US 20060149168 A1
A capacitive uterine contraction sensor (28) includes an insulating substrate (18), a first electrode (20) disposed on one side of the substrate (18), and a second electrode (22) positioned in a spaced relation to the first electrode (20). The second electrode (22) is configured to move toward or away from the first electrode (20). The sensor may also include a conductive standoff (24) sandwiched between the substrate (18) and the second electrode (22) for maintaining the second electrode (22) in a spaced relation to the first electrode (20). The conductive standoff (24) is electrically coupled to the second electrode (22) and electrically isolated from the first electrode (20). Alternatively, the second electrode (22) may include a spring mechanism used in conjunction with a standoff (24) to maintain the second electrode (22) in a spaced relation to the first electrode (20). The spring mechanism is electrically isolated from the first electrode (20) and enables the second electrode (22) to move toward or away from the first electrode (20).
1. A capacitive uterine contraction sensor comprising:
an insulating substrate;
a first electrode disposed on one side of the substrate; and
a second electrode positioned on the first side of the substrate in a spaced relation to the first electrode, at least part of the second electrode configured to move toward or away from the first electrode.
2. The sensor of
3. The sensor of
4. The sensor of
the second electrode includes a plurality of channels in a body;
a plurality of tabs extend from the body; and each tab is secured to the substrate via a standoff.
5. The sensor of
6. The sensor of
7. The sensor of
8. The sensor of
9. The sensor of
10. The sensor of
the conductive sheets are electrically connected;
the first electrode is electrically isolated from the conductive sheet on the one side of the substrate; and
the second electrode is electrically connected to the conductive sheet on the one side of the substrate.
1. Field of the Invention
This invention relates generally to fetal monitoring apparatuses and, more particularly, to an apparatus for sensing uterine activity, in particular, contractions.
2. Description of the Prior Art
Fetal monitors, which are typically quite sophisticated, are widely used to monitor the uterine activity of pregnant women, as well as the condition of the fetus and the uterus. Analysis of uterine contractions, in conjunction with fetal heart rate, during pregnancy and labor yields significant information concerning the condition of the fetus as well as the advancement of labor. Such monitoring is particularly helpful in so-called difficult pregnancies to systematically evaluate fetal stress, but it is certainly of use in more routine pregnancies as well.
Information of fetal distress will result in prompt remedial action, including a cesarean delivery, both during pregnancy and/or during actual labor. Likewise, early contractions can be treated so as to achieve full-term pregnancies. Examples of currently available fetal monitors include the FetaScan from International Biomedics, Inc., the Corometrics 115, and the Hewlett-Packard 8040A.
Such fetal monitors, however, regardless of their sophistication, require a device or element to actually sense the uterine contractions.
These elements can be intra-uterine or extra-uterine. An example of an intra-uterine sensing element is a catheter which is capable of measuring uterine activity within the uterine cavity itself. Such sensors are disclosed in U.S. Pat. Nos. 4,785,822; 4,873,986; 4,873,990; 4,909,263; 4,942,882; 4,944,307; 4,953,563; and 4,966,161. However, these devices are invasive and therefore they cannot be used for pre-term monitoring.
Other devices, known as tocotonometers, are capable of non-invasively sensing uterine activity and, therefore, are widely used with fetal monitors. Tocotonometers measure the hardness of the abdomen wall, which is an indication of the uterine activity, by various mechanical means. Specifically, tocotonometers include strain gauge elements mounted to an elastic member or are based on LVDT sensors. Tocotonometers are expensive, structurally delicate, i.e., break easily, and are difficult to sanitize between uses. In use, the tocotonometer is held in contact with the abdomen, usually by a belt-like device, in the vicinity of the fundus, i.e., the top of the uterus. The tocotonometer under pre-load by the belt responds with a constant recording level between contractions. The output of the tocotonometer is transmitted to the fetal monitor. Examples of such tocotonometers are manufactured by Huntleigh, Model #447; Corometrics, Model #2260; and Hewlett-Packard, Model #15248A. Other types of mechanical-type sensors for measuring uterine contractions are disclosed in U.S. Pat. Nos. 3,913,563; 4,949,730; 4,966,152; and 4,989,615. Like tocotonometers, these devices are expensive, complicated in construction and use, and difficult to sanitize between uses. The sensor disclosed in U.S. Pat. No. 4,949,730 utilizes a piezoelectric element which cannot measure contractions over a sustained period of time because the charge of the piezoelectric element dissipates quickly, e.g., several seconds.
Accordingly, it is desirable to provide an apparatus for detecting uterine activity which is inexpensive, non-complicated in construction, easy to operate, easy to clean, can be made disposable or reusable, does not decay or electrically drift over time, and/or can be interchanged with presently available fetal monitors. Still other desirable features of the invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description.
The present invention is directed toward an extra-uterine sensing device for directly measuring changes in pressure brought about by uterine contractions of a wearer. The device includes a circuit board, two electrodes, a gap between the electrodes which is filled by air or some other deformable dielectric material, a device to maintain the gap, and a circuit used to measure changes in capacitance.
The first electrode is held stationary with respect to the base, while the second electrode is allowed to move relative to the first electrode. The relevant movement is enabled through the use of a spring mechanism or the elastic deflection of a non-stationary electrode under an applied load. The change in distance between the electrodes varies the gap and, therefore, the capacitance, between the electrodes. If a higher level of sensitivity or a smaller size is required, the gap can be filled with a dielectric fluid or deformable dielectric material. An electronic circuit connects to the capacitive sensing device and properly scales the change in capacitance and outputs the scaled result to a monitor or like device capable of displaying the desired information regarding the strength of the contraction. A shield eliminating the electrical influence of external objects can be placed around the electrodes to further improve the performance of the device.
