WO2007130958A2

WO2007130958A2 - Passive phonography heart monitor

Info

Publication number: WO2007130958A2
Application number: PCT/US2007/067906
Authority: WO
Inventors: Ezra J. Rapoport; Nicholas P. Orenstein
Original assignee: Lono Medical Systems, Llc
Priority date: 2006-05-02
Filing date: 2007-05-01
Publication date: 2007-11-15
Also published as: AU2007248156A1; EP2019618A2; CA2650959A1; WO2007130958A3; IL195047A0; EP2019618A4; AU2007248156B2

Abstract

A fetal heart monitor device (12) includes a channel to receive a first signal representative of acoustic energy principally from a maternal heartbeat (18a) and a second signal representative of acoustic energy including a fetal heart beat (18c). The device includes a computing device including a processor, a memory operatively coupled to the processor, and non-volatile storage operatively coupled to the processor, the non-volatile storage storing a computer program including instructions to cause the processor to process the first and second electrical signals into an electrical signal representative of the acoustic energy emitted by the fetal heart.

Description

PASSIVE PHONOGRAPHY HEART MONITOR

BACKGROUND

This invention relates to medical monitoring, and m particular fetal heart monitoring.

Fetal heart monitoring 1$ a diagnostic tool to indicate the overall heulth status of a fetus. Currently deployed fetal heart monitoring techniques are primarily ultrasound, Doppler-based. With a typical ultrasound Doppler-based technique, wires are deployed between an ultra sound transducer unit and processing unit, A skilled operator, such as a medical technician or nurse scans or places a transceiver on the abdomen of the patient. Typically, the operator covers a region on the abdomen with a gel and moves the ultrasonic sensor around the area to scan the area. Alternatively, the sensor can be affixed with a belt- that is worn around the woman. The belt is cumbersome and inaccurate (often the sensor slips off of its target) and .it has to be removed prior to any surgery or emergency procedure. Acoustic signals are emitted from the transducers and their echo signals are delected by the transceiver and processed to produce data pertaining to the fetal heart rate.

Current Dαppier-based techniques for fetal monitoring have several limitations. One limitation of current Doppler-based techniques is the lack of speeiikitv for detecting fetal heart tones (Fi-FPx). In cases of maternal tachycardia, the operator may not be able to differentiate whether the transducer is det.eeti.ng the fetal or maternal signal , and this cars have catastrophic consequences.

Other limitations pertain to changes in fetal position or station which otten require re-positioning of the transducer, which can be time-consuming and result in "blackout" periods in fetal monitoring, during which medical personnel do not receive data from monitors thai monitor the fetus, Another limitation is the loss of continuous monitoring m a distressed fetus, especially during transition periods, e.g., moving from a delivery room to an operating room tor an emergency Cesarean section procedure. In addition, many hospital protocols require detachment of all wires from fetal monitoring devices during room transfers. Detaching fetal monitors begins another "blackout period.⁵'

Administration of epidural anesthesia presents another potential "blackout" period for fetal monitoring, as the transducer is frequently removed or displaced during that procedure. This, too, is a critical time frame for fetal monitoring, as epidural anesthesia may cause maternal hypotension with subsequent fetal bradycardia. Maternal ambulation has been shown to facilitate labor progress,, but current techniques typically preclude such standing deliveries.

A newer monitoring technique known as fetal phonography uses a passive acoustic sensor to capture- acoustic energy from the maternal abdomen. Typically, the sensor includes a piezoelectric element, ϊn a paper entitled "Development of a Piezopoiymβr Pressure Sensor for a Portable Fetal Heart Rate Monitor" by Allan J. Zuckerwar et aJL, IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING VOL. 40, NO. 9. SEPTEMBER 1993 p. 963, the authors described a pressure sensor array mounted on a belt worn by the mother. The sensor array uses two polyviπyldene fluoride elements arranged in a birnorph structure, mechanically in series and electrically in parallel

SUMMARY

According to an aspect of the present invention, a fetal heart monitor device Includes a channel to receive a first signal representative of acoustic energy principally from a maternal heartbeat and a second signal representative of acoustic energy Including a fetal heart beat. The device includes a computing device including a processor, a. memory operative!}' coupled to the processor and non-volatile storage operative!}' coupled to the processor, the aim-volatile storage storing a computer program including instructions to cause the processor to process the first and second electrical signals into an electrical signal representing acoustic energy principally of the fetal heartbeat.

The following are embodiments within the scope of the claims. The device includes a channel to receive a third signal representative of acoustic energy of uterine contractions and the program includes instructions to process the third electrical signal into a.α indication of maternal uterine rates of contraction, The device includes instructions to process the second electrical signal to provide an electrical signal representative of acoustic energy principally of the maternal heartbeat. The device includes instructions to render the electrical signal representative of the Fetal heartbeat on an output device. The device includes an audio speaker and the electrical signal is rendered by the speaker to produce an audio representation of the fetal heartbeat. The device Includes a display and the electrical signal is rendered by the display $o produce representation of the fetal heartbeat. The device includes a display and the electrical signal is rendered by the display to provide a representation of the fetal heartbeat rate. The device includes a pair of acoustic transducers each comprising a polymer that exhibits piezoelectric properties, and which converts acoustic energy into the first and second signals, The device includes three acoustic transducers each comprising a polymer that exhibits piezoelectric properties, and which converts acoustic energy into the first, second and third signals. The device includes a pair of acoustic transducers each comprising a polymer that exhibits piezoelectric properties, which converts acoustic energy into the first and second signals and a strain gauge that provides a third signal representative of maternal contractions. The pair of transducers are coupled to the monitor, via wires or cables to provide the first and second signals to the channel.

Each of the first and second transducers includes circuitry to wireless Iy transmit data over the first and second channels to the monitor and the monitor includes circuitry to receive the wirelessiy transmitted data. The circuitry to wireiessly transmit data includes radio frequency transmitter circuitry. The circuitry to wirelessiy transmit data includes circuitry to transmit a unique transducer identification code to the monitor. Each transducer includes a polymer sheet of poiyvinvidene fluoride and/or co- polymers thereof.

According to a further aspect of the present Invention, a method of monitoring fetal heart beat includes receiving over a -first channel, a first signal representative of acoustic energy principally from a maternal heartbeat, receiving, over a second channel, a second signal representative of acoustic energy including a fetal heart, beat and processing the first and second electrical signals into an electrical signal representing acoustic energy principally of the fetal heartbeat.

The following are embodiments within the scope of the invention.

The method includes converting acoustic energy representative of maternal uterine contractions into a third electrical signal. The method includes processing the first and second electrical signals to provide the electrical signal representative of acoustic energy principally due to the fetal heartbeat, the second signal to provide a signal representative of the maternal heart and the third signal to provide a signal representative of maternal uterine contractions. The method includes rendering the electrical signals representative of the fetal heartbeat, maternal heartbeat and uterine contractions on an output device. 'The method includes applying principal component analysis to digital representations of the signals. The method includes wirekssjy transmitting data from a pair of transducers disposed on the patient over the first and second channels to provide the first and second signals. According to a further aspect of the present invention, a fetal bear!, monitor device includes a channel to receive a first signal representative of acoustic energy principally itcmi s maternal heartbeat and a second signal representative of acoustic energy including a fetal heart beat and circuitry to process the first and second electrical signals into an electrical signal representing acoustic energy principally of the fetal heartbeat.

