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DEVICE FOR MEASURING A BLOOD
PRESSURE AND METHOD
This application is a continuation-in-part of U.S. patent application Ser. No. 09/678,650, filed Oct. 4, 2000, issued Jul. 23, 2002, as U.S. Pat. No. 6,423,010, the entire contents of which are incorporated herein by reference.
BACKGROUND OF INVENTION
The invention relates to a physiological-signal-analysis device for measuring a blood pressure, and particularly to a device that applies a pressure to a patient and determines whether a detected pressure oscillation satisfies one or more criteria.
There are many known devices for measuring a patienfs blood pressure. One type of device uses a technique referred to as an oscillometric technique. For this technique, typically, a blood pressure cuff is connected to an arm of the patient and is pneumatically controlled to apply a high pressure to the patient. The pressure is then reduced in steps to a low pressure. For each pressure step (also referred herein as pressure level), a pressure transducer connected with the cuff senses a cuff pressure. The sensed cuff pressure includes the applied pressure and pressure oscillations (also referred to herein as blood pressure oscillations, pressure pulses and blood pressure pulses). The sensed cuff pressure is applied to a control unit that isolates the pressure oscillations and stores two consecutive, matching oscillations at each pressure step. Requiring two consecutive, matching oscillations prevents intermittent artifact from causing the device to seriously err when performing the measurement. Example blood pressure monitors that require two consecutive, matching oscillations are described in RAMSEY M., Blood Pressure Monitoring: Automated Oscillometric Devices, Journal of Clinical Monitoring, 1991, 7 (1), 56-67, which is incorporated herein by reference.
SUMMARY OF INVENTION
The time duration for measuring a blood pressure depends on the magnitude of the high pressure, the difference in pressure between steps, and the amount of time at each step. With the requirement that the device needs to match consecutive oscillations at each level, the blood pressure determination may be unduly prolonged and the patient may be unduly stressed or inconvenienced. The time for each pressure step is established by the time it takes two consecutive cardiac contractions to produce two, roughly equal pressure oscillations in the cuff. For example, if at a particular pressure step first, third, fifth and sixth pulses match while the second and fourth pulses do not, then the step may be unduly long. This is because the prior art system does not proceed to the next pressure step until after the sixth pulse. Accordingly, it would be beneficial to provide a device for measuring a patienfs blood pressure where the device includes criteria that allows two nonconsecutive pulses to be matched at a level.
Additionally, for some embodiments, it is beneficial to provide a device for measuring a patienfs blood pressure where the device relaxes or changes one or more criteria when a known event is occurring. By relaxing one or more criteria, the device allows the measurement to be performed in a timely fashion for some medically unstable patients. Without the relaxed criteria, the measurement may take too long, causing discomfort to the patient and possibly resulting in no blood pressure determination. Relaxing the criteria in a proper fashion will not overly affect the accuracy of the determination.
Accordingly, in one embodiment, the invention provides a method of determining whether an oscillation of a pressure signal acquired from a patient satisfies one or more criteria. The method includes the acts of acquiring a first oscillation
5 having a first fiducial point, acquiring a second oscillation having a second fiducial point, calculating a time interval representing a time from the first fiducial point to the second fiducial point, and determining whether the time interval is a substantial integral multiple of a nominal time interval.
1° In yet another embodiment, the method provides acquiring a first electrocardiogram (ECG) beat having a first fiducial point, acquiring a first oscillation having a relationship to the first ECG beat, acquiring a second ECG beat having a second fiducial point, acquiring a second oscilla
15 tion having a relationship to the second ECG beat, calculating a time interval representing a time from the first fiducial point to the second fiducial point, determining whether the time interval is close to an integral multiple of a nominal time interval, and deciding against selecting the
20 second pressure oscillation when the time interval is not close to an integral multiple of a nominal time interval.
In another aspect of the invention, the invention provides a physiological-signal-analysis device for determining blood pressure values of a patient. The device includes a cuff
25 attachable to an extremity of the patient, a pneumatic system connected to the cuff that supplies a fluid to the cuff, a pressure transducer that captures a pressure signal having pressure oscillations, and a control unit connected to the pneumatic system and the pressure transducer. The control
30 unit is operable to acquire a first oscillation having a first fiducial point, acquire a second oscillation having a second fiducial point, calculate a time interval representing a time from the first fiducial point to the second fiducial point, decide against selecting the second oscillation when the time
35 interval is not a substantial integral multiple of an oscillation period, and calculate a blood pressure value based on selected oscillations.
In a further aspect, the invention provides a software program for operating a physiological-signal-analysis device. The software program includes a pneumatic control module for controlling the operation of the pneumatic system, and an analysis module for analyzing input from the pressure transducer and for calculating a blood pressure. The analysis module includes instructions that are implemented for acquiring a first oscillation having a first fiducial point, acquiring a second oscillation having a second fiducial point, calculating a time interval representing a time from the first fiducial point to the second fiducial point, and determining whether the time interval is close to an integral multiple of a nominal time interval.
Other features, advantages and embodiments of the invention will become apparent by consideration of the detailed description and accompanying drawings.
55 BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic diagram of a physiological-signalanalysis device embodying the invention.
FIG. 2 is a flow chart representing one method of opera60 tion of the physiological-signal-analysis device.
FIG. 3 is a flow chart representing one embodiment for determining whether pressure oscillations satisfy the defined matching criteria.
FIG. 4 is a diagram representing a plurality of pressure 65 oscillations.
