U.S. patent application number 10/524984 was filed with the patent office on 2006-07-06 for capacitive uterine contraction sensor.
Invention is credited to Robert Czarnek.
Application Number | 20060149168 10/524984 |
Document ID | / |
Family ID | 31946765 |
Filed Date | 2006-07-06 |
United States Patent
Application |
20060149168 |
Kind Code |
A1 |
Czarnek; Robert |
July 6, 2006 |
Capacitive uterine contraction sensor
Abstract
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).
Inventors: |
Czarnek; Robert; (Johnstown,
PA) |
Correspondence
Address: |
THE WEBB LAW FIRM, P.C.
700 KOPPERS BUILDING
436 SEVENTH AVENUE
PITTSBURGH
PA
15219
US
|
Family ID: |
31946765 |
Appl. No.: |
10/524984 |
Filed: |
August 19, 2003 |
PCT Filed: |
August 19, 2003 |
PCT NO: |
PCT/US03/26057 |
371 Date: |
January 11, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60404808 |
Aug 19, 2002 |
|
|
|
Current U.S.
Class: |
600/591 ;
600/382 |
Current CPC
Class: |
A61B 2562/02 20130101;
A61B 5/4356 20130101; A61B 5/391 20210101 |
Class at
Publication: |
600/591 ;
600/382 |
International
Class: |
A61B 5/103 20060101
A61B005/103; A61B 5/04 20060101 A61B005/04 |
Claims
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 claim 1, further comprising a conductive standoff
sandwiched between the substrate and the second electrode for
maintaining the second electrode in spaced relation to the first
electrode, the conductive standoff electrically coupled to the
second electrode and electrically isolated from the first
electrode.
3. The sensor of claim 1, wherein the second electrode comprises a
spring mechanism, wherein the spring mechanism is electrically
isolated from the first electrode, the second electrode maintained
in spaced relation to the first electrode.
4. The sensor of claim 3, wherein: 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 claim 1, further comprising a load transfer button
positioned on a side of the second electrode facing away from the
first electrode.
6. The sensor of claim 1, further comprising electronic circuitry
for determining a capacitance of a capacitor formed by the spaced
relation of the first and second electrodes.
7. The sensor of claim 6, further comprising means for
communicating with an external monitoring unit.
8. The sensor of claim 1, further comprising means for securing the
capacitive uterine contraction sensor against an abdomen.
9. The sensor of claim 1, further comprising a dielectric disposed
between the first electrode and the second electrode.
10. The sensor of claim 1, further comprising a conductive sheet on
each side of the substrate, wherein: 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.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates generally to fetal monitoring
apparatuses and, more particularly, to an apparatus for sensing
uterine activity, in particular, contractions.
[0003] 2. Description of the Prior Art
[0004] 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.
[0005] 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.
[0006] Such fetal monitors, however, regardless of their
sophistication, require a device or element to actually sense the
uterine contractions.
[0007] 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.
[0008] 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.
[0009] 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.
SUMMARY OF THE INVENTION
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a perspective view of a first embodiment of a
capacitive sensing element;
[0017] FIG. 2 is an exploded perspective view of the sensing
element of FIG. 1;
[0018] FIG. 3 is a cross-sectional side view of the sensing element
taken along lines III-III in FIG. 1;
[0019] FIG. 4 is a perspective view of the sensing element of FIG.
1 incorporating electronic circuitry;
[0020] FIG. 5 is a cross-sectional side view of the sensing element
of FIG. 4 taken along lines V-V in FIG. 4;
[0021] FIG. 6 is a simplified schematic of the electronic circuitry
of the sensing element of FIG. 4;
[0022] FIG. 7 is an alternate embodiment of the electronic
circuitry of the sensing element of FIG. 4;
[0023] FIG. 8 is an exploded perspective view of a second
embodiment of the capacitive sensing element;
[0024] FIG. 9 is top view of a spring mechanism of the second
embodiment of the capacitive sensing element of FIG. 8; and
[0025] FIG. 10 is a cross-sectional side view of the second
embodiment of the capacitive sensing of FIG. 8 taken along lines
X-X in FIG. 8.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] 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.
[0027] FIGS. 1-3 are views of a first embodiment capacitive sensing
element 10, with FIG. 2 illustrating an exploded view of the
component parts thereof. Sensing element 10 includes a printed
circuit board 12, having a copper top 14, a copper base 16, and an
insulating, e.g., fiberglass, substrate 18. An electrically
isolated stationary electrode 20 is defined in copper top 14 by
removing, e.g., etching, a suitable portion of copper top 14 to
form therein a crevice 26 having as its base an exposed portion of
substrate 18. An exemplary thickness of printed circuit board 12 is
1.6 mm, so as to allow for an appropriate thickness of copper top
14, copper base 16 and substrate 18. An electrode 22 is held in
spaced relation to stationary electrode 20 by a standoff 24
whereupon a gap 25 is created between electrodes 20 and 22.
Desirably, gap 25 is filled with air. However, if greater
sensitivity is required, gap 25 can be filled with a dielectric
fluid or a deformable dielectric solid material. Desirably,
standoff 24 is formed from electrically conductive material.
Alternatively, standoff 24 can be formed from any suitable material
having an electrically conducting coating thereon. Standoff 24 is
configured to be received on copper top 14 in electrical contact
herewith and electrically isolated from stationary electrode 20 by
crevice 26.
