the control unit is adapted to calculate first, second and third ratios of the valid first, second, and third signals and to responsively determine the parameter of the blood as a function of the first, second and third ratios.
33. A pulse oximeter, as set forth in claim 32, wherein the control unit is adapted to determine the parameter of the blood as a function of the first and second ratios and a calibration curve.
34. A pulse oximeter, as set forth in claim 33, wherein the calibration curve is adjusted as a function of the third ratio.
35. A pulse oximeter, as set forth in claim 32, wherein the first ratio is defined by the valid first signals divided by the valid second signals.
36. A pulse oximeter, as set forth in claim 32, wherein the second ratio is defined by the valid first signals divided by the valid third signals.
37. A pulse oximeter, as set forth in claim 32, wherein the third ratio is defined by the valid second signals divided by the valid third signals.
38. A pulse oximeter, as set forth in claim 31, wherein the first frequency is in a red frequency range, the second frequency is in a near-infrared frequency range, and the third frequency is in an infrared frequency range.
39. A pulse oximeter, as set forth in claim 32, wherein the first ratio is defined by the valid first signals divided by the valid second signals, the second ratio is defined by the valid first signals divided by the valid third signals, and the third ratio is defined by the valid second signals divided by the valid third signals.
40. A pulse oximeter, as set forth in claim 32, wherein the control unit is adapted to determine the parameter of the blood as a function of a more stable one of the first and second ratios.
41. A pulse oximeter, as set forth in claim 31, wherein the plurality of first, second, and third sensor signals having an AC portion and a DC portion.
42. A pulse oximeter, as set forth in claim 41, wherein a sensor signal is valid if it a ratio of the AC portion to the DC portion is within a predetermined range.
43. A pulse oximeter, as set forth in claim 42, wherein the predetermined range is 0.05 to 2.0 percent.
44. A sensor for use in an optical measurement device for non-invasive measurement of a blood parameter, comprising:
a sensor housing;
a source of radiation coupled to the housing and being adapted to emit radiation at predetermined frequencies;
a detector assembly coupled to the housing and being adapted to detect reflected radiation at least one predetermined frequency and to generate respective signals, wherein the detector assembly is ring shaped.
45. A sensor, as set forth in claim 44, wherein the detector assembly includes a plurality of detectors arranged along a closed loop path.
46. A sensor, as set forth in claim 45, wherein the closed loop path has a circular shape.
47. A sensor, as set forth in claim 45, wherein the closed loop path has an elliptical shape.
48. A sensor, as set forth in claim 45, wherein the closed loop path has a polygonal shape.
49. A sensor, as set forth in claim 44, wherein the detector assembly includes a continuous photodetector ring.
50. A sensor, as set forth in claim 49, wherein the continuous photodetector ring has a circular shape.
51. A sensor, as set forth in claim 49, wherein the continuous photo detector ring has an elliptical shape.
52. A sensor, as set forth in claim 49, wherein the continuous photo detector ring has a polygonal shape.
53. A sensor, as set forth in claim 44, wherein the detector assembly includes a first plurality of detectors arranged along an inner closed loop path and a second plurality of detectors arranged along an outer closed loop path.
54. A sensor, as set forth in claim 53, wherein the inner and outer closed loop paths have a circular shape.
55. A sensor, as set forth in claim 49, wherein the inner and outer closed loop paths have an elliptical shape.
56. A sensor, as set forth in claim 49, wherein the inner and outer closed loop paths have a polygonal shape.
57. A sensor for use in an optical measurement device for non-invasive measurement of a blood parameter, comprising:
a sensor housing;
a source of radiation coupled to the housing and being adapted to emit radiation at predetermined frequencies;
a detector assembly coupled to the housing and being adapted to detect reflected radiation at least one predetermined frequency and to generate respective signals, wherein the detector assembly includes a plurality of pairs of detectors, each pair of detectors including a near detector and a far detector.
58. A sensor, as set forth in claim 57, wherein the near detectors are arranged along an inner closed loop path and the far detectors are arranged along an outer closed loop paths.
59. A sensor, as set forth in claim 58, wherein the inner and outer closed loop paths have a circular shape.
60. A sensor, as set forth in claim 58, wherein the inner and outer closed loop paths have an elliptical shape.
61. A sensor, as set forth in claim 58, wherein the inner and outer closed loop paths have a polygonal shape.
62. A method for detecting a value of a parameter of blood using a sensor adapted to emit radiation at predetermined frequencies, to detect reflected radiation at first, second, and third frequencies and to generate respective first, second, and third signals, wherein the first, second, and third signals are indicative of a value of the reflected radiation at the respective first, second, and third frequencies, the method including the steps of:
receiving the first, second, and third signals;
calculating first, second and third ratios of the first, second, and third signals; and,
responsively determining the parameter of the blood as a function of the first, second and third ratios.
63. A method, as set forth in claim 62, wherein the parameter of the blood is determined as a function of the first and second ratios and a calibration curve.
64. A method, as set forth in claim 63, including the step of adjusting the calibration curve as a function of the third ratio.
65. A method, as set forth in claim 62, wherein the first ratio is defined by the first signal divided by the second signal.
66. A method, as set forth in claim 62, wherein the second ratio is defined by the first signal divided by the third signal.
67. A method, as set forth in claim 62, wherein the third ratio is defined by the second signal divided by the third signal.
68. A method, as set forth in claim 62, wherein the first frequency is in a red frequency range, the second frequency is in a near-infrared frequency range, and the third frequency is in an infrared frequency range.
69. A method, as set forth in claim 62, wherein the first ratio is defined by the first signal divided by the second signal, the second ratio is defined by the first signal divided by the third signal, and the third ratio is defined by the second signal divided by the third signal.
70. A method, as set forth in claim 62, including the step of determining a more stable of the first and second ratios, wherein the parameter of the blood is determined using the more stable one of the first and second ratios.
71. A method for detecting a value of a parameter of blood using a sensor adapted to emit radiation at predetermined frequencies, to detect reflected radiation at first, second, and third frequencies and to generate respective first, second, and third signals, wherein the first, second, and third signals are indicative of a value of the reflected radiation at the respective first, second, and third frequencies, the method including the steps of:
receiving the first, second and third signals;
calculate first and second ratios of the first, second and third signals, wherein the first ratio is defined by the first signal divided by the second signal and the second ratio is defined by the first signal divided by the third signal; and,
determining the parameter of the blood as a function of a more stable one of the first and second ratios.
72. A method, as set forth in claim 71, wherein the parameter of the blood as a function of the more stable one of the first and second ratios and a calibration curve.
73. A method, as set forth in claim 72, including the step of adjusted the calibration curve as a function of a third ratio.
74. A method, as set forth in claim 73, wherein the third ratio is defined by the second signal divided by the third signal.
75. A method, as set forth in claim 71, wherein the first frequency is in a red frequency range, the second frequency is in an infrared frequency range, and the third frequency is in a near-infrared frequency range.
76. A method, as set forth in claim 71, including the step of tracking the first and second ratios and determining which one of the first and second ratios is more stable in real-time.
77. A method for detecting a value of a parameter of blood using a sensor adapted to emit radiation at predetermined frequencies, to detect reflected radiation at first, second, and third frequencies and to responsively generate a plurality of first sensor signals indicative of the reflected radiation at the first frequency, a plurality of second sensor signals indicative of the reflected radiation at the second frequency, and a plurality of third sensor signals indicative of the reflected radiation at the third frequency, the method comprising:
receiving the plurality of first, second and third sensor signals;
analyzing the first, second and third sensor signals and determining which of the first, second and third sensor signals are valid;
generating first, second, and third frequency signals as a function of valid first sensor signals, valid second sensor signals, and valid third sensor signals, respectively; and,
determining the parameter of the blood as a function of the valid first, second, and third sensor signals.
78. A method, as set forth in claim 77, including the step of calculating first, second and third ratios of the first, second, and third valid signals and responsively determining the parameter of the blood as a function of the first, second and third ratios.
79. A method, as set forth in claim 78, wherein the parameter of the blood is determined as a function of the first and second ratios and a calibration curve.
80. A method, as set forth in claim 79, including the step of adjusting the calibration curve as a function of the third ratio.
81. A method, as set forth in claim 78, wherein the first ratio is defined by the valid first signals divided by the valid second signals.
82. A method, as set forth in claim 78, wherein the second ratio is defined by the valid first signals divided by the valid third signals.
83. A method, as set forth in claim 78, wherein the third ratio is defined by the valid second signals divided by the valid third signals.
84. A method, as set forth in claim 78, wherein the first frequency is in a red frequency range, the second frequency is in an infrared frequency range, and the third frequency is in a near-infrared frequency range.
85. A method, as set forth in claim 78, wherein the first ratio is defined by the valid first signals divided by the valid second signals, the second ratio is defined by the valid first signals divided by the valid third signals, and the third ratio is defined by the valid second signals divided by the valid third signals.
86. A method, as set forth in claim 78, including the step of determining the parameter of the blood as a function of a more stable one of the first and second ratios.
87. A method, as set forth in claim 77, wherein the plurality of first, second, and third sensor signals have an AC portion and a DC portion.
88. A method, as set forth in claim 87, wherein a sensor signal is valid if a ratio of the AC portion to the DC portion is within a predetermined range.
89. A method, as set forth in claim 88, wherein the predetermined range is 0.05 to 2.0 percent.
Description
    BACKGROUND OF THE INVENTION
  • [0001]
    1. Field of the Invention
  • [0002]
    This invention is generally in the field of pulse oximetry, and relates to a sensor for use in a pulse oximeter, and a method for the pulse oximeter operation.
  • [0003]
    2. Background of the Invention
  • [0004]
    Oximetry is based on spectrophotometric measurements of changes in the color of blood, enabling the non-invasive determination of oxygen saturation in the patient's blood. Generally, oximetry is based on the fact that the optical property of blood in the visible (between 500 and 700 nm) and near-infrared (between 700 and 1000 nm) spectra depends strongly on the amount of oxygen in blood.
  • [0005]
    Referring to FIG. 1, there is illustrated a hemoglobin spectra measured by oximetry based techniques. Graphs G1 and G2 correspond, respectively, to reduced hemoglobin, or deoxyhemoglobin (Hb), and oxygenated hemoglobin, or oxyhemoglobin (HbO2), spectra. As shown, deoxyhemoglobin (Hb) has a higher optical extinction (i.e., absorbs more light) in the red region of spectrum around 660 nm, as compared to that of oxyhemoglobin (HbO2). On the other hand, in the near-infrared region of the spectrum around 940 nm, the optical absorption by deoxyhemoglobin (Hb) is lower than the optical absorption of oxyhemoglobin (HbO2).