The following are embodiments within the scope of the invention.

The device includes a channel to receive a third signal representative of acoustic energy of uterine contractions and circuitry to process the third electrical signal into an indication of maternal uterine rates of contraction. The device includes circuitry to render the electrical signal representative of the fetal heartbeat on an output device. The device includes circuitry to modulate the fetal heart tone into the audible frequency range and an audio speaker to render art audio representation of the fetal heartbeat. The device includes a display to render a visual representation of the fetal heartbeat. The device includes a display to render a value indicative of fetal heartbeat rate.

One or more aspects of the invention may provide one or more of the following advantages.

The monitor is capable of functioning without a skilled technician being present. Additionally, the monitor can be relatively low in cost compared to currently employed ultrasound based monitors by avoiding need for relatively expensive crystals commonly employed in the ultrasound transducers. The monitor uses low-cost sensing, transmission, and circuitry components suitable for operation in hospitals, physician offices, or home.

The monitor uses transducer sensor units that are disposable. The disposable nature of the transducer sensor units enables the monitor to ensure a very high standard of accuracy for these transducer sensor units because the term of use for each transducer sensor uπil will not exceed a specified time duration. Hence, normal concerns of quality degradation resulting from extended use are avoided, while maintaining a relatively high level of performance. The monitor avoids blackout periods, e.g., the potentially most dangerous window of time during labor since the monitor in the wired and especially the wireless form allows for constant .monitoring. Accurate, wireless monitoring system aids in decreasing labor time by increasing the potential mobility of the patient, thus making the resources in a labor-and -delivery unit more available.

The monitor uses a pitch period detector, a principal component analyzer and a complex wavelet transform analysis technique to analyze signals from the sensors. This pennies sophisticated and accurate fetal signal processing to be employed in the monitor at a relatively low cost, The monitor allows for maternal ambulation during labor, providing a number of potential benefits.

According to an additional aspect of the present invention, an acoustic transducer includes a base member, a polymer sheet having a pair of electrodes disposed over major, opposing surfaces of the polymer sheet, the polymer sheet disposal adjacent an exterior portion of the base member, a cap affixed to the base member and electrical circuitry carried by the acoustic transducer and coupled to the electrodes on the polymer sheet,

The following arc embodiments with the scope of the invention. The circuitry is disposed between the base and the cap. The cap has a convex surface. The cap and the base member arc secured together. The base has an aperture and the polymer sheet is supported in the aperture isi the base b> attaching a securing member to one of the major surfaces of the polymer, the one major surface being on an externa! surface of the acoustic transducer.

An exterior surface of the base member has an adhesive layer ihereori to adhere the transducer to epidermis of a subject. The exterior surface of the base member has an adhesive layer thereon to support an outer one of the major surfaces of the polymer mid to adhere the transducer to epidermis of & subject. The adhesive layer provides an acoustic impedance coupling between the outer one of the major surfaces of the polymer and epidermis of the subject. The adhesive layer is a doubie-sidcd tape.

The circuitry comprises a transmitting device to wirelessiy transmit signals from the transducer. The circuitry includes a low noise, high impedance amplifier coupled to receive a voltage potential produced across electrodes of the polymer sheet and a transmitting device coupled ?o the output of the amplifier to wirelessiy transmit an output signal from the transducer. The circuitry comprises circuitry to couple wires or cables to output signals iτom the transducer. The circuitry includes a low noise, high impedance amplifier coupled to receive a voltage potential produced across electrodes of the polymer sheet and & connector to couple signals from the amplifier to the wires or cables. The aperture in the base rnoraber is a generally rectangular aperture in a substantial portion of the base member.

The aperture in the base member is a generally Y- shaped aperture having three regions, the aperture hi a substantial portion of the base member and the acoustic transducer includes an additional pair of polymer sheets, with the polymer sheet and the addition pair of polymer sheets disposed in the three regions of the aperture, The bast; member and cover are secured together by a plurality of snap latches on one of the cover and base that mate with receptacles on. the other one of the cover and base to secure the base to the cover. The transducer body is a round shape. The transducer is for heart, monitoring. The the polymer sheet is polyvinyldene fluoride and/or a co-polymer thereof. The base and cover are comprised of a relative!)' strong plastic material that is sufficient in strength to support the weight of a pregnant woman. The the base imά cover are comprised oi^'an ABS plastic any of a class of plastics based on aerylonitrile-butadiene-styrene copolymers. The base has an aperture and the polymer member is disposed within the aperture of the base. The base has an aperture lilted with an acoustic foam materials and the polymer member is disposed within the aperture of the base. The polymer member is disposed against the exterior portion of the base.

According to a further aspect of the present invention, an acoustic transducer includes a base member having an. aperture and a polymer sheet comprised of poiyvuiykiene fluoride and/or a co-polymer thereof, the sheet having a pair of electrodes disposed over major, opposing surfaces of the sheet, with the sheet, disposed in the aperture in the base member. The transducer also includes a cap affixed to the base member and electrical circuitry disposed in the acoustic transducer and electrically coupled to the electrodes on the sheet.

The following axe embodiments with in the scope of the invention. The circuitry includes a transmitter to transmit signals from the polymer sheet. The circuitry includes a low nøsse, high impedance amplifier coupled to receive a voltage potential produced across electrodes of the sheet and a transmitting device coupled to tlic amplifier to wireiessiy transmit an output signal from the amplifier. The cap has a convex surface. The sheet is supported in the aperture by attaching an adhesive to one of the major surfaces of the polymer, the one major surface being on an external surface of the acoustic transducer. The adhesive layer adheres the transducer to epidermis of a subject. The adhesive layer provides an acoustic impedance coupling between the outer one of the major surfaces of the polymer and epidermis of the subject, The adhesive layer is a double-sided tape. The circuitry includes circuitry to couple wires or cables to output signals from the transducer. The circuitry includes a low noise, high impedance amplifier coupled to receive a voltage potential produced across electrodes of the sheet and a connector to couple signals from the amplifier to the wires or cables. The aperture in the base member is a generally rectangular aperture in a substantial portion of the base member. The aperture in lhe base member is a generally Y-shaped aperture having three regions, the aperture in a substantial portion of the base member and wherein the acoustic transducer Includes an addiiionai pair of polymer sheets, with the polymer sheet and the addition pair of polymer sheets disposed in the three regions of the aperture. The transducer is for heart monitoring. The base and cover arc comprised of a relatively strong plastic material that is sufficient in strength to support the weight of a pregnant woman. The base and cover are comprised of OR ABS plastic any of a class of plastics based on acrylonUrile-butadiene-styrene copolymers. The base has an aperture tilled with an acoustic foam materials and the sheet is disposed within the aperture of the base.

