WO1999019704A1 - Capteurs de pression a semi-conducteur noye, tocodynamometres - Google Patents

Capteurs de pression a semi-conducteur noye, tocodynamometres Download PDF

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Publication number
WO1999019704A1
WO1999019704A1 PCT/US1998/018070 US9818070W WO9919704A1 WO 1999019704 A1 WO1999019704 A1 WO 1999019704A1 US 9818070 W US9818070 W US 9818070W WO 9919704 A1 WO9919704 A1 WO 9919704A1
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WO
WIPO (PCT)
Prior art keywords
force
housing
pressure sensor
pressure
sensor
Prior art date
Application number
PCT/US1998/018070
Other languages
English (en)
Inventor
Patrick R. Roycroft
Steven T. Saville
Original Assignee
Novatrix, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Novatrix, Inc. filed Critical Novatrix, Inc.
Priority to AU92972/98A priority Critical patent/AU9297298A/en
Publication of WO1999019704A1 publication Critical patent/WO1999019704A1/fr

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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/03—Detecting, measuring or recording fluid pressure within the body other than blood pressure, e.g. cerebral pressure; Measuring pressure in body tissues or organs
    • A61B5/033—Uterine pressure
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/43—Detecting, measuring or recording for evaluating the reproductive systems
    • A61B5/4306—Detecting, measuring or recording for evaluating the reproductive systems for evaluating the female reproductive systems, e.g. gynaecological evaluations
    • A61B5/4343—Pregnancy and labour monitoring, e.g. for labour onset detection
    • A61B5/4356—Assessing uterine contractions
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/02—Details of sensors specially adapted for in-vivo measurements
    • A61B2562/0261—Strain gauges
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
    • A61B5/7235—Details of waveform analysis
    • A61B5/7242—Details of waveform analysis using integration

Definitions

  • the invention generally relates to the field of pressure sensors, and specifically to a pressure sensor including a solid state force sensor embedded within a protective housing which senses a force received from the exterior surface of the housing when the housing presses against a body.
  • a normal labor process is divided into three stages. Among these stages, the first and second stages are the crucial ones which are directly involved in the delivery of fetus.
  • the first stage of labor begins with the onset of rhythmic uterine contraction and ends at the complete dilation of the cervix which is about 1 0 cm in diameter.
  • the complete dilation of the cervix marks the beginning of the second stage of labor which ends immediately after the birth of the fetus.
  • the third stage of labor extends from the birth of the baby to the complete expulsion of the placenta.
  • the labor progress is driven by two types of labor forces.
  • the primary force is produced by the involuntary contractions of uterine muscle.
  • the secondary force is produced by the increase of intra-abdominal pressure through voluntary contractions of the abdominal muscles and diaphragm. These forces cause an increase of intrauterine pressure to provide a critical expulsion force on fetus.
  • oxytocin infusion is commonly used in clinical practice to increase the primary labor force by directly inducing uterine contraction.
  • Other pharmaceutical methods of induction are known, including the use of dinoprosten and progesterone antagonist (RU-486), however, oxytocin has been found to have the fewest adverse side effects.
  • Clinical evidence has demonstrated that oxytocin alone can only partially solve the problem of prolonged labor and dystocia associated with epidural anesthesia. However, a high incidence of cesarean section still occurs in patients receiving epidural anesthesia in spite of a high dosage of oxytocin infusion.
  • oxytocin If the onset of labor is induced using oxytocin because spontaneous labor has not occurred, there is actually an increased cesarean risk compared with patients who labor spontaneously. Furthermore, high doses of oxytocin have been implicated in uterine tetanus and in some adverse neonatal outcomes, including fetal asphyxia. Therefore, continuous fetal monitoring is necessary when pharmaceuticals are used for uterine hyperstimulation to monitor the fetal response to labor and the uterine response to the inducing agent.
  • an inflatable bladder fits over and around the woman's abdomen and is manually inflated and deflated in coordination with the patient's voluntary muscle contractions during the second stage of labor. This device applies pressure equally to the entire abdomen.
  • the Chinese patent of Fei Chao (Chinese Patent No. 21 98, issued in 1 989) teaches an abdominal girdle which has a generally triangular bladder (to match the rough contour of the uterus) which is placed over the patient's abdomen.
  • the bladder is inflated manually in coordination with the woman's contractions to apply a downward pressure on the abdomen, assisting in forcing the fetus downward. While the girdle itself is very effective, the manual control of the inflation/deflation may not be easily accepted by physicians who may be reluctant to rely on a device which could be easily subject to human error with serious consequences.
  • the guard-ring tocodynamometer which was developed in the 50's by Smyth, et al., includes a resistance strain gauge supported within a rigid ring. This device has been identified as the only pressure sensor that externally provides an absolute estimation of the intra-uterine pressure. (See, e.g., C.
  • multiple sensors are usually placed on the patient's abdomen, e.g., for measuring intra-uterine pressure, fetal heart rate and fetal movement.
  • the belts used to hold the rigid sensors in position must be wide and tight enough to provide stability. This increases patient discomfort, and the abdominal area can quickly become covered with various monitoring devices, so that it may become difficult to place every sensor at its ideal position, detracting from the accuracy of the monitoring.
  • existing tocotransducers are sensitive to environmental factors such as humidity and temperature, requiring frequent calibration, and have limited force ranges and maximum ' tolerances, such that the sensors can become saturated, . or even be subject to failure, if not properly positioned and tensioned against the patient's skin.
  • a commonly-used tocotransducer sold by Hewlett-Packard has a maximum tolerance of about 1 kilogram (2.2 pounds) before failure.
  • a similar device sold by Huntleigh has a range of approximately 1 00 grams and a maximum tolerance of about 320 grams (0.7 pounds) .
  • the semiconductor sensor of Garabedian, et al. utilizes conventional MOS (metal-oxide-semiconductor) fabrication techniques to form MOGFETs (MOving Gate Field Effect Transistors) and MOPCAPs (MOving Plate CAPacitor).