  • [0006]
    Prior art non-invasive optical sensors for measuring arterial oxyhemoglobin saturation (SaO2) by a pulse oximeter (termed SpO2) are typically comprised of a pair of small and inexpensive light emitting diodes (LEDs), and a single highly sensitive silicon photodetector. A red (R) LED centered on a peak emission wavelength around 660 nm and an infrared (IR) LED centered on a peak emission wavelength around 940 nm are used as light sources.
  • [0007]
    Pulse oximetry relies on the detection of a photoplethysmographic signal caused by variations in the quantity of arterial blood associated with periodic contraction and relaxation of a patient's heart. The magnitude of this signal depends on the amount of blood ejected from the heart into the peripheral vascular bed with each systolic cycle, the optical absorption of the blood, absorption by skin and tissue components, and the specific wavelengths that are used to illuminate the tissue. SaO2 is determined by computing the relative magnitudes of the R and IR photoplethysmograms. Electronic circuits inside the pulse oximeter separate the R and IR photoplethysmograms into their respective pulsatile (AC) and non-pulsatile (DC) signal components. An algorithm inside the pulse oximeter performs a mathematical normalization by which the time-varying AC signal at each wavelength is divided by the corresponding time-invariant DC component which results mainly from the light absorbed and scattered by the bloodless tissue, residual arterial blood when the heart is in diastole, venous blood and skin pigmentation.
  • [0008]
    Since it is assumed that the AC portion results only from the arterial blood component, this scaling process provides a normalized R/IR ratio (i.e., the ratio of AC/DC values corresponding to R- and IR-spectrum wavelengths, respectively), which is highly dependent on SaO2, but is largely independent of the volume of arterial blood entering the tissue during systole, skin pigmentation, skin thickness and vascular structure. Hence, the instrument does not need to be re-calibrated for measurements on different patients. Typical calibration of a pulse oximeter is illustrated in FIG. 2 by presenting the empirical relationship between SaO2 and the normalized R/IR ratio, which is programmed by the pulse oximeters' manufacturers.
  • [0009]
    Pulse oximeters are of two kinds operating, respectively, in transmission and reflection modes. In transmission-mode pulse oximetry, an optical sensor for measuring SaO2 is usually attached across a fingertip, foot or earlobe, such that the tissue is sandwiched between the light source and the photodetector.
  • [0010]
    In reflection-mode or backscatter type pulse oximetry, as shown in FIG. 3, the LEDs and photodetector are both mounted side-by-side next to each other on the same planar substrate. This arrangement allows for measuring SaO2 from multiple convenient locations on the body (e.g. the head, torso, or upper limbs), where conventional transmission-mode measurements are not feasible. For this reason, non-invasive reflectance pulse oximetry has recently become an important new clinical technique with potential benefits in fetal and neonatal monitoring. Using reflectance oximetry to monitor SaO2 in the fetus during labor, where the only accessible location is the fetal scalp or cheeks, or on the chest in infants with low peripheral perfusion, provides several more convenient locations for sensor attachment.
  • [0011]
    Reflection pulse oximetry, while being based on similar spectrophotometric principles as the transmission one, is more challenging to perform and has unique problems that can not always be solved by solutions suitable for solving the problems associated with the transmission-mode pulse oximetry. Generally, comparing transmission and reflection pulse oximetry, the problems associated with reflection pulse oximetry consist of the following:
  • [0012]
    In reflection pulse oximetry, the pulsatile AC signals are generally very small and, depending on sensor configuration and placement, have larger DC components as compared to those of transmission pulse oximetry. As illustrated in FIG. 4, in addition to the optical absorption and reflection due to blood, the DC signal of the R and IR photoplethysmograms in reflection pulse oximetry can be adversely affected by strong reflections from a bone. This problem becomes more apparent when applying measurements at such body locations as the forehead and the scalp, or when the sensor is mounted on the chest over the ribcage. Similarly, variations in contact pressure between the sensor and the skin can cause larger errors in reflection pulse oximetry (as compared to transmission pulse oximetry) since some of the blood near the superficial layers of the skin may be normally displaced away from the sensor housing towards deeper subcutaneous structures. Consequently, the highly reflective bloodless tissue compartment near the surface of the skin can cause large errors even at body locations where the bone is located too far away to influence the incident light generated by the sensor.
  • [0013]
    Another problem with currently available reflectance sensors is the potential for specular reflection caused by the superficial layers of the skin, when an air gap exists between the sensor and the skin, or by direct shunting of light between the LEDs and the photodetector through a thin layer of fluid which may be due to excessive sweating or from amniotic fluid present during delivery.
  • [0014]
    It is important to keep in mind the two fundamental assumptions underlying the conventional dual-wavelength pulse oximetry, which are as follows:
  • [0015]
    (1) the path of light rays with different illuminating wavelengths in tissue are substantially equal and, therefore, cancel each other, and (2) each light source illuminates the same pulsatile change in arterial blood volume.
  • [0016]
    Furthermore, the correlation between optical measurements and tissue absorptions in pulse oximetry are based on the fundamental assumption that light propagation is determined primarily by absorbance due to Lambert-Beer's law neglecting multiple scattering effects in biological tissues. In practice, however, the optical paths of different wavelengths in biological tissues is known to vary more in reflectance oximetry compared to transmission oximetry, since it strongly depends on the light scattering properties of the illuminated tissue and sensor mounting.
  • [0017]
    Several human validation studies, backed by animal investigations, have suggested that uncontrollable physiological and physical parameters can cause large variations in the calibration curve of reflectance pulse oximeters primarily at low oxygen saturation values below 70%. It was observed that the accuracy of pulse oximeters in clinical use might be adversely affected by a number of physiological parameters when measurements are made from sensors attached to the forehead, chest, or the buttock area. While the exact sources of these variations are not fully understood, it is generally believed that there are a few physiological and anatomical factors that may be the major source of these errors. It is also well known for example that changes in the ratio of blood to bloodless tissue volumes may occur through venous congestion, vasoconstriction/vasodilatation, or through mechanical pressure exerted by the sensor on the skin.
  • [0018]
    Additionally, the empirically derived calibration curve of a pulse oximeter can be altered by the effects of contact pressure exerted by the probe on the skin. This is associated with the following. The light paths in reflectance oximetry are not well defined (as compared to transmission oximetry), and thus may differ between the red and infrared wavelengths. Furthermore, the forehead and scalp areas consist of a relatively thin subcutaneous layer with the cranium bone underneath, while the tissue of other anatomical structures, such as the buttock and limbs, consists of a much thicker layer of skin and subcutaneous tissues without a nearby bony support that acts as a strong light reflector.
  • [0019]
    Several in vivo and in vitro studies have confirmed that uncontrollable physiological and physical parameters (e.g., different amounts of contact pressure applied by the sensor on the skin, variation in the ratio of bloodless tissue-to-blood content, or site-to-site variations) can often cause large errors in the oxygen saturation readings of a pulse oximeter, which are normally derived based on a single internally-programmed calibration curve. The relevant in vivo studies are disclosed in the following publications:
  • [0020]
    1. Dassel, et al., “Effect of location of the sensor on reflectance pulse oximetry”, British Journal of Obstetrics and Gynecology, vol. 104, pp. 910-916, (1997);
  • [0021]
    2. Dassel, et al., “Reflectance pulse oximetry at the forehead of newborns: The influence of varying pressure on the probe”, Journal of Clinical Monitoring, vol. 12, pp. 421-428, (1996).]
  • [0022]
    The relevant in vitro studies are disclosed, for example in the following publication:
  • [0023]
    3. Edrich et al., “Fetal pulse oximetry: influence of tissue blood content and hemoglobin concentration in a new in-vitro model”, European Journal of Obstetrics and Gynecology and Reproductive Biology, vol. 72, suppl. 1, pp. S29-S34, (1997).
  • [0024]
    Improved sensors for application in dual-wavelength reflectance pulse oximetry have been developed. As disclosed in the following publication: Mendelson, et al., “Noninvasive pulse oximetry utilizing skin reflectance photoplethysmography”, IEEE Transactions on Biomedical Engineering, vol. 35, no. 10, pp. 798-805 (1988), the total amount of backscattered light that can be detected by a reflectance sensor is directly proportional to the number of photodetectors placed around the LEDs. Additional improvements in signal-to-noise ratio were achieved by increasing the active area of the photodetector and optimizing the separation distance between the light sources and photodetectors.
  • [0025]
    Another approach is based on the use of a sensor having six photodiodes arranged symmetrically around the LEDs that is disclosed in the following publications:
  • [0026]
    4. Mendelson, et al., “Design and evaluation of a new reflectance pulse oximeter sensor”, Medical Instrumentation, vol. 22, no. 4, pp. 167-173 (1988); and
  • [0027]
    5. Mendelson, et al., “Skin reflectance pulse oximetry: in vivo measurements from the forearm and calf”, Journal of Clinical Monitoring, vol. 7, pp. 7-12, (1991).
  • [0028]
    According to this approach, in order to maximize the fraction of backscattered light collected by the sensor, the currents from all six photodiodes are summed electronically by internal circuitry in the pulse oximeter. This configuration essentially creates a large area photodetector made of six discrete photodiodes connected in parallel to produce a single current that is proportional to the amount of light backscattered from the skin. Several studies showed that this sensor configuration could be used successfully to accurately measure SaO2 from the forehead, forearm and the calf on humans. However, this sensor requires a means for heating the skin in order to increase local blood flow, which has practical limitations since it could cause skin burns.
  • [0029]
    Yet another prototype reflectance sensor is based on eight dual-wavelength LEDs and a single photodiode, and is disclosed in the following publication: Takatani et al., “Experimental and clinical evaluation of a noninvasive reflectance pulse oximeter sensor”, Journal of Clinical Monitoring, vol. 8, pp. 257-266 (1992). Here, four R and four IR LEDs are spaced at 90-degree intervals around the substrate and at an equal radial distance from the photodiode.
  • [0030]
    A similar sensor configuration based on six photodetectors mounted in the center of the sensor around the LEDs is disclosed in the following publication: Konig, et al., “Reflectance pulse oximetry—principles and obstetric application in the Zurich system”, Journal of Clinical Monitoring, vol. 14, pp. 403-412 (1998).