One or more aspects of the invention may provide one or more of the IbI lowing advantages.

The transducers are affixed to the patient, which avoids the need for a skilled technician to b« present while a monitor attached to the transducers is operating. The transducers can be relatively low cost due to the use of the polymer ay compared to more expensive crystals used in Doppler techniques used with ultrasonic transducers. The transducers use low-cost sensing, transmission, and circuitry components suitable for operation in hospitals, physician offices, or home. The transducers are disposable. The disposable nature of the transducers enables the monitor to ensure a very high standard of accuracy for these transducer sensor units because the term of use for each transducer sensor unit will not exceed a specified time duration. Hence, normal concerns of quality degradation resulting from extended use are avoided, while maintaining a relatively high level of performance. The wireless versions of the transducer when employed with a monitor can avoid blackout periods, e.g., the potentially most dangerous window of time during labor since the wireless form allows for constant monitoring. Accurate, wireless monitoπng system aids in decreasing labor time by increasing the potential mobility of the patient, thus making the resources in a labor-and-dclivεry unit more available.

According to a further aspect of the present invention, a method includes converting acoustic energy representative principally of a maternal heartbeat into a first electrical signal, converting acoustic energy representative of a maternal heartbeat and a fetal heartbeat into a second electrical signal and processing the first and second electrical to provide an electrical signal principally representative of the fetal heartbeat. ^'Hie method further includes determining pitch periods of the signal principally representative of the fetal heart beat. The follow embodiments are within the scope of the invention. The method further includes converting acoustic energy representative of maternal uterine contractions into a third electrical signal. The method further includes rendering the electrical signal principally representative of the fetal heartbeat on an output device. The method further includes determining principal components of determined pitch periods of the signal principally representative of the fetal heartbeat. The method further includes modulating the electrical signal principally representative of the fetal heartbeat with a signal in the audible spectrum of human hearing.

The method further includes determining an initial period length value of the signs] principally representative of the fetal heartbeat by finding a eepsirum of the first, lew pitch periods of the signal principally representative of the fetal heartbeat to determine the frequency of the signal. The method further includes determining a beginning and ending point of each pilch period in the signal principally representative of the fetal heartbeat. The method further includes determining a variation of time durations between pilch periods and using the length of a prior period as an input to determine the duration of a subsequent pitch period. The further includes applying principal component analysis to the determined pitch periods to compress data representing the determined pitch periods. The method further includes processing the determined pitch periods to provide a representation, compressing the representation of the determined pitch periods, and storing the compressed representation of the determined pitch periods.

According to a further aspect of the present invention, a computer program product residing on a computer readable medium for detecting fetal heartbeat energy includes instructions to convert acoustic energy representative principally of a maternal heartbeat into a first electrical signal, convert acoustic energy representative of a maternal heartbeat and a fetal heartbeat into a second electrical signal, process the first and second electrical to provide an electrical signal principally representative of the fetal heartbeat and determine pitch periods of the signal principally representative of the fetal heart beat.

The following are embodiments within the scope of the invention.

The computer program product further includes instructions to convert acoustic energy representative of maternal uterine contractions into a third electrical signal. The computer program product timber includes instructions to render the electrical signal principally representative of the fetal heartbeat on an output device. The computer program product further includes instructions to determine principal components of determined pitch periods of the signal principally representative of the fetal heartbeat. The computer program product farther includes instructions to modulate the electrical signal principally- representative of the fetal heartbeat with a signal m the audible spectrum of human hearing.

The computer program product further includes instructions to determine an initial period length value of the signal principally representative of the fetal heartbeat by finding a eepstrum of the fkst few pitch periods of the signal principally representative of the fetal heartbeat to determine the frequency of the signal. The computer program product further includes instructions to determine a beginning and ending point of each pitch period in the signal principally representative of the fetal heartbeat. The computer program product further includes instructions Io determine a variation of time durations between pitch periods and use the length of a prior period as an input to determine the duration of a subsequent pitch period. The computer program product further includes instructions to apply principal component analysis to the determined pitch periods to compress data representing the determined pitch periods. The computer program product further includes instructions to process the determined pitch periods to provide a representation, compress the representation of the determined pitch periods and store the compressed representation of the determined pilch periods.

According to an additional aspect of the present invention, an apparatus includes circuitry to convert acoustic energy representative principaHy of a maiema! heartbeat into a first electrical signal, circuitry to convert acoustic energy representative of a maternal heartbeat and a fetal heartbeat into a second electrical signal, circuitry to process the first and second electrical to provide an electrical signal principally representative of the fetal heartbeat and circuitry to determine pitch periods of the signal principally representative of the fetal heart beat

The following are embodiments within the scope of the invention,

The apparatus includes circuitry to convert acoustic energy representative of maternal uterine contractions into a third, electrical signal. The apparatus includes circuitry to render the electrical signal principally representative of the fetal heartbeat on an output device. The apparatus includes circuitry to determine principal components of determined pitch periods of the signal principally representative of the fetal heartbeat. The apparatus includes circuitry to modulate the electrical signal principally representative of the fetal heartbeat with a signal in the audible spectrum of human hearing. The apparatus includes circuitry to determine an initial period length value of the signal principally representative of the fetal heartbeat by finding a cepstrum of the first few pitch periods of the signal principally representative of the fetal heartbeat to determine the frequency of the signal

The apparatus includes circuitry to determine a beginning and ending point of each pitch period in the signal principally representative of the fetal heartbeat. The apparatus includes circuitry to determine a variation of time durations between pitch periods and circuitry to use the length of a prior period as an input to determine the duration of a subsequent pitch period. The apparatus includes circuitry to apply principal component analysis to the determined pitch periods to compress data representing the determined pitch periods. The apparatus includes circuitry to process the determined pitch periods to provide a representation, compress the representation of the determined pitch periods, and store the compressed representation of the determined pitch periods.

The monitor is capable of functioning without a skilled technician being present. Additionally, the monitor can be relatively low in cost compared to currently employed ultrasound based monitors by avoiding mod for relatively expensive crystals commonly employed in the ultrasound transducers. The monitor uses low-cost sensing, transmission, and circuitry components suitable for operation in hospitals, physician offices, or home environments.

The monitor uses transducer sensor units thai are disposable. The disposable nature of the transducer sensor units enables the monitor to ensure a very high standard of accuracy for these transducer sensor units because the term of use for each transducer sensor unit will not exceed a specified time duration. Hence, normal concerns of quality degradation resulting from extended use are avoided, while maintaining a relatively high level of performance. The monitor avoids blackout periods, e.g., the potentially most dangerous window of time during labor since the monitor in the wired and especially the wireless form allows for constant monitoring. Accurate, wireless monitoring system aids in decreasing labor time by increasing the potential mobility of the patient, thus making the resources in a iabor-and-delivery unit more available.