  • MOS metal-oxide-semiconductor
  • MOGFETs MOving Gate Field Effect Transistors
  • MOPCAPs MOving Plate CAPacitor
  • a flexible gate structure in the transistor spans a cavity, the bottom of which is an active region. Flexion of gate structure due to external pressure modifies the channel length to provide an electrically measurable change.
  • the top plate spans a cavity, the bottom of which is the other plate. The capacitance varies with flexion of the top plate, which variations are detected.
  • Another solid state pressure sensor is disclosed in U.S. Patent No.
  • This sensor is "ultraminiature" and is designed for use medical application for use in catheters and implantable devices. Such devices are very small, intended to detect minute variations in pressure with a small range, and are costly to manufacture.
  • an embedded semiconductor pressure sensor for externally sensing the pressure within a body includes a housing having an exterior surface and an interior cavity. Means disposed on the exterior surface of the housing transfers force from the exterior surface to the interior cavity when the housing is pressed against the body.
  • a solid state force sensor is located within the interior cavity of the housing adjacent to the means for transferring force. The solid state force sensor receives the transferred force, detects the force and generates an electrical signal representative of the force.
  • an embedded semiconductor pressure sensor for externally sensing the pressure within a body includes a housing having an exterior surface, an interior cavity and means for attaching a pressure- applying device.
  • the housing is formed from a pliable material so that the housing substantially conforms to the body when pressed against the body by the pressure-applying device.
  • a button disposed on the exterior surface of the housing transfers force from the exterior surface to the interior cavity. The button is positioned to press against the body when the housing is pressed against the body.
  • a solid state force sensor located within the interior cavity adjacent to the button is encased within a package having a movable piston in communication with the button to transfer force from the exterior surface to the solid state force sensor. The force sensor detects the force and generates an electrical signal corresponding to the force.
  • an intra-uterine pressure sensor generates an electrical signal indicative of a contraction in a patient for use with a controller for regulating air pressure in an inflatable girdle for supplementing secondary labor force.
  • the pressure sensor includes a housing formed from a pliable material which has an exterior surface and an interior cavity. Means disposed on the exterior surface of the housing transfers force from the exterior surface to the interior cavity. A solid state force sensor is embedded within the interior cavity adjacent to the means for transferring force for receiving the transferred force.
  • the force sensor has a piezoresistive means for detecting the force and generating an electrical signal corresponding to the force.
  • the pressure sensor further includes means for applying pressure to the housing so that the pliable material deforms to substantially conform to the patient's abdomen.
  • Figure 1 is a block diagram of function of the childbirth assisting system of the present invention
  • Figure 2 is a plot of pressure versus contraction duration
  • Figure 3 is a block diagram of the components of the invention
  • Figure 4 is a block diagram of the pressure feedback loop of the prototype system
  • Figure 5 is a diagrammatic front view, partially cut away, of a first embodiment of the girdle for use with the present invention
  • Figure 6 is a side elevation of a second embodiment of the girdle
  • Figure 7 is a diagrammatic front view of a third embodiment of the girdle
  • Figure 8 is a perspective view of a fourth embodiment of the girdle;
  • Figure 9 is diagrammatic side elevation of an alternate embodiment of the bladder/sensor combination;
  • Figure 1 0 is an exemplary plot of an indication of backpressure for assuring single use
  • Figure 1 1 is a perspective view of a solid state tocotransducer for use in detecting intra-uterine pressure
  • Figure 1 2 is a circuit schematic of an equivalent circuit for the piezoresistive force sensor for use in the solid state tocotransducer
  • Figure 1 3 is a diagrammatic view of the piezoresistive force sensor for use in the solid state tocotransducer.
  • Figure 1 4 is a cross-sectional view taken along line 1 4-1 4 of Figure 1 3.
  • Figure 1 is a block diagram of the childbirth assisting device including a patient and a uterine contraction monitor 2.
  • a closed loop system uses patient response and rule-based decision making methods to achieve operator specified responses.
  • the inventive device is a pneumatic closed loop system which is composed of an abdominal girdle 3 and a controller 1 .
  • the controller 1 possesses five main functions:
  • the uterine contraction activity can be monitored either internally or externally.
  • Internal pressure monitoring provides the most accurate assessment of uterine activity by allowing pressure changes in the uterus to be transmitted via a fluid-filled- catheter to a strain gauge transducer. This produces quantitative readings of the duration, frequency, and amplitude of the uterine contraction, as well as the baseline tone of the uterus.
  • An external tocodynamometer can be applied easily at any stage of labor to provide a non-invasive method of assessing uterine contractions. This yields a good estimate of frequency of the contractions but a less accurate indication of the beginning, end and duration of the contraction, and the intensity.
  • the actual amplitude of the contraction is difficult to measure by this method using conventional tocotransducers.
  • an internal pressure monitor 2 may be used for actual amplitude measurement.
  • the internal pressure monitor provides the accurate intrauterine activity data to the controller, which are necessary for improving the safety and efficiency of inventive device.
  • intra-uterine pressure monitoring is externally provided by a solid state force sensor embedded in a solid housing, as shown in Figure 1 1 .
  • the tocotransducer 1 60 includes force sensor 1 62 with a force-transferring face 1 64 which is positioned on housing 1 66 so that force can be transferred to the force sensor 1 62 when the monitor is in position.
  • Force sensor 1 62 is a piezoresistive semiconductor device constructed in accordance with the disclosure of U.S. Patents 5,576,251 and 5, 578,843. These devices are sold commercially under the trade name SenSym.
  • An equivalent circuit of the SenSym force sensor is provided in Figure 1 2, which shows the actual integrated circuit sensor element 1 80, the compensation network 1 82 and amplifier 1 84.
  • External force is transferred to sensor element 1 80 by a piston 1 86 built into plastic package 1 88, as shown in Figures 1 3 and 1 4.