  • [0031]
    According to the techniques disclosed in all of the above publications, only LEDs of two wavelengths, R and IR, are used as light sources, and the computation of SaO2 is based on reflection photoplethysmograms measured by a single photodetector, regardless of whether one or multiple photodiodes chips are used to construct the sensor. This is because of the fact that the individual signals from the photodetector elements are all summed together electronically inside the pulse oximeter. Furthermore, while a radially-symmetric photodetector array can help to maximize the detection of backscattered light from the skin and minimize differences from local tissue inhomogeneity, human and animal studies confirmed that this configuration can not completely eliminate errors caused by pressure differences and site-to-site variations.
  • [0032]
    The use of a nominal dual-wavelength pair of 735/890 nm was suggested as providing the best choice for optimizing accuracy, as well as sensitivity in dual-wavelength reflectance pulse oximetry, in U.S. Pat. Nos. 5,782,237 and 5,421,329. This approach minimizes the effects of tissue heterogeneity and enables to obtain a balance in path length changes arising from perturbations in tissue absorbance. This is disclosed in the following publications.
  • [0033]
    6. Mannheimer at al., “Physio-optical considerations in the design of fetal pulse oximetry sensors”, European Journal of Obstetrics and Gynecology and Reproductive Biology, vol. 72, suppl. 1, pp. S9-S19, (1997); and
  • [0034]
    7. Mannheimer at al., “Wavelength selection for low-saturation pulse oximetry”, IEEE Transactions on Biomedical Engineering, vol. 44, no. 3, pp. 48-158 (1997)].
  • [0035]
    However, replacing the conventional R wavelength at 660 nm, which coincides with the region of the spectrum where the difference between the extinction coefficient of Hb and HbO2 is maximal, with a wavelength emitting at 735 nm, not only lowers considerably the overall sensitivity of a pulse oximeter, but does not completely eliminate errors due to sensor placement and varying contact pressures.
  • [0036]
    Pulse oximeter probes of a type comprising three or more LEDs for filtering noise and monitoring other functions, such as carboxyhemoglobin or various indicator dyes injected into the blood stream, have been developed and are disclosed, for example, in WO 00/32099 and U.S. Pat. No. 5,842,981. The techniques disclosed in these publications are aimed at providing an improved method for direct digital signal formation from input signals produced by the sensor and for filtering noise.
  • [0037]
    None of the above prior art techniques provides a solution to overcome the most essential limitation in reflectance pulse oximetry, which requires the automatic correction of the internal calibration curve from which accurate and reproducible oxygen saturation values are derived, despite variations in contact pressure or site-to-site tissue heterogeneity.
  • [0038]
    In practice, most sensors used in reflection pulse oximetry rely on closely spaced LED wavelengths in order to minimize the differences in the optical path lengths of the different wavelengths. Nevertheless, within the wavelength range required for oximetry, even closely spaced LEDs with closely spaced wavelengths mounted on the same substrate can lead to large random error in the final determination of SaO2.
  • SUMMARY OF THE INVENTION AND ADVANTAGES
  • [0039]
    The object of the invention is to provide a novel sensor design and method that functions to correct the calibration relationship of a reflectance pulse oximeter, and reduce measurement inaccuracies in general. Another object of the invention is to provide a novel sensor and method that functions to correct the calibration relationship of a reflectance pulse oximeter, and reduce measurement inaccuracies in the lower range of oxygen saturation values (typically below 70%), which is the predominant range in neonatal and fetal applications.
  • [0040]
    Yet another object of the present invention is to provide automatic correction of the internal calibration curve from which oxygen saturation is derived inside the oximeter in situations where variations in contact pressure or site-to-site tissue heterogeneity may cause large measurement inaccuracies.
  • [0041]
    Another object of the invention is to eliminate or reduce the effect of variations in the calibration of a reflectance pulse oximeter between subjects, since perturbations caused by contact pressure remain one of the major sources of errors in reflectance pulse oximetry. In fetal pulse oximetry, there are additional factors, which must be properly compensated for in order to produce an accurate and reliable measurement of oxygen saturation. For example, the fetal head is usually the presenting part, and is a rather easily accessible location for application of reflectance pulse oximetry. However, uterine contractions can cause large and unpredictable variations in the pressure exerted on the head and by the sensor on the skin, which can lead to large errors in the measurement of oxygen saturation by a dual-wavelength reflectance pulse oximeter. Another object of the invention is to provide accurate measurement of oxygen saturation in the fetus during delivery.
  • [0042]
    The basis for the errors in the oxygen saturation readings of a dual-wavelength pulse oximeter is the fact that, in practical situations, the reflectance sensor applications affect the distribution of blood in the superficial layers of the skin. This is different from an ideal situation, when a reflectance sensor measures light backscattered from a homogenous mixture of blood and bloodless tissue components. Therefore, the R and IR DC signals practically measured by photodetectors contain a relatively larger proportion of light absorbed by and reflected from the bloodless tissue compartments. In these uncontrollable practical situations, the changes caused are normally not compensated for automatically by calculating the normalized R/IR ratio since the AC portions of each photoplethysmogram, and the corresponding DC components, are affected differently by pressure or site-to-site variations. Furthermore, these changes depend not only on wavelength, but depend also on the sensor geometry, and thus cannot be eliminated completely by computing the normalized R/IR ratio, as is typically the case in dualwavelength pulse oximeters.
  • [0043]
    The inventor has found that the net result of this nonlinear effect is to cause large variations in the slope of the calibration curves. Consequently, if these variations are not compensated automatically, they will cause large errors in the final computation of SpO2, particularly at low oxygen saturation levels normally found in fetal applications.
  • [0044]
    Another object of the present invention is to compensate for these variations and to provide accurate measurement of oxygen saturation. The invention consists of, in addition to two measurement sessions typically carried out in pulse oximetry based on measurements with two wavelengths centered around the peak emission values of 660 nm (red spectrum) and 940 nm±20 nm (IR spectrum), one additional measurement session is carried out with an additional wavelength. At least one additional wavelength is preferably chosen to be substantially in the IR region of the electromagnetic spectrum, i.e., in the NIR-IR spectrum (having the peak emission value above 700 nm). In a preferred embodiment the use of at least three wavelengths enables the calculation of an at least one additional ratio formed by the combination of the two IR wavelengths, which is mostly dependent on changes in contact pressure or site-to-site variations. In a preferred embodiment, slight dependence of the ratio on variations in arterial oxygen saturation that may occur, is easily minimized or eliminated completely, by the proper selection and matching of the peak emission wavelengths and spectral characteristics of the at least two IR-light sources.
  • [0045]
    Preferably, the selection of the IR wavelengths is based on certain criteria. The IR wavelengths are selected to coincide with the region of the optical absorption curve where HbO2 absorbs slightly more light than Hb. The IR wavelengths are in the spectral regions where the extinction coefficients of both Hb and HbO2 are nearly equal and remain relatively constant as a function of wavelength, respectively.
  • [0046]
    In a preferred embodiment, tracking changes in the ratio formed by the two IR wavelengths, in real-time, permits automatic correction of errors in the normalized ratio obtained from the R-wavelength and each of the IR-wavelengths. The term “ratio” signifies the ratio of two values of AC/DC corresponding to two different wavelengths. This is similar to adding another equation to solve a problem with at least three unknowns (i.e., the relative concentrations of HbO2 and Hb, which are used to calculate SaO2, and the unknown variable fraction of blood-to-tissue volumes that effects the accurate determination of SaO2), which otherwise must rely on only two equations in the case of only two wavelengths used in conventional dual-wavelength pulse oximetry. In a preferred embodiment, a third wavelength provides the added ability to compute SaO2 based on the ratio formed from the R-wavelength and either of the IR-wavelengths. In a preferred embodiment, changes in these ratios are tracked and compared in real-time to determine which ratio produces a more stable or less noisy signal. That ratio is used predominantly for calculating SaO2.
  • [0047]
    The present invention utilizes collection of light reflected from the measurement location at different detection locations arranged along a closed path around light emitting elements, which can be LEDs or laser sources. Preferably, these detection locations are arranged in two concentric rings, the so-called “near” and “far” rings, around the light emitting elements. This arrangement enables optimal positioning of the detectors for high quality measurements, and enables discrimination between photodetectors receiving “good” information (i.e., AC and DC values which would result in accurate calculations of SpO2) and “bad” information (i.e., AC and DC values which would result in inaccurate calculations of Sp0 2).
  • [0048]
    There is thus provided according to one aspect of the present invention, a sensor for use in an optical measurement device for non-invasive measurements of blood parameters, the sensor comprising:
  • [0049]
    (1) a light source for illuminating a measurement location with incident light of at least three wavelengths, the first wavelength lying in a red (R) spectrum, and the at least second and third wavelengths lying substantially in the infrared (IR) spectrum and
  • [0050]
    (2) a detector assembly for detecting light returned from the illuminated location, the detector assembly being arranged so as to define a plurality of detection locations along at least one closed path around the light source.
  • [0051]
    The term “closed path” used herein signifies a closed curve, like a ring, ellipse, or polygon, and the like.
  • [0052]
    The detector assembly is comprised of at least one array of discrete detectors (e.g., photodiodes) accommodated along at least one closed path, or at least one continuous photodetector defining the closed path.
  • [0053]
    The term “substantially IR spectrum” used herein signifies a spectrum range including near infrared and infrared regions.
  • [0054]
    According to another aspect of the present invention, there is provided a pulse oximeter utilizing a sensor constructed as defined above, and a control unit for operating the sensor and analyzing data generated thereby.
  • [0055]
    According to yet another aspect of the present invention, there is provided a method for non-invasive determination of a blood parameter, the method comprising the steps of:
  • [0056]
    illuminating a measurement location with at least three different wavelengths λ1, λ2 and λ3, the first wavelength λ1 lying in a red (R) spectrum, and the at least second and at least third wavelengths λ2 and λ3 lying substantially in the infrared (IR) spectrum;
  • [0057]
    detecting light returned from the measurement location at different detection locations and generating data indicative of the detected light, wherein said different detection locations are arranged so as to define at least one closed path around the measurement location; and
  • [0058]
    analyzing the generated data and determining the blood parameter.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • [0059]
    Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
  • [0060]
    [0060]FIG. 1 illustrates hemoglobin spectra as measured by oximetry based techniques;
  • [0061]
    [0061]FIG. 2 illustrates a calibration curve used in pulse oximetry as typically programmed by the pulse oximeters manufacturers;
  • [0062]
    [0062]FIG. 3 illustrates the relative disposition of light source and detector in reflectionmode or backscatter type pulse oximetry;
  • [0063]
    [0063]FIG. 4 illustrates light propagation in reflection pulse oximetry;
  • [0064]
    [0064]FIGS. 5A and 5B illustrate a pulse oximeter reflectance sensor operating under ideal and practical conditions, respectively;
  • [0065]
    [0065]FIG. 6 illustrates variations of the slopes of calibration curves in reflectance pulse oximetry measurements;
  • [0066]
    [0066]FIG. 7 illustrates an optical sensor according to the invention;
  • [0067]
    [0067]FIG. 8 is a block diagram of the main components of a pulse oximeter utilizing the sensor of FIG. 7;
  • [0068]
    [0068]FIG. 9 is a flow chart of a selection process used in the signal processing technique according to the invention; and
  • [0069]
    [0069]FIGS. 10A to 10C are flow charts of three main steps, respectively, of the signal processing method according to the invention.
  • DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
  • [0070]
    Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, FIGS. 1 and 2 illustrate typical hemoglobin spectra and calibrations curve utilized in the pulse oximetry measurements.
  • [0071]
    The present invention provides a sensor for use in a reflection-mode or backscatter type pulse oximeter. The relative disposition of light source and detector in the reflection-mode pulse oximeter are illustrated in FIG. 3.
  • [0072]
    [0072]FIG. 4 shows light propagation in the reflection-mode pulse oximeter where, in addition to the optical absorption and reflection due to blood, the DC signal of the R and IR photoplethysmograms can be adversely affected by strong reflections from the bone.
  • [0073]
    [0073]FIGS. 5A and 5B illustrate a pulse oximeter reflectance sensor operating under, respectively, ideal and practical conditions. Referring now to FIG. 5A, it is shown that, under ideal conditions, reflectance sensor measures light backscattered from a homogenous mixture of blood and bloodless tissue components. Accordingly, the normalized R/IR ratio in dual-wavelength reflection type pulse oximeters, which relies on proportional changes in the AC and DC components in the photoplethysmograms, only reflect changes in arterial oxygen saturation.
  • [0074]
    Referring now to FIG. 5B, in practical situations, the sensor applications affect the distribution of blood in the superficial layers of the skin. Accordingly, the R and IR DC signals measured by photodetectors contain a relatively larger proportion of light absorbed by and reflected from the bloodless tissue compartments. As such, the changes in DC signals depend not only on wavelength but also sensor geometry and thus cannot be eliminated completely by computing the normalized R/IR ratio, as is typically the case in dual-wavelength pulse oximeters. The result is large variations in the slope of the calibration curves, as illustrated in FIG. 6. Referring now to FIG. 6, graphs C1, C2 and C3 show three calibration curves, presenting the variation of the slope for oxygen saturation values between 50% and 100%.
  • [0075]
    Referring to FIG. 7, there is illustrated an optical sensor 10 designed according to the invention aimed at minimizing some of the measurement inaccuracies in a reflectance pulse oximeter. The sensor 10 comprises such main constructional parts as a light source 12 composed of three closely spaced light emitting elements (e.g., LEDs or laser sources) 12 a, 12 b and 12 c generating light of three different wavelengths, respectively, an array of discrete detectors (e.g., photodiodes), a “far” detector 16 and a “near” detector 18, arranged in two concentric ring-like arrangements (constituting closed paths) surrounding the light emitting elements, and a light shield 14. In the present example, six photodiodes form each ring. All these elements are accommodated in a sensor housing 17. The light shield 14 is positioned between the photodiodes and the light emitting elements, and prevents direct optical coupling between them, thereby maximizing the fraction of backscattered light passing through the arterially perfused vascular tissue in the detected light.
  • [0076]
    It should be noted that more than three wavelengths can be utilized in the sensor. The actual numbers of wavelengths used as a light source and the number of photodetectors in each ring are not limited and depend only on the electronic circuitry inside the oximeter. The array of discrete photodiodes can be replaced by one or more continuous photodetector rings.
  • [0077]
    In addition to the R and IR light emitting elements 12 a and 12 b as used in the conventional pulse oximeter sensors, the sensor 10 incorporates the third, reference, light emitting element 12 c, which emits light in the NIR-IR spectrum. Wavelength λ1 and λ2 of the R and IR light emitting elements 12 a and 12 b are centered, respectively, around the peak emission values of 660 nm and 940 nm, and wavelength λ3 of the third light emitting element 12 c has the peak emission value above 700 nm (typically ranging between 800 nm and 900 nm). In the description below, the light emitting elements 12 b and 12 c are referred to as two IR light emitting elements, and wavelengths λ2 and λ3 are referred to as two IR wavelengths.
  • [0078]
    During the operation of the sensor 10, different light emitting elements are selectively operated for illuminating a measurement location (not shown) with different wavelengths. Each of the photodetectors detects reflected light of different wavelengths and generates data indicative of the intensity I of the detected light of different wavelengths.
  • [0079]
    It should be noted that the sensor can be of a compact design utilizing an integrated circuit manufactured by CMOS technology. This technique is disclosed in a copending application assigned to the assignee of the present application. According to this technique, the sensor comprises a package including the light source, a block of two tubular optical waveguides of different diameters concentrically dislocated one inside the other and surrounding the light source, and an integrated circuit plate comprising two ring-like areas of photodiodes positioned concentrically one inside the other. The integrated circuit is also provided with a plurality of printed contact areas and electric conductors intended for mounting the light source thereon, controlling the light source, and transmitting electric signals produced by the photodiodes areas for further processing.
  • [0080]
    [0080]FIG. 8 illustrates a block diagram of a pulse oximeter 20 utilizing the above-described sensor 10. The pulse oximeter typically includes a control unit 21, which is composed of an electronic block 22 including A/D and D/A converters connectable to the sensor 10, a microprocessor 24 for analyzing measured data, and a display 26 for presenting measurement results. The measured data (i.e., electrical output of the sensor 10 indicative of the detected light) is directly processed in the block 22, and the converted signal is further processed by the microprocessor 24. The microprocessor 24 is operated by a suitable software model for analyzing the measured data and utilizing reference data (i.e., calibration curve stored in a memory) to compute the oxygen saturation value, which is then presented on the display 26. The analysis of the measured data utilizes the determination of AC- and DC-components in the detected light for each wavelength, λ1, λ2, and λ3, respectively, i.e., I1 (AC), I1 (DC), I2 (AC), I2 (DC), I3 (AC), and I3 (DC), and the calculation of AC/DC ratio for each wavelength, namely, W1=I1 (AC)/I1 (DC), W2=I2 (AC)/I2 (DC), and W3=I3 (AC)/I3 (DC), as will be described more specifically further below with reference to FIGS. 9 and 10A-10C.
  • [0081]
    The pulse oximeter 20 with the sensor arrangement shown in FIG. 7 provides the following three possible ratio values: W1/W2, W1/W3 and W2/W3. It should be noted that W1/W2 and W1/W3 are the ratios that typically have the highest sensitivity to oxygen saturation. This is due to the fact that λ1 is chosen in the red region of the electromagnetic spectrum, where the changes in the absorption between Hb and HbO2 are the largest, as described above with reference to FIG. 1. Therefore, in principle, the absorption ratios formed by either wavelength pair λ1 and λ2 or wavelength pair λ1 and λ3 can be used to compute the value of SaO2.
  • [0082]
    The inventor conducted extensive human and animal studies, and confirmed that either of the two ratios W1/W2 and W1/W3 can be affected not only by changes in arterial oxygen saturation, but also by sensor placement and by the amount of pressure applied by the sensor on the skin. Any calculation of SaO2 based on either of the two ratios W1/W2 and W1/W3 alone (as normally done in commercially available dual-wavelength pulse oximeters) could result in significant errors. Furthermore, since at least two wavelengths are necessary for the calculation of arterial oxygen saturation, it is not feasible to self-correct the calibration curve for variations due to contact pressure or site-to-site variations utilizing the same two wavelengths used already to compute SaO2.
  • [0083]
    The inventor has found that the third ratio W2/W3 formed by the combination of the two IR wavelengths is mostly dependent on changes in contact pressure or site-to-site variations. Furthermore, this ratio can depend, but to a much lesser degree, on variations in arterial oxygen saturation. The dependency on arterial oxygen saturation, however, is easily minimized or eliminated completely, for example by selection and matching of the peak emission wavelengths and spectral characteristics of the two IR light emitting elements 12 b and 12 c.
  • [0084]
    Generally, the two IR wavelengths λ2 and λ3 are selected to coincide with the region of the optical absorption curve where HbO2 absorbs slightly more light than Hb, but in the spectral region, respectively, where the extinction coefficients of both Hb and HbO2 are nearly equal and remain relatively constant as a function of wavelength. For example, at 940 nm and 880 nm, the optical extinction coefficients of Hb and HbO2 are approximately equal to 0.29 and 0.21, respectively. Therefore, ideally, the ratio of W2/W3 should be close to 1, except for situations when the AC/DC signals measured from λ2 and λ3 are affected unequally causing the ratio W2/W3 to deviate from 1.
  • [0085]
    Fortunately, variations in the ratio W2/W3 mimic changes in the ratios W1/W2 and W1/W3 since these ratios are all affected by similar variations in sensor positioning or other uncontrollable factors that normally can cause large errors in the calibration curve from which oxygen saturation is typically derived. Thus, by tracking in real-time changes in the ratio formed by wavelengths λ2 and λ3, it is possible to automatically correct for errors in the normalized ratios obtained from wavelengths λ1 and λ2, or from λ1 and λ3.
  • [0086]
    The use of an additional third wavelength in the sensor serves another important function (not available in conventional dual-wavelength pulse oximeters), which is associated with the following. Reflectance pulse oximeters have to be capable of detecting and relying on the processing of relatively low quality photoplethysmographic signals. Accordingly, electronic or optical noise can cause large inaccuracies in the final computation of SaO2. Although the amount of electronic or optical noise pickup from the sensor can be minimized to some extent, it is impossible to render the signals measured by the pulse oximeter completely noise free. Therefore, pulse oximeters rely on the assumption that any noise picked up during the measurement would be cancelled by calculating the ratio between the R- and IR-light intensities measured by the photodetector. Practically, however, the amount of noise that is superimposed on the R-and IR-photoplethysmograms cannot be cancelled completely and, thus, can lead to significant errors in the final computation of SaO2 which, in dual-wavelength pulse oximeters, is based only on the ratio between two wavelengths.
  • [0087]
    By utilizing a third wavelength, the invention has the added ability to compute SaO2 based on the ratio formed from either W1/W2 or W1/W3. An algorithm utilized in the pulse oximeter according to the invention has the ability to track and compare in real-time changes between W1/W2 and W1/W3to determine which ratio produces a more stable or less noisy signal and selectively choose the best ratio for calculating SaO2.