The monitor uses a pitch period detector, a principal component analyzer, and a complex wavelet filter bank to analyze signals from the sensors. This permits sophisticated and accurate fetal signal processing to be employed m the monitor at a relatively low cost. The monitor allows for maternal ambulation during labor, providing a number of potential benefits.

According to an aspect of the present invention, a .method of acoustic monitoring includes transducing acoustic energy from a first acoustic transducer attached to a first location on a patient the acoustic energy from the first transducer, comprising desired acoustic energy to be monitored and interfering acoustic, energy, transducing acoustic energy from a second acoustic transducer, attached to a second, different location on a patient, the acoustic energy from the second transducer, comprising desired acoustic energy to be monitored and interfering acoustic energy, converting the acoustic energy sensed si the first and second locations Into first and second eleetxical signals and processing the first and second electrical signals to digitally remove interfering acoustic energy present in the second signal to provide an electrical signal representative of the acoustic signal that is being monitored.

The following are embodiments within the scope of the invention.

The interfering acoustic energy is principally representative of a maternal heartbeat The acoustic energy to be monitored includes acoustic energy representative of a fetal heartbeat and processing the first and second electrical signals provides the electrical signal representative of the fetal heartbeat. The method includes transducing a plurality of signals from a plurality of transducers, including the first transducer, the plurality of signals representing the acoustic energy to be monitored and processing the first the plurality of signals along with the second electrical signal to provide the electrical signal representative of the acoustic energy to be monitored. The acoustic energy to be monitored includes acoustic energy representative of a fetal heartbeat and processing the plurality of signals including the first signal, and second electrical signals provides the electrical signal representative of the fetal heartbeat.

According to an aspect of the present invention, a method of monitoring health status of a terns includes transducing acoustic energy from a first acoustic transducer attached to the epidermis about the vicinity of the abdomen of a pregnant woman, the acoustic energy from the first transducer, comprising acoustic energy of a fetal heartbeat and interfering acoustic energy of a maternal heartbeat, transducing acoustic energy from a second acoustic transducer, attached to the pereordium region of a pregnant woman, the acoustic energy from the first transducer the acoustic energy from the second transducer, comprising the interfering acoustic energy of the maternal heartbeat, converting the acoustic

U energy sensed at the first and second locations into first and second electrical signals and processing the first and second electrical signals to provide an output signal representative of the fetal heartbeat

The interfering acoustic energy is removed during processing of the first and second signals. The processing includes processing at least the second electrical signal to provide a second output signal representative of the maternal heartbeat. The second transducer is attached beneath the pereordium area of the patient. The method includes converting acoustic energy representative of maternal uterine contractions into a third electrics] signal The method includes processing the third electrical signal to provide a signal representative of a rate of maternal uterine contractions. The method is applied to monitor fetal heartbeats and includes attaching the first transducer to the abdominal region of the patient in a region where the back of the fetus is against the maternal abdominal wail.

The method includes rendering the electrical signal representative of the fetal heartbeat on an. output device. The output device is an audio speaker, 'live output device is a display device that renders an electrocardiogram. The output device is a display device that renders readout of heartbeat rate. The method includes rendering the second output signal representative of the maternal heartbeat on an output device. Hie acoustic transducers are wireless. The acoustic transducers are coupled to a processing device via cables and/or wires.

The monitor is capable of functioning without a skilled technician being present. Additionally; the monitor can be relatively low in cost compared to currently employed ultrasound based monitors by avoiding need for relatively expensive crystals commonly employed in the ultrasound transducers. The monitor uses low-cost, sensing, transmission, and circuitry components suitable for operation in hospitals, physician offices, or home.

The monitor uses transducer sensor units that are disposable. The disposable nature of the transducer sensor units enables the monitor to ensure a very high standard of accuracy for these transduce? sensor units because the term of use for each transducer sensor unit will not exceed a specified time duration. Hence, normal concerns of quality degradation resulting from extended use are avoided, while maintaining a relatively high level of performance. The monitor avoids blackout periods, e.g., the potentially most dangerous window of time during labor since the monitor in the wired and especially the wireless form allows for constant monitoring. Accurate, wireless monitoring system aids ϊn decreasing labor lime by increasing the potential mobility of the patient, thus making the resources in a labor-and-ddivcry unit more available.

The monitor uses a pitch period detector and a principal component analyzer to analyze signals from the sensors. This permits sophisticated and accurate fetal signal processing to be employed in the monitor at a relatively low cost. The monitor allows for maternal ambulation during labor, providing a number of potential benefits.

The details of one or more embodiments of the invention are set forth in the accompanying drawings ami the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

HG 1 is a block diagram of a monitoring scheme.

FIG 2 is a block diagram of fetal monitor device used to monitor fetal cardiac activity.

FiCr. 3 is a flow chart depicting aspects of processing in the fetal monitoring device of FIG 2.

FIG 4 is a block diagram of an alternative fetal monitor device,

FIG 5 is a block diagram depicting processing,

FIGS. 6A-6E-8A-SC (collectively, FiGS, 6-8) are diagrams depicting construction details of sensors used with the monitor of FIG 3.

FIGS. 9A-9B (collectively FIG 9) is a set of diagrams depicting an alternate pattern for a piezoelectric sensor element.

FIG 10 is a block diagram of circuitry used in the sensors.

FIG 1 .1 is a schematic of a high impedance amplifier used with the sensors of PiGS. 6-8,

FIG 12 is a block diagram depicting details of pitch processing

FlG, 13 is a flow chart depicting pitch processing,

FIGS. 14A and 14B are diagrams useful in understanding processing of fetal and maternal heartbeat signals.

FiG 15 is a flow chart depicting principal component analysis. DETAILED DgSCRirπOft

Referring to FIG. 3, an arrangement 10 for connection of a monitor device 12 ("monitor") to a patient, e.g., pregnant woman 14 to monitor fetal heartbeat signals is shown. The monitor 12 can be used for various types of monitoring, as discussed below, to this example, the monitor 1.2 is a fetal heartbeat monitor.

The monitor 32 (discussed in detail below) has acoustic transducer (sensors) 16a- KSc that convert acoustic energy from the pregnant woman 14 into electrical energy. The transducers 16a- 16c are coupled to the monitor 12, via communication channels, ISa-ISc, which can be wires connecting to the monitor Yl or wireless channels (radio frequency, optical and/or infrared). In one embodiment, Bluetooth® wireless technology is used.