  • Face 1 64 is positioned adjacent to the interior surface of the housing so that the external force can be transferred to piston 1 86.
  • a spring 1 85 and protective disk 1 87 are located over piston 1 86 so that they are in constant contact with each other.
  • Protective disk 1 87 which provides the contact point for transfer of force from button 1 72 to sensor element 1 80, is substantially rigid, and may be formed of metal or a rigid plastic similar to that used for package 1 88.
  • Spring 1 85 may be a conventional compression spring, or may be formed from a compressible, resilient elastomer which may be attached via an adhesive or other attachment means, or pre-loaded to the bottom of protective disk 1 87 and to the outer face of piston 1 86.
  • Button 1 72 is made of the same material and molded at the same time as the housing, or may be rigid plastic attached via adhesive or other attachment means to the outer surface of the housing.
  • the force sensor 1 62 has a range of 800 grams with a maximum tolerance of 1 .8 kilograms (4 lbs). These devices are accurate and stable over a 5-50 degree C temperature range.
  • the 5V operating voltage for the force sensor may be provided by a single D.C. power supply up to + 1 2V.
  • Force sensor 1 62 is completely embedded within housing 1 66, which is preferably an elastic and pliable elastomer. In the preferred embodiment, silicone having a Shore hardness of about 60 durometer is used. Other soft rubber-like materials may also be used.
  • Housing 1 66 may be molded in two parts, top portion 1 67 and bottom portion 1 69.
  • a cavity 1 74 with a channel for a connection wire is formed on its inside surface for receiving the sensor.
  • Cavity 1 74 should be dimensioned to closely fit the exterior of force sensor 1 62 so that it is firmly held in place.
  • a filler such as potting material may be used to hold the sensor within the cavity.
  • Bottom portion 1 69 has a protruding button 1 72 on its exterior surface at a position corresponding to the location of face 1 64 when force sensor 1 62 is in place. Button 1 72 contacts the patient's abdomen and transfers force from the abdomen to face 1 64 for detection by force sensor 1 62.
  • button 1 72 is preferably semi-spherical to provide a focusing function, other shapes may be used as well.
  • the size of button 1 72 has been determined to have an effect on the performance of the device. Tests were performed comparing a small button ( 1 5 mm (0.6 in.) dia. x 6 mm (0.25 in.) high), a medium button ( 1 7 mm (0.7 in.) dia. x 7 mm (0.28 in.) high), and a large button (24 mm (0.93 in.) dia. x 9 mm (0.32 in.) high), each being semi-spherical. While the large button had greater sensitivity, the small button exhibited the lowest signal-to-noise ratio (SNR) . (SNR was determined by calculating the power spectrum of collected signal data, integrating the power spectrum over 60 seconds (signal) and dividing by the integral of the power spectrum under 60 seconds (noise).) The small button was also found to be most comfortable to the patient.
  • SNR signal-to
  • Force sensor 1 62 is sealed within the housing by vulcanizing or otherwise attaching top portion 1 67 to bottom portion 1 69.
  • Connector 1 70 is protected during the assembly process so that, after the housing is sealed, it remains accessible for attachment of a cable connection to the monitor/controller.
  • By completely sealing the sensor within housing 1 66 it is isolated from environmental factors, such as humidity which effect the performance of traditional tocotransducers, and is protected from damage caused by mishandling or dropping the device.
  • the package 1 88 of the force sensor itself provides corrosion resistance and isolation from external package stress, making the solid state tocotransducer robust.
  • housing 1 66 is approximately 1 0.2 cm (4 in.) wide by 7.62 cm (3 in.) high by 1 .3 cm (0.5 in.) thick ( 1 .9 cm including button 1 72.) Housing 1 66 should be sufficiently pliable to conform to the patient's abdomen. This enhances the comfort as well as assuring that the button 1 72 is uniformly pressed against the abdomen.
  • a belt 1 90 (indicated with dashed lines) is used to hold housing 1 66 in position. Slots 1 68 are provided on the sides of housing 1 66 through which the belt is fastened.
  • the belt may be nylon webbing or a soft, elastic fabric to enhance patient comfort, and may be attached by conventional fasteners such as buckles, snaps, or hook-and-pile fasteners.
  • housing 1 66 The forces applied by the belt inserted through slots 1 68 allow housing 1 66 to flex to conform to the patient's abdomen to facilitate uniform application of pressure.
  • the relative thinness of the housing 1 66 compared with prior art tocotransducers provides the option, if necessary, of locating the contraction sensor beneath the girdle of the labor assisting system (between the girdle and the abdomen) without significantly compromising the patient's comfort.
  • the need to position the sensor directly over the fundus for greatest accuracy is sometimes complicated by the size and weight of both the patient and the fetus, and such flexibility in placement of the sensor is advantageous.
  • a stiffening material around the perimeter of housing 1 66 and slots 1 68, since excessive flexibility may damage the seal between sensor 1 62 and housing 1 66, or may actually cause sensor 1 62 to break.
  • An exemplary material is a metal wire or band, or plastic bars, bands, or strands, which are flexible to a lesser degree that the housing material itself. This stiffening material is preferably embedded in one or both halves during the molding process and, thus, will not be visible, leaving a smooth exterior surface.
  • the solid state tocotransducer used in conjunction with the inventive system provides a number of advantages over conventional tocotransducers, including accuracy, robustness, durability and patient comfort.
  • the solid state tocotransducer is likely to cost less than the widely-used guard ring tocotransducers due to the decreased labor costs for manufacture.
  • the inventive system may operate on an open loop principle which comprises a modification of functions 2 and 3 listed above.
  • open loop system application and release of girdle pressure need not rely on intrauterine pressure. Instead, application of pressure to the girdle will be triggered by detection of contraction pressure by the external toco sensor only, and only after a pre- determined threshold pressure is attained and held for a specified period of time. Once inflated, the girdle pressure is maintained for a fixed duration, e.g., 30 seconds, after which the release valve is automatically opened to deflate the girdle.