FIG. 5 is a diagram representing a plurality of ECG beats and a plurality of pressure oscillations.
Before any embodiments of the invention are explained, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.
A physiological-signal-analysis device 100 is schematically shown in FIG. 1. As used herein, the term physiological-signal-analysis device includes any device that, among other things, non-invasively monitors blood pressure. An example physiological-signal-analysis device 100 is a blood pressure monitor. It is envisioned that the physiological-signal-analysis device 100 may acquire other physiological signals. For example, if the physiologicalsignal-analysis device 100 is a patient monitor, then the patient monitor may acquire other physiological signals such as a patienf's ECG, a patienf's respiratory function, etc. Unless specified otherwise, the physiological-signalanalysis device 100 is a blood pressure monitor.
In general terms, the device 100 includes a cuff 105, a pneumatic system 110, a pressure transducer 120, a control unit 125, one or more operator-controlled input devices 130, and one or more output devices 135. The cuff 105 is any conventional inflatable cuff connected to the pneumatic system 110. As used herein, the term "connection," and variations thereof (e.g., connect, connected, connecting, etc.), includes direct and indirect connections. The connection, unless specified, may be by mechanical, electrical, chemical, and/or electro-magnetic means, or any combination of the foregoing (e.g. electro-mechanical). For the embodiment shown, the cuff is mechanically connected to the pneumatic system 110 via one or more tubes.
The pneumatic system 110 includes a pump 140 that pumps a fluid (e.g., air) to the cuff 105. The pressure transducer 120 is connected to the cuff 105 and measures a cuff pressure in the cuff. Typically, the pressure transducer measures the cuff pressure with an additional small varying component (in this case, pressure oscillations) caused by the arterial blood pressure pulsation of a patienf's arm.
In some embodiments, the device 100 may further include other physiological-signal-input devices 150 (shown in phantom) such as other transducers or sensors. For example, the sensors may include ECG electrodes, pulse-oximetry sensors, temperature sensors, etc.
As shown in FIG. 1, the control unit 125 receives input signals from the pressure transducer 120, the other sensors or transducers 150 (if present), and the one or more operatorcontrolled input devices 130. The input signals include input or data. The control unit analyzes the inputs, and communicates output signals to the pneumatic system 110 and the output devices 135. The output signals include output or data. The control unit 125 includes an analog-to-digital converter 152, processor 155 and a memory 160. The memory 160 includes one or more software modules having instructions, and the processor 155 retrieves, interprets, and executes the instructions of the one or more software modules to control the device 100. Example software modules include a pneumatic system control module for controlling
the pneumatic system, and an analysis module for analyzing the input from the pressure transducers and/or the physiological-input devices and for calculating a blood pressure (e.g., systolic pressure, diastolic pressure, mean
5 arterial pressure, etc.). Other software modules will become apparent from the description below.
In general, the software modules stored within the memory 160 instruct the control unit to receive the inputs from the pressure transducer 120, the one or more
10 physiological-signal-input devices 150 (if present), and the one or more operator-controlled input devices 130; to analyze the received inputs; and to provide outputs to the pneumatic system 110 and the one or more output devices 135. The operation and control of the device 100 is discussed in more detail below.
For the embodiment described herein, any processor 155 capable of reading, interpreting and executing software instructions is used with the invention. However, it is envisioned that other processors or controllers may be used
2Q with the invention. For example, the processor may be constructed with other analog and/or digital logic circuitry, and may include integrated and/or discrete circuit elements. Also, the control unit 105 may include other elements (e.g., one or more analog-to-digital converters, one or more
25 drivers, one or more power supplies, one or more amplifiers, one or more filters, etc.) that would be apparent to one skilled in the art to support the control unit 125.
The one or more operator-input devices 130 allow an operator (e.g., a technician, nurse, doctor, etc.) to control the
30 device 100 and/or to provide data to the control unit 125. Example operator-input devices 130 include one or more push buttons, one or more trim knobs, a keyboard, a keypad, a touch screen, a pointing device (e.g., a mouse, a trackball), or similar devices. Further and for some aspects of the
35 invention, the one or more operator-controlled input devices 130 may include data storage devices, and other devices or processing units connected via a network. Of course, not all of the operator-controlled input devices 130 are required for operation of the device 100.
40 The one or more output devices 135 allow the control unit to communicate outputs or data to the operator. Example output devices 135 include a printer, a display (e.g., an LED display, an LCD display, a CRT display, etc.), a storage device (e.g., a magnetic-disc drive, a read/write CD-ROM,
45 etc.), a server or other processing unit connected via a network, audio-output devices, and similar devices. Of course, not all of the output devices 135 are required for operation of the physiological-signal-analysis device 100. Also, the one or more output devices 135 and the one or
50 more operator-controlled input devices 130 may be combined as a single device (i.e., a touch screen).
As shown in FIG. 1, the pneumatic system 110, the pressure transducer 120, the control unit 125, the operatorcontrolled input devices 130 and the output devices 135 are
55 secured within a central unit 165. However, one skilled in the art will realize that the one or more elements of the monitor 100 may not be secured within the central unit 165. For example, the operator-controlled input device 130 may be a keyboard or keypad that is connected externally to the
60 central unit 165. Thus, the device 100 may be a system incorporating one or more sub-units. As used herein the terms physiological-signal-analysis device and blood pressure monitor encompass units having a number of components, or systems incorporating more than one dis
65 tinct device.
In operation, the cuff 105 is wrapped around a patienf's arm and an operator initiates a test by depressing an input