  • [0088]
    The method according to the invention utilizes the so-called “selection process” as part of the signal processing technique based on the measured data obtained with the multiple photodetectors. The main steps of the selection process are shown in FIG. 9 in a self-explanatory manner. Here, the symbol i corresponds to a single photodetector element in the array of multiple discrete photodetector elements, the term “1st” signifies the last photodetector element in the array, and the term “DATA” signify three ratios (AC/DC) computed separately for each of the three wavelengths, namely, W1, W2 and W3.
  • [0089]
    The selection process is associated with the following: Practically, each time one of the light emitting elements is in its operative position (i.e., switched on), all of the photodetectors in the sensor receiving backscattered light from the skin. However, the intensity of the backscattered light measured by each photodetector may be different from that measured by the other photodetectors, depending on the anatomical structures underneath the sensor and its orientation relative to these structures.
  • [0090]
    Thus, the selection process is used to discriminate between photodetectors receiving “good” signals (i.e., “good” signal meaning that the calculation of SpO2 from the pulsating portion of the electro-optic signal (AC) and the constant portion (DC) would result in accurate value) and “bad” signals (i.e., having AC and DC values which would result in inaccurate calculations of SpO2). Accordingly, each data point (i.e., ratio W1i, W2i or W3i detected at the corresponding ith detector) is either accepted, if it meets a certain criteria based for example on a certain ratio of AC to DC values (e.g., such that the intensity of AC signal is about 0.05-2.0% of the intensity of DC signal), or rejected. All of the accepted data points (data from accepted detection locations) are then used to calculate the ratios W1/W2, W1/W3 and W2/W3, and to calculate the SpO2 value, in conjunction with the signal processing technique, as will be described further below with reference to FIGS. 10A-10C.
  • [0091]
    Besides the use of the third IR-wavelength to compensate for changes in the internal calibration curve of the pulse oximeter, the pulse oximeter utilizing the sensor according to the invention provides a unique new method to compensate for errors due to sensor positioning and pressure variability. This method is based on multiple photodetector elements, instead of the conventional approach that relies on a single photodetector.
  • [0092]
    While optical sensors with multiple photodetectors for application in reflectance pulse oximetry have been described before, their main limitation relates to the way the information derived from these photodetectors is processed. Although the primary purpose of utilizing multiple photodetectors is to collect a larger portion of the backscattered light from the skin, practically, summing the individual intensities of each photodetector and using the resulting value to compute SaO2 can introduce large errors into the calculations. These errors can be caused, for example, by situations where the sensor is placed over inhomogeneous tissue structures such as when the sensor is mounted on the chest. The case may be such that, when using a continuous photodetector ring to collect the backscattered light, a portion of the photodetector ring lies over a rib, which acts as a strongly reflecting structure that contributes to a strong DC component, and the remaining part of the photodetector is positioned over the intercostals space, where the DC signal is much smaller. In this case, the final calculation of SaO2 would be inaccurate, if the current produced by this photodetector is used indiscriminately to compute the DC value before the final computation of SaO2 is performed. Therefore, in addition to automatically correcting errors in the calibration curve as outlined above using three different LEDs (one R and two different IR wavelengths), the sensor 10 has the optional ability to track automatically and compare changes in the R/IR ratios obtained from each of the discrete photodiodes individually. For example, if some of either the near or the far photodetectors in the two concentrically arranged arrays detect larger than normal DC signals during the operation of one of the photodiodes compared to the other photodiodes in the sensor, it could be indicative of one of the following situations: the sensor is positioned unevenly, the sensor is partially covering a bony structure, or uneven pressure is exerted by the sensor on the skin causing partial skin “blanching” and therefore the blood-to-bloodless tissue ratio might be too high to allow accurate determination of SaO2. If such a situation is detected, the oximeter has the ability to selectively disregard the readings obtained from the corresponding photodetectors. Otherwise, if the DC and AC signals measured from each photodetector in the array are similar in magnitude, which is an indication that the sensor is positioned over a homogeneous area on the skin, the final computation of SaO2 can be based on equal contributions from every photodetector in the array.
  • [0093]
    Turning now to FIGS. 10A, 10B and 10C, there are illustrated three main steps of the signal processing technique utilized in the present invention. Here, TH1, and TH2 are two different threshold values (determined experimentally) related respectively to W2/W3 and (W1/W2−W1/W3).
  • [0094]
    During step 1 (FIG. 10A), measured data generated by the “near” and “far” photodetectors indicative of the detected (backscattered) light of wavelength λ2 and λ3 is analyzed to calculate the two ratios W2/W3 (far and near). If one of the calculated ratios (far or near) is not in the range of 1±TH1 (TH1 is for example 0.1), then this data point is rejected from the SpO2 calculation, but if both of them are not in the mentioned range, a corresponding alarm is generated indicative of that the sensor position should be adjusted. Only if there are calculated ratios which are in the range of 1±TH1, they are accepted and the process (data analysis) proceeds by performing step 2.
  • [0095]
    Step 2 (FIG. 10B) consists of determining whether the quality of each photoplethysmogram is acceptable or not. The quality determination is based on the relative magnitude of each AC component compared to its corresponding DC component. If the quality is not acceptable (e.g., the signal shape detected by any detector varies within a time frame of the measurement session, which may for example be 3.5 sec), the data point is rejected and a corresponding alarm signal is generated. If the AC/DC ratio of W1, W2 and W3 are within an acceptable range, the respective data point is accepted, and the process proceeds through performing step 3.
  • [0096]
    In step 3 (FIG. 10C), the measured data is analyzed to calculate ratios W1/W2 and W1/W3 from data generated by far and near photodetectors, and to calculate the differences (W1/W2−W1W3).
  • [0097]
    In a perfect situation, W1/W2 (far) is very close to W1/W3 (far), and W1/W2 (near) is very close to W1/W3 (near). In a practical situation, this condition is not precisely satisfied, but all the ratios are close to each other if the measurement situation is “good”.
  • [0098]
    Then, the calculated differences are analyzed to determine the values (corresponding to far and near photodetectors) that are accepted and to use them in the SpO2 calculation. For each detector that satisfied the condition ABS(W1/W2−W1/W3)<TH2), where ABS signifies the absolute value, its respective data point is accepted and used to calculate the oxygen saturation value that will be displayed. If the condition is not satisfied, the data point is rejected. If all data points are rejected, another measurement session is carried out.
  • [0099]
    It should be noted that, although the steps 1-3 above are exemplified with respect to signal detection by both near and far photodetectors, each of these steps can be implemented by utilizing only one array of detection locations along the closed path. The provision of two such arrays, however, provides higher accuracy of measurements.
Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US5178142 *Jul 3, 1991Jan 12, 1993Vivascan CorporationElectromagnetic method and apparatus to measure constituents of human or animal tissue
US5433197 *Sep 4, 1992Jul 18, 1995Stark; Edward W.Non-invasive glucose measurement method and apparatus
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US6711425 *May 28, 2002Mar 23, 2004Ob Scientific, Inc.Pulse oximeter with calibration stabilization
US7209775 *Apr 15, 2004Apr 24, 2007Samsung Electronics Co., Ltd.Ear type apparatus for measuring a bio signal and measuring method therefor
US7647084Jul 28, 2006Jan 12, 2010Nellcor Puritan Bennett LlcMedical sensor and technique for using the same
US7650177Aug 1, 2006Jan 19, 2010Nellcor Puritan Bennett LlcMedical sensor for reducing motion artifacts and technique for using the same
US7657294Aug 8, 2005Feb 2, 2010Nellcor Puritan Bennett LlcCompliant diaphragm medical sensor and technique for using the same
US7657295Feb 2, 2010Nellcor Puritan Bennett LlcMedical sensor and technique for using the same
US7657296Jul 28, 2006Feb 2, 2010Nellcor Puritan Bennett LlcUnitary medical sensor assembly and technique for using the same
US7658652Feb 9, 2010Nellcor Puritan Bennett LlcDevice and method for reducing crosstalk
US7676253Mar 9, 2010Nellcor Puritan Bennett LlcMedical sensor and technique for using the same
US7680522Sep 29, 2006Mar 16, 2010Nellcor Puritan Bennett LlcMethod and apparatus for detecting misapplied sensors
US7684842Mar 23, 2010Nellcor Puritan Bennett LlcSystem and method for preventing sensor misuse
US7684843Mar 23, 2010Nellcor Puritan Bennett LlcMedical sensor and technique for using the same