  • the embodiment of Figure 4 is an exemplary open loop system.
  • the normal uterine contraction curve is bell-shaped, as shown in Figure
  • an average increase in maximum uterine pressure above basal level is about 20 - 30 mmHg while at the active phase, with cervical dilation from 3 cm to 1 0 cm and the second stage of labor, it is in the range of 40 - 50 mmHg.
  • Contraction frequency also increases from two to three per 1 0 minutes to four to five per 1 0 minutes at the end of labor.
  • the controller evaluates the uterine activity data and determines the onset of contraction. Once the controller 1 detects the onset of contraction, the girdle pressure will be increased.
  • Determining the onset of contraction is somewhat arbitrary. This invention may not be recommended for use during the early first stage of labor including the early active phase (cervical dilation up to 6-7 cm) .
  • the onset of contraction is set at 1 5-20 mmHg above the basal level.
  • the girdle pressure is increased at the preset rate until the preset intrauterine pressure is obtained. Once the intrauterine pressure reaches the preset pressure, the girdle pressure will be maintained to obtain a constant intrauterine pressure.
  • the offset of contraction can be detected when the girdle pressure increases sharply, as shown in Figure 2. The girdle pressure will be released upon detection of the offset of contraction.
  • the girdle 3, illustrated in detail in Figure 5, is formed of two basic components: the belt 100 and the bladder 102.
  • the design of the belt requires two considerations.
  • the inner lining must be soft and comfortable to the mother while the outer lining must have high tensile strength so that it can be tightly secured around the mother to keep the bladder inflation pressure downward against the abdomen.
  • the belt 1 00 may be formed from polyvinyl chloride (PVC) or an elastomer-coated fabric, such as polyurethane- coated nylon.
  • the interior lining of the belt which comes in contact with the skin should be a soft fabric, such as the loop material of a hook-and-loop fastener, velour, woven fabric such as cotton or nylon, netting, or a combination of materials including a laminate.
  • a soft fabric such as the loop material of a hook-and-loop fastener, velour, woven fabric such as cotton or nylon, netting, or a combination of materials including a laminate.
  • the choice of materials will depend on the integration of the bladder.
  • the belt could serve as the reinforced lining to the bladder, or it could be part of the bladder.
  • An elastomer coating on outer layer of the belt may be added to prevent the fabric from stretching, or the outer surface may be non-stretch cotton fabric or surgical tape.
  • the belt is originally formed in two layers 1 01 and 1 03 so that the bladder 1 02 may be inserted between the layers.
  • Layer 1 01 represents the outer PVC layer and layer 1 03 represents the inner fabric-lined layer.
  • the layers may be sealed together after the bladder is inserted to firmly retain the bladder at a fixed position within the belt.
  • the sealing welds 1 05 are indicated as dashed lines.
  • the bladder 1 02 may be floating, sealed to only one of the two layers of the belt, or unattached to either layer and simply retained between the two layers once they have been sealed together.
  • Selection of belt configuration may be made based upon pressure transfer efficiency, with the floating bladder version having demonstrated improved pressure transfer in prototypes of the invention. The choice of material of which the belt is made will depend upon whether the bladder is attached or floating.
  • the inner and outer layers will depend upon whether the bladder is attached or floating.
  • 1 01 ' and 1 03' are sealed together without placing the bladder between the layers.
  • the bladder 102 is held directly against the mother's abdomen, with the inward force of the belt providing means for maintaining the bladder in the proper location.
  • Belt tension is critical to the performance of the belt.
  • the end of the belt may be split to form two separately adjustable straps 1 04 and 1 06, as shown in Figure 5.
  • Strips of Velcro ® , or a similar hook-and-pile fastener 1 1 0, are sewn onto end 1 08 of the belt and onto the ends of straps 1 04 and 1 06.
  • the split design allows for the closest possible fit.
  • the fastener on straps 1 04 and 1 06 should have sufficient length to adjust the belt diameter as needed for a particular patient.
  • finger loop 1 09 is formed in end 1 08 to provide an anchor for medical personnel to use while pulling the straps to the desired tension.
  • the loop 1 09 may be formed by doubling over a small portion of the belt material, then welding it in place. Due to the significant amount of monitoring equipment that is used during a delivery, it may become difficult to place certain sensors on the patient's abdomen in conjunction with the belt 1 00.
  • One method for alleviating this is by providing tabs 1 1 2 and 1 1 4 at the lower edge of the belt 1 00 which permit attachment of the toco sensor directly to the belt, eliminating the need for an additional toco belt.
  • the toco sensor 1 1 6, which monitors the contractions, may be mounted on an elastic fabric 1 1 8 with eyelets 1 20, 1 21 , adhesive strips, hook-and-pile fasteners or snaps at either end which. attach to corresponding fasteners 1 22, 1 23 on tabs 1 1 2, 1 1 4.
  • eyelets 1 20, 1 21 since the tabs 1 1 2, 1 1 4 are at a fixed distance ( 1 7.5" in the preferred embodiment), this provides a further advantage in that the toco sensor is always maintained at the same tension against the mother's abdomen.
  • adjustable straps may extend inward from tabs 1 1 2, 1 1 4, the width of the straps being adapted for insertion through slots 1 68.
  • the expandable bladder 1 02 may be formed from a thin reinforced polyurethane, polyvinyl chloride (PVC), silicone, or similar elastomeric membrane material.
  • PVC polyvinyl chloride
  • Inflation nipple 1 28 extends from bladder 1 02 through an opening in the belt 1 00.
  • the material of which the preferred embodiments of the belt and bladder are made are selected to permit the girdle to be. economically manufactured as a single-use, disposable item.
  • the inflation nipple 1 28 can include means for assuring that a girdle is used only once.
  • the single use means can be a break seal/plug incorporated into the inflation nipple 1 28 which, once connected to the monitor and air supply hoses must be broken to remove it, preventing its reuse.