In one configuration for connection of the monitor 12 to the patient, one of the transducers, e.g., transducer 16a monitors the pregnant woman's heartbeat, another one of the transducers 16b monitors the pregnant woman's uterus to measure uterine contractions. The transducer to monitor the uterine contractions, is not essential to capturing the fetal heartbeat but is included as part of an overall tool to monitor the health arid status of the patient and fetus. The third transducer lόc monitors the fetal heartbeat. The location of the pregnant woman's heart and uterus are readily predictable. The acoustic energy from the fetal heart is omnϊ-dirεctional but localized about the back of the fetus. Such localization .Ls attributed to preferred acoustic propagation to sites where the fetal back is against the maternal abdominal wall The acoustic propagation through the maternal wall is omnidirectional but there is a point of maximum acoustic conduction, which is the point where the fetus' back is pressed against the uterine wall. However, other positions can he used to attach the transducer 16c to the pregnant woman. hi another configuration for connection of the monitor 12 to the patient, transducer 16a is arranged to monitor the pregnant woman's heartbeat and transducers 16b monitors the pregnant woman's uterus to measure uterine contractions. To capture fetal acoustic energy, a plurality of transducers (.not shown) 16c can be deployed to monitor the fetal heartbeat. The multiple acoustic transducer 16c are deployed for fetal detection and arranged about the maxima^] fetal acoustic energy. This is a noise reduction technique that can be used hi cases where it is difficult to sense the fetal heartbeat (e.g., i.n the case of an overweight pregnant woman or underweight fetus) extra fetal sensors can he deployed to boost the strength of the fetal signal. Furthermore, 3 or more fetal sensors can be used to

U triangulate the position of the fetal heart. This localization information can be used by doctors and technicians during labor and delivery.

Referring to FlG. 2, the monitor 12 includes a processor 30, e.g., a general purpose centra! processing unit (CPU) and/or a digital signal processor (DSP) to process signals fwm the patient, a memory 32, to execute programs, persistent, e.g., mm- volatile storage 34, and I/O interfaee(s) 36 all coupled via a bits 38. Executed by the monitor 12 is signal processing software 50 that processes ECG signals detected by transducers 14a and 14c from the pregnant woman's heart and the fetus's heart, respectively. The monitor } 2 also processes signals from the transducer 14b that monitors for contractions In the pregnant woman's uterus.

Processing 50 provides a relatively clean detection of the fetal heartbeat by eliminating major sources of noise in the fetal heartbeat signal, e.g., the relatively strong acoustic energy components contributed to the detected fetal heartbeat caused by the pregnant woman's heartbeat, hi some embodiments, acoustic energy components from uterine contractions could also be filtered from the detected fetal heartbeat acoustic energy, but in general that is an insignificant contributor to noise in detection of the fetal heartbeat

The monitor 10 can also include other user interface devices, e.g., keyboard or keypad, a display, speakers, headphone, etc. (not shown). In addition, the monitor can include a transmission channel to upload data to a server or the like.

Referring to FiG. 3, the monitor 12 includes an interface 36 thai interfaces the monitor 12 to the transducers 16a- 16c, The interface 36 here is shown to include channels 36a-36e for transducers 16a-lόe, respectively. Each channel 36a-36e includes a receiver 40 (if the monitor is a wireless version) or an analog signal interface (not shown) to cables (not shown) from the transducer, if the monitor 12 is a wire-connected version, Sn addition, the interface 36 includes a low noise amplifier and a filter generally 42 to process analog signals from the transducers 16a- 16c.

The amplifier 14 amplifies the signals and the filter filters the signals to preserve frequencies hi the range of, e.g., 0.05 to 100 Hz or so. Typically, the fetal channel in the monitor 12 can be within, the broad range above, but most likely will in a range about 10 to 30 Hz and especially in a range of 18 to 25 Hz (the range of maxima! spectral power of the fetal heart signal). The maternal channel can be within the broad range above, but most likely will hi a range about 6 to 14 Hx and especially hi a range of S to 12 Hz (the region of maximal power of the maternal heart signal). Whereas, the transducer !4b thai senses the maternal contractions need not have any filtering since it is a very long period, e.g., a large impulse.

Each amplifier 14 feeds the signal to an AJD converter 44 that digitizes the signal, at a sampling frequency at least greater than twice the highest frequency component in the channel. In oilier implementations, a single A/D converter arid a multiplexer can be used to process data from the channels (See FIG. 4). The digitized signals from each of the channels are transferred to the bus interface device 46 that formats the digitized signals to place on the bus 3 S (FΪG. 2.) to send to the memory 34 and/or processor 32 to be processed.

Referring to FiG. 4, an alternative arrangemeat for the monitor 12 interfaces the monitor 12 to the transducers 1 Oa-16c. A channel 36a-36e is provided for each transducer 16a-l 6c. Each channel 36a-36c includes a receiver 40 (if the monitor is a wireless version) or ail analog signal interface (not shown) to cables (not shown) from the transducer, if the monitor is a wire-connected version. In addition, the interlaces 36a to 36c include a low noise amplifier and a filter generally 42 to process analog signals from the transducers 16a and 16c and a low noise amplifier generally 42' to process analog signals from the transducer 16b.

The amplifier 14 amplifies the signals and the filter filters the signals to preserve frequencies in the ranges discussed above. Each amplifier/filter 42 and ampHfrer 42' selectively feeds its output signal to a A/D converter/multiplexer 44 that digitizes the signal at a sampling frequency at least greater than twice the highest frequency component in the channel according to control provided from the processor. The single A/D converter and multiplexer 44 processes data in the selected channel and transfers the data to the digital signal processor 45 (DSP) for processing described below.

A processor 48 processes signals from a front panel to control the ADC/mux 44, whereas the DSP 45 processes output signals from the ADO'mux 44 to provide outputs to the front panel In some implementations this can be the same device. The front panel thus includes a display, a digital readout, switches (to select which channel to process), speakers, and so forth- The monitor 10 can also include other user interface devices, e.g., keyboard or keypad, and interfaces for connection to other equipment to upload data to a server and the like.

The arrangement also includes .memory, to execute programs, persistent, e.g., nonvolatile storage, and I/O interfaces) all coupled via buses (not shown] to the digital signal processor 45 and processor 48, Executed by DSP 45 is signal processing software SO that processes signals from the transducers 16a and 16c from the pregnant woman's heart, and the fetus's heart, respectively. The monitor also processes signals from the transducer 16b that monitors for contractions in the pregnant woman's uterus. This data are fed to the processor Io determine contraction rates that are sent to the front panel for display.

Processing 50 provides a relatively clean detection of the fetal heartbeat by eliminating major sources of noise in the fetal heartbeat si goal, e.g., the relatively strong acoustic energy components contributed to the detected fetal heartbeat caused by the pregnant woman's heartbeat. In some embodiments, acoustic energy components from uterine contractions could also be filtered from the detected fetal heartbeat acoustic energy.

Referring to Fl(S, 5, processing of signals from the transducers is shown. The signals from channels 36a, 36c are passed through digital band pass filters S! a, 51 b to filter the signals in the range discussed above, e.g., 18 to 25 Hz for the fetal channel and 8 to 12 Hz for the maternal channel The other ranges above could be used. The component of the pregnant woman's heartbeat that appears in the fetal channel is removed from the fetal signal in the difference block 51c. From the difference block, the signal is fod to s pitch track processor 52. The pitch track processor 52 uses pitch tracking and a principal component analysis to generate waveforms thai can be used to determine heart rates, e.g., in bean rate processor 55 and process the signal Io provide an ECQ from ECG processor 56. These signals can be displayed on display 58.