US7693559Apr 6, 2010Nellcor Puritan Bennett LlcMedical sensor having a deformable region and technique for using the same
US7698002Apr 13, 2010Nellcor Puritan Bennett LlcSystems and methods for user interface and identification in a medical device
US7698909Feb 13, 2004Apr 20, 2010Nellcor Puritan Bennett LlcHeadband with tension indicator
US7706896Sep 29, 2006Apr 27, 2010Nellcor Puritan Bennett LlcUser interface and identification in a medical device system and method
US7720516Nov 16, 2004May 18, 2010Nellcor Puritan Bennett LlcMotion compatible sensor for non-invasive optical blood analysis
US7725146Sep 29, 2005May 25, 2010Nellcor Puritan Bennett LlcSystem and method for pre-processing waveforms
US7725147Sep 29, 2005May 25, 2010Nellcor Puritan Bennett LlcSystem and method for removing artifacts from waveforms
US7729736Aug 30, 2006Jun 1, 2010Nellcor Puritan Bennett LlcMedical sensor and technique for using the same
US7738937Jul 28, 2006Jun 15, 2010Nellcor Puritan Bennett LlcMedical sensor and technique for using the same
US7794266Sep 14, 2010Nellcor Puritan Bennett LlcDevice and method for reducing crosstalk
US7796403Sep 14, 2010Nellcor Puritan Bennett LlcMeans for mechanical registration and mechanical-electrical coupling of a faraday shield to a photodetector and an electrical circuit
US7809420Jul 26, 2006Oct 5, 2010Nellcor Puritan Bennett LlcHat-based oximeter sensor
US7810359Oct 12, 2010Nellcor Puritan Bennett LlcHeadband with tension indicator
US7813779Jul 26, 2006Oct 12, 2010Nellcor Puritan Bennett LlcHat-based oximeter sensor
US7822453Oct 26, 2010Nellcor Puritan Bennett LlcForehead sensor placement
US7848891Sep 29, 2006Dec 7, 2010Nellcor Puritan Bennett LlcModulation ratio determination with accommodation of uncertainty
US7869849Jan 11, 2011Nellcor Puritan Bennett LlcOpaque, electrically nonconductive region on a medical sensor
US7869850Sep 29, 2005Jan 11, 2011Nellcor Puritan Bennett LlcMedical sensor for reducing motion artifacts and technique for using the same
US7877126Jul 26, 2006Jan 25, 2011Nellcor Puritan Bennett LlcHat-based oximeter sensor
US7877127Jul 26, 2006Jan 25, 2011Nellcor Puritan Bennett LlcHat-based oximeter sensor
US7880884Feb 1, 2011Nellcor Puritan Bennett LlcSystem and method for coating and shielding electronic sensor components
US7881762Sep 30, 2005Feb 1, 2011Nellcor Puritan Bennett LlcClip-style medical sensor and technique for using the same
US7887345Jun 30, 2008Feb 15, 2011Nellcor Puritan Bennett LlcSingle use connector for pulse oximetry sensors
US7890153Feb 15, 2011Nellcor Puritan Bennett LlcSystem and method for mitigating interference in pulse oximetry
US7890154Dec 3, 2008Feb 15, 2011Nellcor Puritan Bennett LlcSelection of ensemble averaging weights for a pulse oximeter based on signal quality metrics
US7894869Mar 9, 2007Feb 22, 2011Nellcor Puritan Bennett LlcMultiple configuration medical sensor and technique for using the same
US7899509Jul 28, 2006Mar 1, 2011Nellcor Puritan Bennett LlcForehead sensor placement
US7899510Mar 1, 2011Nellcor Puritan Bennett LlcMedical sensor and technique for using the same
US7904130Mar 8, 2011Nellcor Puritan Bennett LlcMedical sensor and technique for using the same
US7922665Sep 28, 2006Apr 12, 2011Nellcor Puritan Bennett LlcSystem and method for pulse rate calculation using a scheme for alternate weighting
US7925511Apr 12, 2011Nellcor Puritan Bennett LlcSystem and method for secure voice identification in a medical device
US7979102Feb 21, 2006Jul 12, 2011Nellcor Puritan Bennett LlcHat-based oximeter sensor
US8007441May 7, 2009Aug 30, 2011Nellcor Puritan Bennett LlcPulse oximeter with alternate heart-rate determination
US8060171Aug 1, 2006Nov 15, 2011Nellcor Puritan Bennett LlcMedical sensor for reducing motion artifacts and technique for using the same
US8062221Sep 30, 2005Nov 22, 2011Nellcor Puritan Bennett LlcSensor for tissue gas detection and technique for using the same
US8064975Nov 22, 2011Nellcor Puritan Bennett LlcSystem and method for probability based determination of estimated oxygen saturation
US8068890Nov 29, 2011Nellcor Puritan Bennett LlcPulse oximetry sensor switchover
US8068891Sep 29, 2006Nov 29, 2011Nellcor Puritan Bennett LlcSymmetric LED array for pulse oximetry
US8070508Dec 6, 2011Nellcor Puritan Bennett LlcMethod and apparatus for aligning and securing a cable strain relief
US8071935Jun 30, 2008Dec 6, 2011Nellcor Puritan Bennett LlcOptical detector with an overmolded faraday shield
US8073518May 2, 2006Dec 6, 2011Nellcor Puritan Bennett LlcClip-style medical sensor and technique for using the same
US8092379Sep 29, 2005Jan 10, 2012Nellcor Puritan Bennett LlcMethod and system for determining when to reposition a physiological sensor
US8092993Jan 10, 2012Nellcor Puritan Bennett LlcHydrogel thin film for use as a biosensor
US8095192Dec 2, 2005Jan 10, 2012Nellcor Puritan Bennett LlcSignal quality metrics design for qualifying data for a physiological monitor
US8112375Mar 27, 2009Feb 7, 2012Nellcor Puritan Bennett LlcWavelength selection and outlier detection in reduced rank linear models
US8126525Dec 1, 2006Feb 28, 2012Ge Healthcare Finland OyProbe and a method for use with a probe
US8133176Sep 30, 2005Mar 13, 2012Tyco Healthcare Group LpMethod and circuit for indicating quality and accuracy of physiological measurements
US8140272Mar 27, 2009Mar 20, 2012Nellcor Puritan Bennett LlcSystem and method for unmixing spectroscopic observations with nonnegative matrix factorization
US8145288Aug 22, 2006Mar 27, 2012Nellcor Puritan Bennett LlcMedical sensor for reducing signal artifacts and technique for using the same
US8148164 *Dec 30, 2009Apr 3, 2012Roche Diagnostics Operations, Inc.System and method for determining the concentration of an analyte in a sample fluid
US8160668Sep 29, 2006Apr 17, 2012Nellcor Puritan Bennett LlcPathological condition detector using kernel methods and oximeters
US8160683Dec 30, 2010Apr 17, 2012Nellcor Puritan Bennett LlcSystem and method for integrating voice with a medical device
US8160726Feb 16, 2010Apr 17, 2012Nellcor Puritan Bennett LlcUser interface and identification in a medical device system and method
US8175667May 8, 2012Nellcor Puritan Bennett LlcSymmetric LED array for pulse oximetry
US8175670Sep 15, 2006May 8, 2012Nellcor Puritan Bennett LlcPulse oximetry signal correction using near infrared absorption by water
US8175671Sep 22, 2006May 8, 2012Nellcor Puritan Bennett LlcMedical sensor for reducing signal artifacts and technique for using the same
US8190224May 29, 2012Nellcor Puritan Bennett LlcMedical sensor for reducing signal artifacts and technique for using the same
US8190225May 29, 2012Nellcor Puritan Bennett LlcMedical sensor for reducing signal artifacts and technique for using the same
US8195262Jun 5, 2012Nellcor Puritan Bennett LlcSwitch-mode oximeter LED drive with a single inductor
US8195263Sep 18, 2007Jun 5, 2012Nellcor Puritan Bennett LlcPulse oximetry motion artifact rejection using near infrared absorption by water
US8195264Jun 5, 2012Nellcor Puritan Bennett LlcMedical sensor for reducing signal artifacts and technique for using the same
US8199007Jun 12, 2012Nellcor Puritan Bennett LlcFlex circuit snap track for a biometric sensor
US8204567Dec 13, 2007Jun 19, 2012Nellcor Puritan Bennett LlcSignal demodulation
US8219170Jul 10, 2012Nellcor Puritan Bennett LlcSystem and method for practicing spectrophotometry using light emitting nanostructure devices
US8221319Jul 17, 2012Nellcor Puritan Bennett LlcMedical device for assessing intravascular blood volume and technique for using the same
US8233954Jul 31, 2012Nellcor Puritan Bennett LlcMucosal sensor for the assessment of tissue and blood constituents and technique for using the same
US8238994Jun 12, 2009Aug 7, 2012Nellcor Puritan Bennett LlcAdjusting parameters used in pulse oximetry analysis
US8257274Sep 4, 2012Nellcor Puritan Bennett LlcMedical sensor and technique for using the same
US8260391Sep 4, 2012Nellcor Puritan Bennett LlcMedical sensor for reducing motion artifacts and technique for using the same
US8265724Mar 9, 2007Sep 11, 2012Nellcor Puritan Bennett LlcCancellation of light shunting
US8275553Sep 25, 2012Nellcor Puritan Bennett LlcSystem and method for evaluating physiological parameter data
US8280469Mar 9, 2007Oct 2, 2012Nellcor Puritan Bennett LlcMethod for detection of aberrant tissue spectra
US8290558 *Nov 23, 2009Oct 16, 2012Vioptix, Inc.Tissue oximeter intraoperative sensor
US8292809Oct 23, 2012Nellcor Puritan Bennett LlcDetecting chemical components from spectroscopic observations
US8298828Oct 30, 2012Roche Diagnostics Operations, Inc.System and method for determining the concentration of an analyte in a sample fluid
US8311601Nov 13, 2012Nellcor Puritan Bennett LlcReflectance and/or transmissive pulse oximeter
US8311602Nov 13, 2012Nellcor Puritan Bennett LlcCompliant diaphragm medical sensor and technique for using the same
US8315684Nov 20, 2012Covidien LpOximeter ambient light cancellation
US8315685Jun 25, 2009Nov 20, 2012Nellcor Puritan Bennett LlcFlexible medical sensor enclosure
US8346328Jan 1, 2013Covidien LpMedical sensor and technique for using the same
US8352004Jan 8, 2013Covidien LpMedical sensor and technique for using the same
US8352009Jan 5, 2009Jan 8, 2013Covidien LpMedical sensor and technique for using the same
US8352010May 26, 2009Jan 8, 2013Covidien LpFolding medical sensor and technique for using the same
US8364220Sep 25, 2008Jan 29, 2013Covidien LpMedical sensor and technique for using the same
US8364221Jan 29, 2013Covidien LpPatient monitoring alarm escalation system and method
US8364224Jan 29, 2013Covidien LpSystem and method for facilitating sensor and monitor communication
US8366613Dec 24, 2008Feb 5, 2013Covidien LpLED drive circuit for pulse oximetry and method for using same
US8376955Sep 29, 2009Feb 19, 2013Covidien LpSpectroscopic method and system for assessing tissue temperature