A minimum pre-load is applied to the sensing device sufficient to establish a reference level of pressure. Once the reference level is attained, the sensing device instantaneously detects changes in the pressure caused by contractions. The changes in pressure are then converted to a change in capacitance and the change in capacitance is then converted to a non-decaying electrical signal which is monitored.
The device can be held against the uterus through a variety of means. These means include an elastic belt, strap, applying adhesive material to the base of the sensing device, or any like method. The belt would be tightened to apply the minimum level of pre-load to the sensing device. Alternatively, a weight can be adapted to rest upon the outer member to apply more force if the belt does not establish the required minimum level of pre-load. A weight could also be utilized to apply the required minimum level of pre-load if the sensing device is held to the uterus through the use of an adhesive material.
The device can be built as an inexpensive disposable unit or can be used as the sensing element in a permanent multiple-use transducer. In a disposable embodiment, the whole transducer can be formed by the technology used to produce multi-layer printed circuit boards where the fiberglass plate typically used as the structural material of the boards is used as the elastic element of the transducer. A calibration resistor or equivalent component can be added to the assembly to assure repeatability from unit to unit. If the electronic circuit is based on a microprocessor chip, then its memory can be used to store the proper calibration constants.
These and other advantages of the present invention will be understood from the description of the preferred embodiments, taken with the accompanying drawings, wherein like reference numerals represent like elements throughout.
The present invention will be described with reference to the accompanying figures, where like reference numbers correspond to like elements. It is to be understood that the attached figures and the following specification are for the purpose of describing the invention and are not to be construed as limiting the invention.
Electrode 22 is electrically connected via standoff 24 to copper top 14 and copper base 16. Copper top 14 and copper base 16 may be connected via any number of suitable means including, but not limited to, a conductively plated throughhole 23. This electrically connected arrangement acts as a ground, and thus forms an electric shield around stationary electrode 20. Desirably, electrode 22 is constructed out of a thin elastic metal plate, such as beryllium-copper or stainless steel. Such a design would assure long-time stability and durability of the product. However, electrode 22 can be formed from any suitable elastic conductive material.
When a force is applied to electrode 22 in the direction of arrow 27 in
With reference to
Alternatively, sensing element 10 may include a load transfer button 40 placed on top of electrode 22 as shown. Load transfer button 40 allows a pre-load to bias electrode 22 toward stationary electrode 20 when elastic belt 38 is tightened around a patient.
Electronic circuitry 32 can be coupled in a suitable manner to a side of substrate 18 having copper base 16 thereon. To this end, a suitable pattern of interconnects (not shown) can be formed, e.g., etched, on copper base 16 in a manner known in the art for receiving electronic circuitry 32. Electronic circuitry 32 converts the capacitance of capacitor C into an electric signal. Where the capacitance of capacitor C changes in response to movement of electrode 22 toward or away from stationary electrode 20, e.g., in response to the onset or end of a uterine contraction, this change causes a change in the electrical signal output by electronic circuitry 32. This change can be output through a cable 34 to a suitable monitoring unit 42 for storage and/or display in an understandable format representing, for example, the rate of contraction and/or other related information. It is to be understood that the electric signal may be communicated to and/or displayed in other ways including, but not limited to, through the use of a wireless transmitter-receiver link. Thus, appropriate modifications known to those having ordinary skill in the art can be made to electronic circuitry 32. This may include adding battery-operated capabilities to sensing element 10.
With reference to
While first embodiment capacitive sensing element 10 utilizes electrode 22 in combination with standoff 24, a second embodiment capacitive sensing element 10′ can utilize an electrode in combination with a spring mechanism. With reference to
Disc 52 includes tabs 55 extending from opposite sides thereof. Additionally, disc 52 includes channels 56, allowing a central portion 57 of disc 52 to move relative to tabs 55. Thus, the arrangement of channels 54 forms a spring mechanism integrated within disc 52. More specifically, each channel 56 defines a pair of fingers 58, each of which extends away from the adjacent tab 55. The fingers 58 coact to form a spring mechanism that enables central portion 57 to move toward and away from substrate 12 when disc 52 is attached thereto. Each standoff 53 is positioned and secured between tab 55 of disc 52 and one of the mounting pads 54 of printed circuit board 12. This causes disc 52 to be disposed in spaced relation to stationary electrode 20, while enabling disc 52 to be moved toward or away from stationary electrode 20 via the spring mechanism. Specifically, when a force in the direction of arrow 27 is applied to disc 52, the central portion 57 moves toward stationary electrode 20 to the position shown in
Load transfer button 40 that is placed on top of electrode 22, shown in
It is to be understood that the general function and operation of second embodiment capacitive sensing element 10′ is similar to that of first embodiment capacitive sensing element 10. Thus, although not explicitly shown, sensing element 10′ can include on onboard or remote electronic circuitry 32. The calculation and transmission of the electric signal in electronic circuitry 32 utilized in sensing element 10′ is also similar. Additionally, sensing element 10′ can be attached to a patient using the same means as described above for sensing element 10.
The invention has been described with reference to the preferred embodiment. Obvious modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.