[0028] 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.
[0029] When a force is applied to electrode 22 in the direction of
arrow 27 in FIG. 3, electrode 22 will move toward stationary
electrode 20. This movement changes the size of gap 25 and, hence,
a capacitance of a capacitor C formed by electrodes 20 and 22 held
in spaced relation by standoff 24.
[0030] With reference to FIGS. 4 and 5 and with continuing
reference to FIGS. 1-3, slots 30 can be formed through substrate
12, copper top 14 and copper base 16 adjacent to sides or edges of
substrate 12. A belt 38, e.g., an elastic belt, can be threaded
through slots 30 as shown and can be utilized for securing sensing
element 10 against a patient's abdomen. It is to be understood,
however, that slots 30 and elastic belt 38 serve as exemplary means
for securing sensing element 10, and that other means (not shown)
exist, including the use of adhesive materials for securing sensing
element 10 to a patient.
[0031] 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.
[0032] 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.
[0033] FIG. 5 shows electronic circuitry 32 located on a side of
printed circuit board 12 opposite electrode 22. Alternatively,
electronic circuitry 32 can be positioned on the same side of
printed circuit board 12 as electrode 22. In yet another
alternative, electronic circuitry 32 can be situated entirely off
printed circuit board 12, yet still be connected to printed circuit
board 12 through any suitable means including, but not limited to,
electrical lines 33, as shown in FIG. 1. This alternative may be
used when sensing element 10 is considered to be disposable, in
that high-cost and reusable components, such as electronic
circuitry 32, are offboard. Thus, after disposing of one sensing
element 10, electrical lines 33 of another sensing element 10 may
then be reattached to the offboard electronic circuitry.
[0034] With reference to FIG. 6 and with continuing reference to
FIGS. 1-5, electronic circuitry 32 can include a processor 44, a
digital-to-analog converter 45, a reference timer 46, a resistor 47
and capacitor C defined by sensing element 10. In operation,
reference timer 46 outputs a timing signal to processor 44. If gap
25 between stationary electrode 20 and electrode 22 varies, the
capacitance of sensing element 10 will change whereupon the RC time
constant of capacitor C and resistor 47 will also change. Processor
44 is configured to determine the capacitance of sensing element 10
using the RC time constant and the inputted timing signal from
reference timer 46. Processor 44 will then output a digital signal
related to the determined capacitance, which is transformed into an
analog signal by the digital-to-analog converter 45. This analog
signal can then be displayed in an understandable format by
monitoring unit 42 as contraction related information. It is to be
understood that there are, however, several known methods for
measuring capacitance which could be used in accordance with the
present invention. For example, as shown in FIG. 7, sensing element
10 and resistor 47 can be connected to alter the frequency of a
signal output by adjustable frequency timer 46, e.g., a 555 timer,
to processor 44, which is operating at a fixed frequency. In this
embodiment of electronic circuitry 32, processor 44 is configured
to convert the frequency of the signal output by reference timer 46
into a signal indicative of the capacitance of capacitor C.
[0035] 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 FIGS.
8-10 and with continuing reference to FIGS. 1-7, the second
embodiment capacitive sensing element 10' is shown with additional
and substituted components differentiating it from sensing element
10. Essentially, electrode 22 and standoff 24 of capacitive sensing
element 10 are not utilized in capacitive sensing element 10'.
Instead, sensing element 10' includes an electrode having a body in
the form of a disc 52, a plurality of standoffs 53, and a plurality
of mounting pads 54. It is to be understood that the body may be of
any suitable shape, and is shown herein as a disc for exemplary
purposes. Desirably, disc 52 is constructed of beryllium-copper.
However, this is not to be construed as limiting the invention
since the use of any suitable material such as stainless steel or a
copper-clad fiberglass plate is envisioned.
[0036] 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 FIG. 10. When the
force is removed, the spring mechanism moves central portion 57
away from stationary electrode 20 . It is to be understood that
disc 52 is electrically isolated from stationary electrode 20 and
is electrically connected to copper top 14 via standoff 53.
[0037] Load transfer button 40 that is placed on top of electrode
22, shown in FIG. 4, may also be placed on top of disc 52.
Alternatively, a different load transfer button 60 having a stem 61
may be utilized in both sensing element 10 and sensing element 10'.
To this end, as shown in FIG. 8, printed circuit board 12 may
include a hole 62 that extends through a top surface of stationary
electrode 20 and into printed circuit board 12. Additionally, disc
52 includes a centrally situated hole 64. This allows for stem 61
of load transfer button 60 to be received through hole 64 and into
hole 62, resulting in load transfer button 60 abutting disc 52.
Thus, in operation, a force resulting from uterine contraction
applied to load transfer button 60, will cause load transfer button
60 to move disc 52 toward stationary electrode 20. A change in the
size of gap 25 between disc 52 and stationary electrode 20 creates
a change in capacitance of a capacitor formed by disc 52 and
stationary electrode 20 that can be detected and processed by
processor 44. It is to be appreciated that hole 62 guides stem 61
and stabilizes load transfer button 60, thereby preventing
horizontal movement of disc 52 and ensuring accurate measurements
of uterine contractions. If load transfer button 60 is utilized in
sensing element 10, then electrode 22 and stationary electrode 20
necessitate appropriate holes for accommodating stem 61
therein.
[0038] 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.
[0039] 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.
* * * * *