US8386000Feb 26, 2013Covidien LpSystem and method for photon density wave pulse oximetry and pulse hemometry
US8386002Feb 26, 2013Covidien LpOptically aligned pulse oximetry sensor and technique for using the same
US8391941Jul 17, 2009Mar 5, 2013Covidien LpSystem and method for memory switching for multiple configuration medical sensor
US8391943Mar 31, 2010Mar 5, 2013Covidien LpMulti-wavelength photon density wave system using an optical switch
US8396527Sep 22, 2006Mar 12, 2013Covidien LpMedical sensor for reducing signal artifacts and technique for using the same
US8401606Mar 19, 2013Covidien LpNuisance alarm reductions in a physiological monitor
US8401607Mar 19, 2013Covidien LpNuisance alarm reductions in a physiological monitor
US8401608Mar 19, 2013Covidien LpMethod of analyzing photon density waves in a medical monitor
US8412297Jul 28, 2006Apr 2, 2013Covidien LpForehead sensor placement
US8417309Apr 9, 2013Covidien LpMedical sensor
US8417310Apr 9, 2013Covidien LpDigital switching in multi-site sensor
US8420404 *Apr 16, 2013Roche Diagnostics Operations, Inc.System and method for determining the concentration of an analyte in a sample fluid
US8423109Jun 20, 2008Apr 16, 2013Covidien LpMethod for enhancing pulse oximery calculations in the presence of correlated artifacts
US8423112Apr 16, 2013Covidien LpMedical sensor and technique for using the same
US8428675Aug 19, 2009Apr 23, 2013Covidien LpNanofiber adhesives used in medical devices
US8433382Apr 30, 2013Covidien LpTransmission mode photon density wave system and method
US8433383Apr 30, 2013Covidien LpStacked adhesive optical sensor
US8437822Mar 27, 2009May 7, 2013Covidien LpSystem and method for estimating blood analyte concentration
US8437826Nov 7, 2011May 7, 2013Covidien LpClip-style medical sensor and technique for using the same
US8442608May 14, 2013Covidien LpSystem and method for estimating physiological parameters by deconvolving artifacts
US8452364Dec 24, 2008May 28, 2013Covidien LLPSystem and method for attaching a sensor to a patient's skin
US8452366Mar 16, 2009May 28, 2013Covidien LpMedical monitoring device with flexible circuitry
US8452367Jul 26, 2010May 28, 2013Covidien LpForehead sensor placement
US8483790Mar 7, 2007Jul 9, 2013Covidien LpNon-adhesive oximeter sensor for sensitive skin
US8494604Sep 21, 2009Jul 23, 2013Covidien LpWavelength-division multiplexing in a multi-wavelength photon density wave system
US8494606Aug 19, 2009Jul 23, 2013Covidien LpPhotoplethysmography with controlled application of sensor pressure
US8494786Jul 30, 2009Jul 23, 2013Covidien LpExponential sampling of red and infrared signals
US8498683Apr 30, 2010Jul 30, 2013Covidien LLPMethod for respiration rate and blood pressure alarm management
US8505821Jun 30, 2009Aug 13, 2013Covidien LpSystem and method for providing sensor quality assurance
US8509869May 15, 2009Aug 13, 2013Covidien LpMethod and apparatus for detecting and analyzing variations in a physiologic parameter
US8515511Sep 29, 2009Aug 20, 2013Covidien LpSensor with an optical coupling material to improve plethysmographic measurements and method of using the same
US8515515Mar 11, 2010Aug 20, 2013Covidien LpMedical sensor with compressible light barrier and technique for using the same
US8528185Aug 21, 2009Sep 10, 2013Covidien LpBi-stable medical sensor and technique for using the same
US8538500Oct 20, 2011Sep 17, 2013Covidien LpSystem and method for probability based determination of estimated oxygen saturation
US8560036Dec 28, 2010Oct 15, 2013Covidien LpSelection of ensemble averaging weights for a pulse oximeter based on signal quality metrics
US8571621Jun 24, 2010Oct 29, 2013Covidien LpMinimax filtering for pulse oximetry
US8577434Dec 24, 2008Nov 5, 2013Covidien LpCoaxial LED light sources
US8577436Mar 5, 2012Nov 5, 2013Covidien LpMedical sensor for reducing signal artifacts and technique for using the same
US8586373Oct 24, 2012Nov 19, 2013Roche Diagnostics Operations, Inc.System and method for determining the concentration of an analyte in a sample fluid
US8600469Feb 7, 2011Dec 3, 2013Covidien LpMedical sensor and technique for using the same
US8610769Feb 28, 2011Dec 17, 2013Covidien LpMedical monitor data collection system and method
US8611977Mar 8, 2004Dec 17, 2013Covidien LpMethod and apparatus for optical detection of mixed venous and arterial blood pulsation in tissue
US8622916Oct 30, 2009Jan 7, 2014Covidien LpSystem and method for facilitating observation of monitored physiologic data
US8634891May 20, 2009Jan 21, 2014Covidien LpMethod and system for self regulation of sensor component contact pressure
US8649838Sep 22, 2010Feb 11, 2014Covidien LpWavelength switching for pulse oximetry
US8660626Feb 4, 2011Feb 25, 2014Covidien LpSystem and method for mitigating interference in pulse oximetry
US8666467Jun 13, 2012Mar 4, 2014Lawrence A. LynnSystem and method for SPO2 instability detection and quantification
US8696593Sep 27, 2006Apr 15, 2014Covidien LpMethod and system for monitoring intracranial pressure
US8702606May 16, 2008Apr 22, 2014Covidien LpPatient monitoring help video system and method
US8704666Sep 21, 2009Apr 22, 2014Covidien LpMedical device interface customization systems and methods
US8728001Jan 7, 2010May 20, 2014Lawrence A. LynnNasal capnographic pressure monitoring system
US8728059Sep 29, 2006May 20, 2014Covidien LpSystem and method for assuring validity of monitoring parameter in combination with a therapeutic device
US8744543May 21, 2010Jun 3, 2014Covidien LpSystem and method for removing artifacts from waveforms
US8750953Feb 18, 2009Jun 10, 2014Covidien LpMethods and systems for alerting practitioners to physiological conditions
US8761851 *Dec 6, 2006Jun 24, 2014Cas Medical Systems, Inc.Indicators for a spectrophotometric system
US8781548Mar 11, 2010Jul 15, 2014Covidien LpMedical sensor with flexible components and technique for using the same
US8781753Sep 6, 2012Jul 15, 2014Covidien LpSystem and method for evaluating physiological parameter data
US8788001Sep 21, 2009Jul 22, 2014Covidien LpTime-division multiplexing in a multi-wavelength photon density wave system
US8798704Sep 13, 2010Aug 5, 2014Covidien LpPhotoacoustic spectroscopy method and system to discern sepsis from shock
US8801622Mar 7, 2011Aug 12, 2014Covidien LpSystem and method for pulse rate calculation using a scheme for alternate weighting
US8818475Mar 28, 2013Aug 26, 2014Covidien LpMethod for enhancing pulse oximetry calculations in the presence of correlated artifacts
US8838196Mar 14, 2013Sep 16, 2014Covidien LpNuisance alarm reductions in a physiological monitor
US8855749Aug 16, 2010Oct 7, 2014Covidien LpDetermination of a physiological parameter
US8862194Jun 30, 2008Oct 14, 2014Covidien LpMethod for improved oxygen saturation estimation in the presence of noise
US8862196May 6, 2011Oct 14, 2014Lawrence A. LynnSystem and method for automatic detection of a plurality of SP02 time series pattern types
US8874181Oct 29, 2012Oct 28, 2014Covidien LpOximeter ambient light cancellation
US8897850Dec 29, 2008Nov 25, 2014Covidien LpSensor with integrated living hinge and spring
US8914088Sep 30, 2008Dec 16, 2014Covidien LpMedical sensor and technique for using the same
US8923945Sep 13, 2010Dec 30, 2014Covidien LpDetermination of a physiological parameter
US8930145Jul 28, 2010Jan 6, 2015Covidien LpLight focusing continuous wave photoacoustic spectroscopy and its applications to patient monitoring
US8932227Feb 10, 2006Jan 13, 2015Lawrence A. LynnSystem and method for CO2 and oximetry integration
US8965473Oct 6, 2011Feb 24, 2015Covidien LpMedical sensor for reducing motion artifacts and technique for using the same
US8968193Sep 30, 2008Mar 3, 2015Covidien LpSystem and method for enabling a research mode on physiological monitors
US8983800Oct 11, 2005Mar 17, 2015Covidien LpSelection of preset filter parameters based on signal quality
US9010634Jun 30, 2009Apr 21, 2015Covidien LpSystem and method for linking patient data to a patient and providing sensor quality assurance
US9031793Sep 5, 2012May 12, 2015Lawrence A. LynnCentralized hospital monitoring system for automatically detecting upper airway instability and for preventing and aborting adverse drug reactions
US9037204Sep 7, 2011May 19, 2015Covidien LpFiltered detector array for optical patient sensors
US9042952Feb 10, 2006May 26, 2015Lawrence A. LynnSystem and method for automatic detection of a plurality of SPO2 time series pattern types
US9053222May 7, 2009Jun 9, 2015Lawrence A. LynnPatient safety processor
US9149192 *May 26, 2006Oct 6, 2015Sotera Wireless, Inc.System for measuring vital signs using bilateral pulse transit time
US9314164Mar 15, 2013Apr 19, 2016Northwestern UniversityMethod of using the detection of early increase in microvascular blood content to distinguish between adenomatous and hyperplastic polyps
US9351671Sep 22, 2014May 31, 2016Timothy RuchtiMultiplexed pathlength resolved noninvasive analyzer apparatus and method of use thereof
US9351672Sep 22, 2014May 31, 2016Timothy RuchtiMultiplexed pathlength resolved noninvasive analyzer apparatus with stacked filters and method of use thereof
US9351674Aug 4, 2014May 31, 2016Covidien LpMethod for enhancing pulse oximetry calculations in the presence of correlated artifacts
US9375170Nov 11, 2015Jun 28, 2016Timothy RuchtiMultiplexed pathlength resolved noninvasive analyzer apparatus with stacked filters and method of use thereof
US9380969Jul 8, 2013Jul 5, 2016Covidien LpSystems and methods for varying a sampling rate of a signal
US9380982Jul 28, 2010Jul 5, 2016Covidien LpAdaptive alarm system and method
US20040225207 *Apr 15, 2004Nov 11, 2004Sang-Kon BaeEar type apparatus for measuring a bio signal and measuring method therefor
US20050197579 *Mar 8, 2004Sep 8, 2005Nellcor Puritan Bennett IncorporatedMethod and apparatus for optical detection of mixed venous and arterial blood pulsation in tissue