The modulator 54 takes the output signal from the difference block 5Id and modulates it with a signal in the audible spectrum of human hearing. That is, the modulator adds a carrier to the signal from the difference block 51 ά to provide an output signal that CM be heard by humans. This signal can be converted to an analog representation and tec! to an audio amplifier, to be rendered from a speaker 58b, etc. Details of processing are discussed below.

Referring to FiGS. 6A-6E through 8A-8C, collectively FIGS. 6-8, details of construction for an acoustic transducer "button" 16c transducer to acquire sound waves in the audible spectrum from the fetal heart are shown, A similar arrangement can be used for the transducer 16a to acquire the maternal heart beat signal and transducer 16b. the tocodynamometcr (TOC-O) transducer to detect maternal contractions, as further described below.

57 Transducer i 6c is a relatively small, self-adhering, device that, in some implementations, is wireless. Transducer 16c is attached to the epidermis of the maternal abdomen, via a layer of an adhesive, e.g., an adhesive tape 6I₅ in particular a double-sided adhesive, which in addition to providing for attachment of the transducer 16c to the epidermis also provides acoustic impedance matching between the epidermis and a piezoelectric membrane that detects acoustic energy in the transducer. The transducer 16c captures acoustic energy that emanates from the maternal abdomen, through the uterus.

Referring to FIGS, 6A-6E, collectively, FIO. 6, the acoustic transducer "button" 16c includes a base member 60. The base member 60, as depicted in FIG. 6A, includes a frame arrangement 62 that supports bosses 64 to carry a circuit board (not shown} that supports signal preconditioning circuits, as discussed in FIG. 9.

FiCL 6 A depicts an aperture 66 in a bottom portion 60a of the base 60. A polymer membrane 68 covers a substantial portion of the aperture όάa. The polymer membrane 68 is sandwiched between a pair of electrodes over the opposing major surfaces of the polymer membrane 68, A pair of wires (not shown), for example, are attached to the electrodes of the polymer 68, Bosses are provided in the base 60 to elevate a circuit board above the plane of the bottom of the base 60 to provide clearance for wires, that couple to the electrodes OB the polymer membrane 68.

As shown in FIG. 6B, the polymer membrane 68 is disposed through a cavity 65 in the bottom of the base 60, such that the polymer membrane 68 rests within but is not interfered with by sides of the base 60 that form cavity 65, The cavity can be eliminated. For instance, depending on manufacturing constraints other configurations such as connecting the FCB to the membrane via electrodes provided through the base may be preferred, hi addition a foam type material can occupy the cavity, e.g., the cavity can be filled with another material, e.g., an acoustic foam material The polymer membrane 68 has a major surface that is contacted by the double-sided adhesive tape 61 on what will be the outside of the base 60, as shown in FlG, 6C, and a second majυr surface that is within the transducer.

The adhesive layer 61 is provided on the bottom of the base and over the outside surface of the polymer membrane 68. In genera!, the adhesive layer contacts the polymer membrane 68 on the outside, major surface, thus securing the polymer membrane 68 into the transducer. The adhesive 69 is provided as a double-sided adhesive medical-grade tape of a 4.5 mil double coated polyester tape, coated on both sides with a hypoallergenie,

IS pressure sensitive synthetic rubber based adhesive on a 1 mil transparent polyester carrier, with a release liner silicone coated 60 Ib bleached Kraft paper. This tape is ethylene oxide, gamma and autoclave process tolerant. One suitable product is Tape No. 987? from 3M Corporation Minneapolis MN. Other adhesive tapes and adhesives could be used. ϊn conventional approaches, as mentioned above an acoustic match is provided by a gei that is applied on the maternal abdomen. Typically, the operator covers a region of the abdomen with the gel (a slippery, non-sticky clear gel) and moves the ultrasonic sensor around the area to scan the area. Alternatively, the conventional ultrasonic sensor can be affixed with a belt that is worn around the woman. The Licit is cumbersome and especially inaccurate (since often the sensor slips off of its target) and it has Io be removed prior to surgery or emergency procedures. in contrast, the adhesive tape 61 secures the polymer membrane to the transducer !6a, holding one major surface of the polymer, e.g., the outer surface of the polymer, while permitting the other major surface of the polymer 68 to be free to vibrate in the cavity 65 of the transducer. The adhesive tape 61, as discussed above, panicles acoustic coupling between the polymer 68 and the maternal abdomen, hi some embodiments, .material cars be interposed between the tape and the polymer membrane for additional acoustic impedance matching. Here the tape 69 provides acoustic impedance matching, while securing the polymer 68 to the transducer 16c mid also securing the transducer 16c to the abdomen of the patient.

As depicted in FiG. 6D, a snap member 71 is disposed on an inner portion of the sidevvaU of the base member 60, to fasten a dome cap member 74 (FIGS. /A-7D) to the base member 60. Here five additional snap members are disposed about the base, adjacent to the bosses, as denoted by "S," FIG. 6E shows a side view of the base member 60 from a side opposing the slot 69.

Refcrπng to FIGS. 7A-7D, collectively FIG. 7, the dome cap member 80 is illustrated. The dome cap 80 has a generally convex outer surface, as depicted in FIG. 7A. The dome cap member supports a set of binding posts 82 that align with the base member 80 (FIG, 6} to secure the circuit board (not shown) inside the dome cap 80 and urge the circuit board against the bosses 64 on the base member 60, as depicted in FIG. 7C. The dome cap SO has a generally convex outer surface to increase the mechanical integrity of the transducer housing. FIGS, ?C and ID depict details of the snap receptacle member 84 to secure the dome 80 to Um base (SO, Other fastening arrangements are possible including gluing, screw fastening, welding and so forth.

The base 60 and the dome 80 are comprised of a generally translucent material. One type of material for the dome 80 and base 60 is ΛBS, especially medically approved ABS, ABS is aplastic, especially any of a class of plastics based on acryionitrile-bistadienc- styrcrse copolymers. ABS has sufficient strength to support the weight of a pregnant women should she roll over onto the transducer, is medically approved, and is translucent. Other types of materials, especially plastics having sufficient strength and preferably translucence or transparency could be used.

By using a translucent (or transparent) plastic, an optical type of indicator, such as a light emitting diode (LED) can be coupled to the circuitry inside the device. One or a series of LE D" s CM be used to indicate status and health of the transducer, as discussed below. The LELTs could also be outside of υr mounted into the base or dome the device.

Referring to FIGS, 8A-8C, the assembled transducer 16c is illustrated with the base member 60 secured in place to the dome cap 8(L with the polymer membrane 68 exposed on the bottom with the adjacent cavity 66.