  • Other means for assuring single uses of the girdle can be a peel away connector in the inflation nipple 1 28, a piezo film, or a rupture film built into the nipple 1 28.
  • the rupture film 1 29 (shown diagrammatically as dashed lines in Figure 5) spans the interior of the nipple 1 28 and works in cooperation with the controller 1 .
  • the sense valve 9 will detect a backpressure and the controller 1 will have stored data regarding a pre-set pressure threshold value at which rupture of the film should occur. If the threshold backpressure is not attained, this may be an indication that the film 1 29 was already ruptured in a previous use of the girdle. Software within the controller 1 will prevent any further use of the system until a new girdle is detected by way of the proper backpressure.
  • An exemplary plot of detection of a seal by backpressure showing hypothetical upper and lower limits (UL and LL) for as thresholds for confirming correct backpressure and time to rupture is provided in Figure 1 0.
  • a piezo film would function in a similar manner, with the film, itself, providing the signal indicative of the pressure being applied during the initial burst.
  • an electrically conductive strip could be built into the nipple 1 28 which can be detected by causing a change in resistance of electrical wiring built into the air tubing.
  • a second alternate solution to working within the limited space is to form the bladder with fan-folds 1 32 or accordion pleats, as illustrated in Figure 7.
  • the bladder when the bladder is deflated it covers only a small area of the abdomen.
  • the bladder Upon inflation, the bladder expands within the belt into the area indicated by dashed lines 1 36 to apply pressure in the appropriate direction.
  • a pocket within the belt controls the direction of expansion of the bladder to assure that the pressure is dispersed uniformly and in the proper direction.
  • the bladder is inflated, the readings from the toco sensor are not as critical, so expanding the bladder over the toco sensor is not a problem.
  • the girdle may also incorporate one or more separate bladders 1 40 which are controlled independently of the primary labor-assisting bladder 1 02 to regulate overall belt pressure and to add lumbar support.
  • This embodiment is shown in Figure 8.
  • the primary bladder 1 02 is shown in a slightly different configuration from the typical triangular shape.
  • the shape of the primary bladder is not limited to a triangle, nor must the size be fixed. It can be varied as needed to apply the desired pressure appropriately.
  • Secondary bladders 1 40 help reposition the patient during periods of discomfort. Inflation of bladders 1 40 can be coordinated with contractions to alleviate lower back pain associated with the contractions, or inflation can simply occur at fixed intervals to provide a massaging function.
  • Bladders used for regulating belt tension can alleviate pressure from the epidural and spinal column, making belt application easier.
  • the sensor for detecting contraction and fetal heartbeat may be incorporated into the girdle as described above in the form of a toco sensor, or may utilize ultrasound, pressure sensitive ink or piezo film 1 50, which may be incorporated into the fabric of the belt or in the bladder 1 52 (see Figure 9), or air/fluid displacement.
  • the piezo film 1 50 may be polyvinylidene fluoride (PVDF), which transducers are known in the art.
  • FIG. 1 is a block diagram of automatic labor assisting device, showing the details of the controller 1 and the girdle 3 according to the present invention.
  • a pressure sensing means including pressure transducer 1 1 and analog signal conditioner 1 2, produces a signal which is fed into the microprocessor 22.
  • the signal is quantized in a 1 2 bit analog-to-digital converter within the microprocessor 22.
  • a display means which includes a memory and signal processing circuitry within the microprocessor 22 and display 1 3, produces a pressure display of the girdle's internal pressure.
  • a memory 40 within the controller provides storage for control parameters and a library of diagnostic information, which is described below in more detail.
  • An inflatable girdle 3 is shown connected via tubing 24A and 24B to the controller 1 at coupling 25A and 25B. Coupling 25B is connected via valve 9 and pressure line 26 to pressure transducer 1 1 .
  • a signal representing the pressure measured by the pressure transducer 1 1 and analog signal conditioner 1 2 is applied via electrical line 27 to microprocessor 22.
  • Two of the control switches 1 5 are used to apply a signal to microprocessor 22 to set a target intrauterine pressure and a maximum girdle pressure.
  • a signal representing intrauterine pressure is applied to microprocessor 22 via connector 28 and electrical line 29.
  • Microprocessor 22 is programmed to calculate the girdle pressure adjustment proportional to the magnitude of the difference between the intrauterine pressure and the selected target pressure, and produces an output signal on line 30 which indicates the girdle pressure adjustment.
  • a select switch in control switch 1 5 determines if an external air line via air line 42, an internal replaceable air bottle via air line 21 , or an internal motor 5 and pump 6 are to be used to inflate the girdle. Note that all three air paths are isolated from each other via check valves 1 8, 1 9 and 32.
  • the motor 5 is turned on and off by the microprocessor 22 via line 31 to a motor and valve driver circuit 4.
  • the pressure to the girdle 3 is controlled by the regulator 1 7.
  • Valve 7 vents the pressure in girdle 3 via vent 8 for a time determined by microprocessor 22 through line 52.
  • a voltage regulator 36 provides a 5 volt regulated voltage which is used to power the portion of the digital circuit requiring a positive 5 volts.
  • the 1 2-volt voltage output is also provided for portions of the circuitry such as the valves, pumps and pressure transducer which require 1 2-volt power supply.
  • Differential pressure switches 44 are connected between lines 37A and 38B. If any obstruction occurs between lines 37A and 37B, switches 44 apply a. signal to microprocessor 22 through line 38 to sound an alarm.
  • the microprocessor 22 utilizes the information and the signals applied to it to control the girdle 3 and to provide information output. Signals applied from microprocessor 22 to the displays 1 3 and printer 1 6 include:
  • the microprocessor 22 compares the input signal received from the intrauterine monitor and the girdle pressure sensors against criteria which are stored in the memory 40. These criteria include the various pressure settings, as well as means for identifying the presence of abnormal contractions which may require modification of the operating parameters of the controller or may require removal of the girdle.
  • Sense valve 9 is connected between girdle 3 and pressure transducer 1 1 .