US20060020212 *Jul 26, 2004Jan 26, 2006Tianning XuPortable vein locating device
US20060135860 *Dec 2, 2005Jun 22, 2006Baker Clark R JrSignal quality metrics design for qualifying data for a physiological monitor
US20060155178 *Oct 27, 2005Jul 13, 2006Vadim BackmanMulti-dimensional elastic light scattering
US20070032714 *Oct 16, 2006Feb 8, 2007Nellcor Puritan Bennett Inc.Nuisance alarm reductions in a physiological monitor
US20070073124 *Sep 29, 2005Mar 29, 2007Li LiSystem and method for removing artifacts from waveforms
US20070106137 *Sep 15, 2006May 10, 2007Baker Clark R JrPulse oximetry signal correction using near infrared absorption by water
US20070129615 *Nov 27, 2006Jun 7, 2007Northwestern UniversityApparatus for recognizing abnormal tissue using the detection of early increase in microvascular blood content
US20070129616 *Dec 1, 2006Jun 7, 2007Borje RantalaProbe and a method for use with a probe
US20070179368 *Nov 27, 2006Aug 2, 2007Northwestern UniversityMethod of recognizing abnormal tissue using the detection of early increase in microvascular blood content
US20070208259 *Mar 6, 2006Sep 6, 2007Mannheimer Paul DPatient monitoring alarm escalation system and method
US20070276632 *May 26, 2006Nov 29, 2007Triage Wireless, Inc.System for measuring vital signs using bilateral pulse transit time
US20080009690 *Sep 18, 2007Jan 10, 2008Nellcor Puritan Bennett LlcPulse oximetry motion artifact rejection using near infrared absorption by water
US20080051670 *Oct 31, 2007Feb 28, 2008Triage Wireless, Inc.Patch sensor system for measuring vital signs
US20080076977 *Sep 26, 2006Mar 27, 2008Nellcor Puritan Bennett Inc.Patient monitoring device snapshot feature system and method
US20080076986 *Sep 20, 2006Mar 27, 2008Nellcor Puritan Bennett Inc.System and method for probability based determination of estimated oxygen saturation
US20080081956 *Sep 29, 2006Apr 3, 2008Jayesh ShahSystem and method for integrating voice with a medical device
US20080081970 *Sep 29, 2006Apr 3, 2008Nellcor Puritan Bennett IncorporatedPulse oximetry sensor switchover
US20080081974 *Sep 29, 2006Apr 3, 2008Nellcor Puritan Bennett IncorporatedPathological condition detector using kernel methods and oximeters
US20080082009 *Sep 28, 2006Apr 3, 2008Nellcor Puritan Bennett Inc.System and method for pulse rate calculation using a scheme for alternate weighting
US20080082338 *Sep 29, 2006Apr 3, 2008O'neil Michael PSystems and methods for secure voice identification and medical device interface
US20080082339 *Sep 29, 2006Apr 3, 2008Nellcor Puritan Bennett IncorporatedSystem and method for secure voice identification in a medical device
US20080097175 *Sep 29, 2006Apr 24, 2008Boyce Robin SSystem and method for display control of patient monitor
US20080114211 *Sep 29, 2006May 15, 2008Edward KarstSystem and method for assuring validity of monitoring parameter in combination with a therapeutic device
US20080114226 *Sep 29, 2006May 15, 2008Doug MusicSystems and methods for user interface and identification in a medical device
US20080189783 *Sep 29, 2006Aug 7, 2008Doug MusicUser interface and identification in a medical device system and method
US20080200775 *Feb 20, 2007Aug 21, 2008Lynn Lawrence AManeuver-based plethysmographic pulse variation detection system and method
US20080200819 *Feb 20, 2007Aug 21, 2008Lynn Lawrence AOrthostasis detection system and method
US20080214906 *May 16, 2008Sep 4, 2008Nellcor Puritan Bennett LlcPatient Monitoring Help Video System and Method
US20080221426 *Mar 9, 2007Sep 11, 2008Nellcor Puritan Bennett LlcMethods and apparatus for detecting misapplied optical sensors
US20080255436 *Jun 20, 2008Oct 16, 2008Nellcor Puritain Bennett IncorporatedMethod for Enhancing Pulse Oximery Calculations in the Presence of Correlated Artifacts
US20080300474 *Dec 6, 2006Dec 4, 2008Cas Medical Systems, Inc.Indicators For A Spectrophotometric System
US20090005662 *Jul 14, 2008Jan 1, 2009Nellcor Puritan Bennett IncOximeter Ambient Light Cancellation
US20090082651 *Dec 3, 2008Mar 26, 2009Nellcor Puritan Bennett LlcSelection of ensemble averaging weights for a pulse oximeter based on signal quality metrics
US20090105564 *Jun 8, 2006Apr 23, 2009Omron Healthcare Co., Ltd.Living body component measuring apparatus capable of precisely and non-invasively measuring living body component
US20090154573 *Dec 13, 2007Jun 18, 2009Nellcor Puritan Bennett LlcSignal Demodulation
US20090171167 *Dec 23, 2008Jul 2, 2009Nellcor Puritan Bennett LlcSystem And Method For Monitor Alarm Management
US20090171171 *Dec 22, 2008Jul 2, 2009Nellcor Puritan Bennett LlcOximetry sensor overmolding location features
US20090171172 *Dec 19, 2008Jul 2, 2009Nellcor Puritan Bennett LlcMethod and system for pulse gating
US20090171173 *Dec 22, 2008Jul 2, 2009Nellcor Puritan Bennett LlcSystem and method for reducing motion artifacts in a sensor
US20090171174 *Dec 22, 2008Jul 2, 2009Nellcor Puritan Bennett LlcSystem and method for maintaining battery life
US20090171226 *Dec 22, 2008Jul 2, 2009Nellcor Puritan Bennett LlcSystem and method for evaluating variation in the timing of physiological events
US20090203977 *Jan 8, 2009Aug 13, 2009Vadim BackmanMethod of screening for cancer using parameters obtained by the detection of early increase in microvascular blood content
US20090209839 *Feb 18, 2009Aug 20, 2009Nellcor Puritan Bennett LlcMethods And Systems For Alerting Practitioners To Physiological Conditions
US20090221889 *May 7, 2009Sep 3, 2009Nellcor Puritan Bennett LlcPulse Oximeter With Alternate Heart-Rate Determination
US20090247850 *Mar 27, 2009Oct 1, 2009Nellcor Puritan Bennett LlcManually Powered Oximeter
US20090247851 *Mar 24, 2009Oct 1, 2009Nellcor Puritan Bennett LlcGraphical User Interface For Monitor Alarm Management
US20090247852 *Mar 31, 2009Oct 1, 2009Nellcor Puritan Bennett LlcSystem and method for facilitating sensor and monitor communication
US20090248320 *Mar 27, 2009Oct 1, 2009Nellcor Puritan Benett LlcSystem And Method For Unmixing Spectroscopic Observations With Nonnegative Matrix Factorization
US20090253971 *Jun 12, 2009Oct 8, 2009Nellcor Puritan Bennett LlcAdjusting parameters used in pulse oximetry analysis
US20090326335 *Dec 31, 2009Baker Clark RPulse Oximeter With Wait-Time Indication
US20090327515 *Dec 31, 2009Thomas PriceMedical Monitor With Network Connectivity
US20100081890 *Sep 30, 2008Apr 1, 2010Nellcor Puritan Bennett LlcSystem And Method For Enabling A Research Mode On Physiological Monitors
US20100081897 *Jul 30, 2009Apr 1, 2010Nellcor Puritan Bennett LlcTransmission Mode Photon Density Wave System And Method
US20100081899 *Sep 30, 2008Apr 1, 2010Nellcor Puritan Bennett LlcSystem and Method for Photon Density Wave Pulse Oximetry and Pulse Hemometry
US20100113908 *Oct 30, 2009May 6, 2010Nellcor Puritan Bennett LlcSystem And Method For Facilitating Observation Of Monitored Physiologic Data
US20100113909 *Oct 30, 2009May 6, 2010Nellcor Puritan Bennett LlcSystem And Method For Facilitating Observation Of Monitored Physiologic Data
US20100141391 *Feb 16, 2010Jun 10, 2010Nellcor Puritan Bennett LlcUser interface and identification in a medical device system and method
US20100145170 *May 27, 2009Jun 10, 2010Starr Life Sciences Corp.Small Animal Pulse Oximeter User Interface
US20100240972 *Sep 23, 2010Nellcor Puritan Bennett LlcSlider Spot Check Pulse Oximeter
US20110029865 *Feb 3, 2011Nellcor Puritan Bennett LlcControl Interface For A Medical Monitor
US20110046464 *Aug 19, 2009Feb 24, 2011Nellcor Puritan Bennett LlcPhotoplethysmography with controlled application of sensor pressure
US20110071368 *Mar 24, 2011Nellcor Puritan Bennett LlcMedical Device Interface Customization Systems And Methods
US20110071371 *Sep 21, 2009Mar 24, 2011Nellcor Puritan Bennett LlcWavelength-Division Multiplexing In A Multi-Wavelength Photon Density Wave System
US20110071373 *Mar 24, 2011Nellcor Puritan Bennett LlcTime-Division Multiplexing In A Multi-Wavelength Photon Density Wave System
US20110071374 *Jun 24, 2010Mar 24, 2011Nellcor Puritan Bennett LlcMinimax Filtering For Pulse Oximetry
US20110071376 *Mar 24, 2011Nellcor Puritan Bennett LlcDetermination Of A Physiological Parameter
US20110071598 *Sep 13, 2010Mar 24, 2011Nellcor Puritan Bennett LlcPhotoacoustic Spectroscopy Method And System To Discern Sepsis From Shock
US20110074342 *Mar 31, 2011Nellcor Puritan Bennett LlcWireless electricity for electronic devices
US20110077470 *Mar 31, 2011Nellcor Puritan Bennett LlcPatient Monitor Symmetry Control
US20110077485 *Sep 30, 2009Mar 31, 2011Nellcor Puritan Bennett LlcMethod Of Analyzing Photon Density Waves In A Medical Monitor
US20110077547 *Sep 29, 2009Mar 31, 2011Nellcor Puritan Bennett LlcSpectroscopic Method And System For Assessing Tissue Temperature
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US20110098544 *Dec 30, 2010Apr 28, 2011Nellcor Puritan Bennett LlcSystem and method for integrating voice with a medical device
US20150011850 *Sep 22, 2014Jan 8, 2015Timothy RuchtiMultiplexed pathlength resolved noninvasive analyzer apparatus with dynamic optical paths and method of use thereof
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USD736250Oct 8, 2010Aug 11, 2015Covidien LpPortion of a display panel with an indicator icon
EP1792564A1 *Dec 2, 2005Jun 6, 2007General Electric CompanyA probe and a method for use with a probe
WO2016087609A1 *Dec 3, 2015Jun 9, 2016Osram Opto Semiconductors GmbhPulse oximetry device and method for operating a pulse oximetry device
Classifications
U.S. Classification600/323, 600/322
International ClassificationA61B5/1455, G01N21/35, A61B5/00, A61B5/1464, G01N21/27, A61B5/145
Cooperative ClassificationA61B5/14552, A61B5/1455
European ClassificationA61B5/1455, A61B5/1455N2
Legal Events
DateCodeEventDescription
Aug 24, 2001ASAssignment
Owner name: CYBRO MEDICAL, LTD., ISRAEL
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:MENDELSON, YITZHAK;REEL/FRAME:012120/0515
Effective date: 20010822