Referring to FIGS, 9A-9B, collectively FlG. 9, an alternative construction is shown. Here the base member 60' has a aperture 66' that is in a generally "Y" shape, e.g., with three rectangular aperture regions converging together, in which are disposed three (3) polymer membranes 68a~68c. The membranes 68a-6Sc improve sensitivity and can be electrically coupled in series to increase the overall voltage produced from the patient or hi parallel to increase the amount of charge and hence reduce the input impedance for the high impedance amplifier.

The polymer membrane 68 or 68a-68e can be comprised of any suitable polymer material that exhibits piezoelectric properties. Certain polymer and copolymer materials such as poiyvinyidene fluoride (PVDF) have long repeating chains of '⁴CHj ^■■ CH₂" molecules thai when "orientated" provide a crystalline structure and a net polarization. Such a sheet of orientated material disposed between a pair of electrodes, for example, can detect mechanical energy by producing a net charge or produce mechanical energy by application of charge.

Films can be obtained from Measurement Specialties Inc. Valley Forge PA as pail No. SDT! -028k. which is equivalent to DT1-O28k whose properties are in the table below, but without a protective urethane coating. This is a 028 micron thick polymer sheet with Silver ink electrodes although NiCu-alloys could be used. Leads can be placed on separately or can be provided by the manufacturer. Leads can be attached by compressive clamping, crimps, eyelets, conductive epoxy or low temperature solders and so forth.

Number A B C X⁾ Λ

FJIΪΪI electrode fife) e ieetrode iickncss Cap&c

DT ! -02SK .64 (16} .484 (12} LfG (4 ! ) J . 19 (30) 40 1.38 nf

Where dimensions A-E are in millimeters (mm), F is capacitance (nf) πano farads and where A and C are the width and length of the film, B and D arc the width and length of the electrode and E is the thickness of the PVDF polymer. Other thickness, .sizes and types of piezoelectric PYDF polymer could be used,

In one mode of operation, mechanical energy in the form of acoustic energy from the pregnant woman (detected fetal and maternal heartbeats or detected contractions) impinge upon the combination of electrodes and sheet of material causing mechanical deforming of the orientated crystalline structure of the sheet. This mechanical deformation produces a voltage potential across the sheet of material, providing a potential difference between the pair of electrodes. This potential difference is amplified by the circuitry on the circuit board, is preprocessed, and transmitted to the monitor 12,

The transducer lόa for measurement of audible spectrum sound waves from the maternal heart can be constructed in a similar manner. This button will be attached to the epidermis, e.g. the precordium, and will sense acoustic waves and send the signal to the interface 36 for processing. In general, the preeordiwm is the externa! surface of the body overlying the heart and stomach, typically, in the case of a pregnant woman, under the left breast ofthe patient,

A tocodynamometcr (TOCO) transducer 16b for measurement of maternal uterine contractions is also constructed in a similar manner. The tocodyuamomeier (TOCX)) transducer 16b like the other transducers is a self-powered device, at bast m wireless applications. The toeodynarnorøeter (TOCX)) transducer 16b is a small self-adhering device that detects contractions ofthe .muscles ofthe pregnant woman's uterus by sensing tightening of the maternal epidermis in the vicinity ofthe uterus. Transducer 16b is similar in construction to the transducers 16a and 16c, and is coupled to the rnorsiior, via one ofthe input channels. The signal rrøra the transducer 16b is processed to provide a measure of the rate of contractions of the uterus.

In an alternative embodiment, the TOCO transducer 16b is a conventional strain gauge, which docs not require the acoustic equipment of the heart beat monitor.

Together, transducers 16a and 16c comprise a transducer system for capturing acoustic energy that can include the fetal heart signal and with the analysis described in FIGS. 4 and 5 can produce an audible and acoustic signal of the fetal heart from which the fetal condition can be ascertained.

I.n addition, the transducer 16a and 16b provide a transducer system that provides signals that when processed provide an indication of the labor status of the pregnant woman, e.g., hem rate and rate of uterine contractions.

The sci of transducers 16a~16e provides minimal discomfort to the pre&nanl woman, complete transparency with regard to the currently employed delivery room ietal monitoring techniques, and minimal and virtually no interference with emergency surgical procedures such as emergency cesarean section, especially with the wireless embodiments.

The wireless communication employed is low-power radio-frequency (RF) signals in compliance with FCC regulations posing no risk (according to contemporary medicals views) to the pregnant woman, the infant, or any technicians and clinicians. One preferred wireless technology employed is low power, Bluetooth'® (Bluetooth® SiG, tec.) wireless technology approved for medical applications.

Referring to FiG. K), circuitry 100 cm the circuit board housed m the transducer 16c ss shown. The circuitry 100 includes a high impedance amplifier 102 that interfaces to wires from the electrodes on the polymer membrane 68, as well as a batten' 104 and a transmitter device 106 (or a analogy driver circuit (not shown) i f the transducer 16c is coupled to the monitor 12 via wires. Also included is an antenna element 10S, here a dφole antenna internal to the transducer, An on-chip antenna device may also be used, Other techniques could be used such as infrared or optical hi a wired implementation, power to the devices could be delivered via wires that attached to the transducer, whereas in the wireless implementation power is provided by a small battery, as shown in FIG. 10.

In one wireless implementation each transducer includes a unique device identifier code ! 05, In operation, each transducer lόa-16c when powered up would first be registered with the monitor 12, e.g., a procedure that stores in the monitor 12 the unique identifier of the transducer that the monitor is Wireless coupled to. Each time the transducer sends data to the raomtor, the transducer includes the transducer identifier, so that the monitor would be certain thai it is processing data from tfie correct transducer, registered for feat monitor, and not irons transducers registered with a different monitor and on a different patient.

The circuitry also includes LEDS, here three being shown that light up to indicate various statuses of the transducer. For instance, using the situation of wireless transducers, the three LEDS, one red, one yellow ami one green, can be used to indicate the statuses ot respectively, "failure", e.g., of a battery, as shown or by failing to receive any output signal from the transmitter; "ready but not registered" by sensing a signal from the transmitter,, which would be in that case a transceiver, which would receive a signal back Irorø the .monitor indicating that it is registered with the monitor; and "working" by sensing the output the transmitter. Alternatively, the 1.,EDs can sense outputs from the amplifier.

Referring to FIG. 11, the high impedance amplifier 102 is used to interface with the polymer sheet 68. Since the polymer sheet 68 is eapacitive in nature, a high input impedance amplifier is used to amplify the voltage potential generated across the polymer sheet prior to transmission (either wireiessly or with wires) to the monitor, The high impedance amplifier 102 has components to set the operating point of the high impedance amplifier 102. The high impedance amplifier 102 includes an operational amplifier 104 having differential inputs one of which receives a portion of the output signal fed back to the inverting input --1NA of the amplifier 104. The signal from the sheet 68 is fed to the non-inverting input -HlNA.

Referring now to FiG. 12, details of the pitch processing block 52 are shown. From the difference block, 5Id (FlCl 5} the signal is fed to pitch track analyzer 12Cx a switch 122, a principal component analysis (PCA) generator 124 and a spacing coefficient, generator 126.