  • the sense valve 9 connects the pressure transducer 1 1 to atmosphere through vent 1 0 during the girdle start-up sequence in order to correct the pressure transducer zero offset.
  • Overpressure valve 39 is connected to the line 50 between regulator 1 7 and mflate-deflate valve 7. This is a manually adjustable valve which limits the maximum pressure delivered to the girdle, in the event that all the safeguards in the air regulation line systems fail.
  • safety valve 23 is designed into the girdle 3 to deflate the girdle in case of extreme overpressure which would endanger the fetus.
  • a prototype of the controller was designed with two feedback control loops.
  • the first loop monitored and evaluated the activity of the uterine contraction.
  • Intrauterine pressure was detected by a strain gauge operated with a bending beam mechanism.
  • the output signal of the strain gauge ranged from 1 V at zero pressure to 5V at 1 05g of force.
  • the signal generated by the strain gauge was digitized and transferred to the built-in microprocessor.
  • the programming within the microprocessor caused the second feedback loop to be initiated once the intensity of the contraction reached a certain point (20% of full scale) and stayed over that point for 5 seconds. Using this criteria, a false signal generated by non-contraction processes such as physical movement by the patient could be filtered out.
  • the second feedback control loop shown in Figure 4, controlled the inflation and deflation of the girdle 3 using an air compressor 60.
  • This loop is a slight modification of the system of Figure 3.
  • the girdle is connected to the air compressor 60 (Gast Manufacturing Corp. diaphragm compressor, 50 PSI maximum with 1 5 cubic inches per second air flow) through air line 80 with air valve 67 controlling the rate of inflation of the girdle 3.
  • the girdle 3 may be deflated through air line 82 by opening air valve 77 and venting the girdle to atmospheric pressure.
  • Each line is connected with its own transducer 72 or 76, each with an output of 1 V per 1 00 mmHg (SenSym, output range of 1 to 1 5 volts with a base voltage of 1 volt at 0 mmHg).
  • Transducer 76 attached to air line 82, reads the air pressure coming into the girdle from the air compressor. When the onset of contraction is detected and meets the true contraction criteria, air passes through air line 80 until the internal girdle pressure reaches the target belt pressure established by the operator. When the girdle pressure reaches its target, air valve 72 switches off to block the air flow into the girdle.
  • transducer 76 detects the drop, and air valve 67 is activated to re-pressurize the girdle to target pressure.
  • valve 77 opens 30 seconds after initiation of the inflation process to deflate the girdle.
  • the microprocessor sets a minimum pressure increase of 1 0 mmHg for 5 seconds. Any rates below this are treated as tube kinking, triggering immediate deflation of the girdle and activating an audible alarm for 5 seconds or longer. If this safety device fails, an emergency stop button is provided. The emergency stop button opens valve 77 and closes valve 67 for emergency deflation.
  • the controller 1 Displaying various forms of outputs is an important function of the controller 1 .
  • the girdle pressure and the patient information are displayed on the screen.
  • numerous alert and alarm criteria may be optionally implemented within the device control software:
  • a normal contraction may last about 60 - 90 seconds.
  • abnormal contractions such as polysystole, skewed contractions and tachysystole may show a longer contraction period due to a slow return to a baseline. This may result in applying the high pressure onto the abdomen over an extended period.
  • the maximum duration at the target intrauterine pressure during the contraction will be established at 20 - 60 seconds. In the prototype, the limit was set at 30 seconds.
  • an average increase in maximum uterine pressure above basal level begins with about 20 - 30 mmHg at the early first stage of labor and becomes 40- 50 mmHg at the active phase and the second stage of labor.
  • This force is mainly produced by the primary and involuntary force.
  • the use of the inventive device will increase the intrauterine pressure further by providing the secondary force.
  • the target intrauterine pressures are assessed during various phases of labor.
  • the target intrauterine pressure during the stage of labor with cervical dilation from 3 cm to 8 cm is set at 40 - 60 mmHg above the baseline while during the active phase with cervical dilation from 8 cm to 1 0 cm at 60 - 80 mmHg and the second stage of labor at 80 - 1 60 mmHg.
  • the decision of ' whether the stage of labor is early or active should be made by a physician.
  • Obstetricians also set up the appropriate target intrauterine pressure depending on clinical situations. Any uncontrollable intrauterine pressure increase above the target pressure ( 1 5 mmHg higher than the target) will trigger the alarm system and rapidly deflate the girdle.
  • the limit of the girdle pressure will be set at 1 50 mmHg during the stage of labor with cervical dilation from 3 cm to 8 cm when the target intrauterine pressure is 40 - 60 mmHg.
  • the limit will be set at 250 mmHg during the active phase of labor with cervical dilation from 8 cm to 1 0 cm when the target intrauterine pressure is 60 - 80 mmHg.
  • the limit will be set at 350 mmHg during the second stage of labor.
  • the girdle pressure above these limits triggers the alarm system and rapidly deflates the girdle.
  • the girdle may also be implemented with its own safety valve which be blown if the pressure exceeds 350 mmHg.
  • a fault signal generated by non- contraction processes is filtered by setting a 5 second delay rule, i.e., a true contraction occurs if the intensity of the signal remains at 20% of full scale for 5 second.
  • the criteria for each of these situations is stored within a library in the controller's memory 40 and the contraction data is compared against these criteria to determine whether the abnormal condition is present. If so, an alarm condition is initiated and an output is provided to indicate the presence of the abnormal condition.
  • the following situations are included in the library of abnormal conditions:
  • hypocontractility When contractions are less than 25 to 30 mmHg at their peak, or recur less frequently than every five minutes in the active phase of labor and last less than 45 seconds, hypocontractility is present, even if it is accompanied by progress in labor.
  • the decreased uterine activity may be due to the abnormal contraction, hypotonia, or the artifact from the presence of air in the internal monitoring system. In both cases, the use of the device may not cause safety problems.
  • the alarm system will be on before the target intrauterine pressure is obtained.
  • the correction should be made upon a proper diagnosis of the above problems.
  • the presence of air in the internal monitoring system can be corrected easily and device can be restarted.
  • Polysystole is a common abnormal uterine waveform that is characterized by a single contraction with two or more peaks. It is also described as two or more contractions in juxtaposition without full return to the. baseline between each. This could be determined by software and if the situation meets the alarm criteria set in the above section, the girdle should deflate and a physician should be informed. 3. Discoordinate uterine activity:
  • the constancy of the intervals between uterine contractions determines the degree of coordination or rhythm of uterine activity.
  • the resultant pattern is termed "discoordinate labor" .
  • contractions may be generated from alternate uterine cornua as well as from other sites, frequent low intensity contractions are a typical finding. Since the controller sets up a threshold to evaluate the onset of contraction, some of the low-intensity contractions below this threshold may not trigger the girdle pressure to increase. This will be similar situation of hypotonia. In this case, the use of the device may not cause any safety problem.
  • Other discoordinate labor, Uterine hypertonus may result from the constantly contracting state of some area in the myometrium. Extreme degree of this phenomenon is uterine fibrillation. In this case, the use of the device should be avoided.
  • a skewed contraction is characterized by a prolongation of the descending limb (relaxation phase) of the uterine contraction and is often seen in a mixed pattern with polysystole.
  • the use of the inventive device implemented with a maximum duration at the target intrauterine pressure will not cause any problem.
  • Paired contractions are a form of increased uterine contraction frequently characterized by one uterine contraction in close temporal relationship to a second uterine contraction, with the waveform returning to baseline between the two contractions. Usually, the second contraction is smaller in amplitude. Since the device sets the minimum interval between two cycles of girdle pressure increase, its use under this condition will not cause any safety problem.
  • Tachysystole is defined as increased uterine contraction frequency. Because of the inevitable accompanying diminished or absent resting interval, decreased fetal oxygenation has been associated more often with this form of uterine hyperactivity than with increased intensity or duration of the uterine contraction. However, increased uterine activity of any type does not infer fetal stress or distress. Increased uterine activity may well be tolerated by some fetuses, whereas others may demonstrate stress even with uterine activity of a low intensity. As long as the fetus does not show distress, the use of the inventive device will not cause any problem. The software in device will diagnose the situation. However, a physician should make a final decision.
  • Tachysystole with progressive hypertonia Progressive hypertonia, usually associated with tachysystole, is a form of uterine dysfunction. It represents incomplete relaxation between frequently occurring contractions.
  • the software in the inventive device will diagnose the situation. However, a physician should make a final decision about continued use of the device.
  • Tachysystole with progression to tetany Progressive uterine hypertonus, characterized as a rising baseline tone, is often accompanied by tachysystole. During the relaxation phase, the uterine tone does not completely return to the prior resting phase level before the next contraction begins. This may progress to tetany.
  • the software in the inventive device will diagnose the situation. The use of the device should be decided by a physician under this circumstance.
  • the software in the labor assisting device will diagnose the situation.
  • the use of the device should be decided by a physician under this circumstance. 1 0.
  • Hypersystole The amplitude of intensity is the pressure difference (in mmHg) between the peak of the uterine contraction and the uterine tone preceding the contraction. Hypersystole is defined as greater than 60 mmHg maximum pressure. Contractions of greater than 60 mmHg are seen with pharmacologically overstimulated or spontaneous abnormal labor. If there is enough uterine pressure, the use of the device is not necessary. A physician will make a decision on continuing the use of the device.
  • the childbirth assisting device of the present invention effectively prevents prolonged duration of labor and dystocia due to systemic analgesia, epidural anesthesia, or maternal exhaustion, leading to reduction of the cesarean section rate and rate of instrumental delivery. Since weakening of the secondary labor force is particularly common in patients receiving epidural anesthesia, the device can effectively prevent weakening of the secondary labor force under anesthesia, enabling a safer and less painful delivery.
  • the inventive device includes means for analyzing the contraction curve and period in order to identify the presence of abnormal conditions, providing further safety benefits. Detection of intra-uterine pressure is enhanced by the use of a solid state pressure sensor, providing more accurate detection of contractions to facilitate synchronization of application of supplemental secondary force as well as to provide means for determining the presence of abnormal conditions.
  • Tocotransducer 1 60 is an embedded semiconductor pressure sensor which can be used or modified for use in other applications. Although the above description shows the pressure sensor pressed against the abdomen of a woman for monitoring contractions during labor, the pressure sensor can also be used for externally monitoring the pressure within other bodies which change shape in response to changing pressure.
  • the hardness of housing 1 66 can be modified to accurately measure the pressure within the body being measured based upon the results of analytical tests using different housing materials. Although the use of a pliable housing material which conforms to the patient's abdomen increases the accuracy of the contraction monitor described above, a stiffer or non-pliable material may provide suitable accuracy for other applications.

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Abstract

L'invention porte sur un capteur de pression à semi-conducteur noyé permettant de mesurer de l'extérieur une pression à l'intérieur du corps. Ledit capteur comporte un boîtier (166) flexible s'adaptant à peu près au corps lorsqu'il est pressé contre le corps, par exemple au moyen d'une ceinture traversant des fentes (168, 169) pratiquées dans le boîtier. Un bouton (172) saillant du boîtier transfert la force appliquée à sa surface extérieure quand le boîtier est pressé contre le corps, vers une cavité intérieure du boîtier jouxtant le bouton. Le capteur transistorisé reçoit la force transférée, la détecte et émet un signal électrique représentant la pression à l'intérieur du corps. Le capteur (180) transistorisé, enfermé dans le boîtier qui le protège de l'environnement, comporte un CI piézorésistant émettant un signal électrique de force quand il est déformé par la force à mesurer. Le CI est enchâssé dans un compartiment doté d'un piston (186) mobile transférant la force du bouton sur le CI. Un disque (187) de protection et un ressort (185) placés sur le piston mobile renforcent la protection du CI. Le capteur de pression peut par exemple servir à mesurer la pression intra-utérine en produisant des signaux indicatifs des contractions pendant le travail.
PCT/US1998/018070 1997-10-10 1998-08-31 Capteurs de pression a semi-conducteur noye, tocodynamometres WO1999019704A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU92972/98A AU9297298A (en) 1997-10-10 1998-08-31 Embedded semiconductor pressure sensors, tocodynamometers

Applications Claiming Priority (2)

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US94868097A 1997-10-10 1997-10-10
US08/948,680 1997-10-10

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Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1181890A1 (fr) * 2000-08-17 2002-02-27 GE Medical Systems Information Technologies, Inc. Détecteur d'un évènement physiologique, notamment pour la détection de contractions utérines
FR2816497A1 (fr) * 2000-11-10 2002-05-17 Plastiques Franc Des Dispositif de stockage et de distribution de sangles
WO2005051185A1 (fr) * 2003-11-25 2005-06-09 Pierfrancesco Belli Appareil automatique de suivi du travail d'accouchement
ES2322417A1 (es) * 2006-10-11 2009-06-19 Cleofas Rodriguez Blanco Sistema de dinamometria para tecnicas sanitarias manuales.
US7726197B2 (en) 2006-04-26 2010-06-01 Honeywell International Inc. Force sensor package and method of forming same
WO2012108950A1 (fr) 2011-02-08 2012-08-16 Board Of Trustees Of The University Of Arkansas Tocodynamomètre pneumatique
US8327715B2 (en) 2009-07-02 2012-12-11 Honeywell International Inc. Force sensor apparatus
US8806964B2 (en) 2012-03-23 2014-08-19 Honeywell International Inc. Force sensor
US9003897B2 (en) 2012-05-10 2015-04-14 Honeywell International Inc. Temperature compensated force sensor
US9003899B2 (en) 2012-03-23 2015-04-14 Honeywell International Inc. Force sensor
EP3062684A1 (fr) * 2013-10-30 2016-09-07 NociTech ApS Système d'évaluation de la modulation de la douleur, de la totalisation spatiale et/ou temporelle de la douleur ou de l'inhibition décroissante de la douleur chez un humain
CN109561839A (zh) * 2016-08-09 2019-04-02 皇家飞利浦有限公司 母体监测换能器和操作方法
CN109805900A (zh) * 2019-04-01 2019-05-28 清华大学 宫缩压力柔性检测设备

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US3913563A (en) * 1974-03-08 1975-10-21 Medical Instr & Technology Contraction monitor
US5218972A (en) * 1988-04-29 1993-06-15 Healthdyne, Inc. Biomedical force measuring apparatus
US5645563A (en) * 1993-06-30 1997-07-08 Novatrix, Inc. Child-birth assisting system

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Publication number Priority date Publication date Assignee Title
US3913563A (en) * 1974-03-08 1975-10-21 Medical Instr & Technology Contraction monitor
US5218972A (en) * 1988-04-29 1993-06-15 Healthdyne, Inc. Biomedical force measuring apparatus
US5645563A (en) * 1993-06-30 1997-07-08 Novatrix, Inc. Child-birth assisting system

Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1181890A1 (fr) * 2000-08-17 2002-02-27 GE Medical Systems Information Technologies, Inc. Détecteur d'un évènement physiologique, notamment pour la détection de contractions utérines
US6547748B1 (en) 2000-08-17 2003-04-15 Ge Medical Systems Information Technologies, Inc. Physiological event detector and method of operating the same
FR2816497A1 (fr) * 2000-11-10 2002-05-17 Plastiques Franc Des Dispositif de stockage et de distribution de sangles
WO2005051185A1 (fr) * 2003-11-25 2005-06-09 Pierfrancesco Belli Appareil automatique de suivi du travail d'accouchement
US7144379B2 (en) 2003-11-25 2006-12-05 Pierfrancesco Belli Automatic apparatus for controlling the childbirth labor
US7726197B2 (en) 2006-04-26 2010-06-01 Honeywell International Inc. Force sensor package and method of forming same
ES2322417A1 (es) * 2006-10-11 2009-06-19 Cleofas Rodriguez Blanco Sistema de dinamometria para tecnicas sanitarias manuales.
US8327715B2 (en) 2009-07-02 2012-12-11 Honeywell International Inc. Force sensor apparatus
WO2012108950A1 (fr) 2011-02-08 2012-08-16 Board Of Trustees Of The University Of Arkansas Tocodynamomètre pneumatique
EP2672891A1 (fr) * 2011-02-08 2013-12-18 Board of Trustees of the University of Arkansas Tocodynamomètre pneumatique
EP2672891A4 (fr) * 2011-02-08 2014-09-24 Univ Arkansas Tocodynamomètre pneumatique
EP3017762A1 (fr) * 2011-02-08 2016-05-11 Board of Trustees of the University of Arkansas Tocodynamomètre pneumatique
US8806964B2 (en) 2012-03-23 2014-08-19 Honeywell International Inc. Force sensor
US9003899B2 (en) 2012-03-23 2015-04-14 Honeywell International Inc. Force sensor
US9003897B2 (en) 2012-05-10 2015-04-14 Honeywell International Inc. Temperature compensated force sensor
EP3062684A1 (fr) * 2013-10-30 2016-09-07 NociTech ApS Système d'évaluation de la modulation de la douleur, de la totalisation spatiale et/ou temporelle de la douleur ou de l'inhibition décroissante de la douleur chez un humain
CN109561839A (zh) * 2016-08-09 2019-04-02 皇家飞利浦有限公司 母体监测换能器和操作方法
CN109561839B (zh) * 2016-08-09 2022-12-06 皇家飞利浦有限公司 母体监测换能器和操作方法
CN109805900A (zh) * 2019-04-01 2019-05-28 清华大学 宫缩压力柔性检测设备

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