Principal component analysis (PCA) is a linear algebraic transform. PCA is used to determine the most efficient orthogonal basis for a given set of data. When determining the most efficient axes, or principal components of a set of data using PCA, a strength (i.e., an importance value called herein as a coefficient) is assigned to each principal component of the data set.

The pitch track analyzer 120 determines the pitch periods of the input waveform. The signal switch 122 routes the signal to the S⁵CA generator 124 during ars initial calibration period, FCA generator 124 calculates the principal components for the initial pitch period received. PCA Generator 124 sends the first, e.g., 6 principal components for storage 130 auα/or further processing. After the initial period, switch 122 routes the signal from the difference block to coefficient generator 126, which generates coefficients lor each subsequent pitch period. Instead of sending the principal components, only the coefficients are sent, thus reducing the number of bits.

Switch 16 includes a mechanism that determines if the coefficients being used are valid. Coefficients deviating from the original coefficients by more than a predetermined value are rejected and new principal components and hence new coefficients are determined.

The pitch tracking analyzer 120 and the other components mention above are described in U.S. Patent Application Serial No. 10/624,139 filed July 21, 2003, published US-20^Q4-0! 02965-A1 May 27, 2004 by Ezra I, Rapoport incorporated herein by reference in its entirety.

The pitch track analyzer 120 determines the pitch periods of the input waveform. The pitch track analyzer 120 determines trends m the slight changes that .modify a waveform across its pitch; periods including quasi -periodic waveforms like heartbeat signals. !n order to analyze the changes that occur from one pitch period to the next a waveform is divided into its pitch periods using pitch tracking process 53 (FICI 13).

Referring now also to FIG 13 a pitch tracking process 121 receives 121 a an input waveform 75 (FIG. 14A) from difference block 51c to determine the pitch periods. Even though the waveforms of fetal heartbeat are quasi-periodic., a fetal heartbeat still has a pattern that repeats for the duration of the input waveform 75. However, each iteration of the pattern, or "pitch period" (e.g., PP;) varies slightly from its adjacent pitch periods, e.g.. PPo and PP;;. Thus, the waveforms of the pitch periods are similar, but not identical, thus making the time duration for each pitch period unique.

Since the pitch periods in a waveform vary in time duration, the number of sampling points in each pitch period generally differs and thus the number of dimensions required for each vectorized pitch period also differs. To adjust for this inconsistency, pitch tracking analyzer 120 designates 121b a standard vector (time) length, V_L» After pitch tracking process 12! executes, the pitch tracking analyzer 120 chooses the vector length to be the average pitch period length plus a constant, e.g., 40 sampling points. This allows for an average buffer of 20 sampling points on either side of a vector. The result is that ail vectors are a uniform length and can be considered members of the same vector space. Thus,

2-1 vectors are returned where each vector has the same length and each vector includes a pitch period.

Fitch tracking process 121 also designates 121 c a buffer (time) length, B;_.., which serves as an offset and allows the vectors of those pitch periods thai are shorter than the vector length to run over and include sampling points from the next pitch period, As a result, each vector returned has a buffer region of extra information al the end. This larger sample window allows for more accurate principal component calculations (discussed below), hi the interest of storage reduction, the buffer length may be kept to between H) and 20 sampling points (vector elements) beyond the length of the longest pitch period in the waveform,

At 8 kHz, a vector length thai includes 120 sample points ami an offset that includes 20 sampling units can provide optimum results.

PUch tracking process 121 relies on the knowledge of the prior period duration, and does not determine the duration of the first period in a sample directly. Therefore, pitch [racking process V21 determines I2U1 an initial period length value by finding a real "eepstmm" of the first few pitch periods of the heartbeat signal to determine the frequency of the signal. A cepstrum is an anagram of the word "spectrum^* and is a mathematical function that is the inverse Fourier transform of the logarithm of the power spectrum of a signal. The cεpstrum method is a standard method for estimating the iirackrnemal frequency (and therefore period length) of a signal with fluctuating pitch.

A pitch period can begin at any point along a waveform, provided it ends at a corresponding point. Pitch tracking process 121 considers the starting point of each pitch period to be the primary peak or highest peak of the pitch period.

Pitch tracking process 121. determines 121 e the first primary peak 77. Pitch tracking process 111 determines a single peak by taking the input waveform, sampling the input waveform, taking the slope between each sample point and taking the point sampling point closest to mo. Pitch tracking process 121 searches several peaks within an expectation range and Lakes the peak with the largest magnitude as the subsequent primary peak 77. Pitch tracking process 121 adds 121 f the prior pitch period to ihe primary peak. Pitch tracking process 12] determines 12 Ig a second primary peak 81 locating a maximum peak from a series of peaks 79 centered a time period, P, (equal to the prior pitch period, PPQ) from the first primary peak 77. The peak whose time duration from the primary peak 77 is closest to the time duration of the prior pitch period FP,;, is determined to be the ending point of that period (PP]) mid the starting point of the next (PPi). The second primary peak is determined by analyzing three peaks before or three peaks after the prior pitch period irøm fee primary peak and designating the largest peak, of those peaks as the second peak 82.

Process 121 vectorizes

the pitch period. Pilch tracking processor 120 makes .!2Ij the seeυiid primary peak the first primary peak of the next pitch period and recursively executes, e.g., back to 1.2 If, returning a set of vectors. That is, pitch tracking process 120 designates 12 Ij the second primary peak as the first primary peal' of the subsequent pitch period and reiterates (12 If)-(12. Ij).

Each set of vectors corresponds to a vectorized pitch period of the waveform, A pitch peπod is vectorized by sampling the waveform over that period, and assigning the .^""' sample value to the i^th coordinate of a vector in Euclidean ^-dimensional space, denoted by IR \ where the index i runs from I to «, the number of samples per period. Each of these vectors is considered a point in the space ^■& '\

FKl 14B shows an illustrative sampled waveform of a pitch period. The pitch period includes 82 sampling points (denoted by the dots lying cm the waveform) and thus when the pitch period is vectorized, the pitch period can be represented as a single point in mi 82 (or higher) "dimensional space.

Thus, pitch tracking processor 120 identifies the beginning point and ending point of each pitch period. Pitch tracking processor 120 also accounts for the variation of time between pitch periods. This temporal variance occurs over relatively long periods of time and thus there are no radical changes in pitch period length from one pitch period to the next. This allows pitch tracking process 62 to operate recursi VeIy₅ using the length of the prior period a.s an input to determine the duration of the next.

Fitch tracking processor IZQ can be stated as the following recursive function;

The function Jϊp.p ') operates on pairs of consecutive peaks p m\ά p ' in a waveform, recurring to its previous value (the duration of the previous pitch period) until it finds the peak whose location in the waveform corresponds best to that of the first peak in the waveform. This peak becomes the first peak in the next pitch period, hi the notation used here, the letter p subscripted, respectively, by "prev," "Ww," "«etf" and "#," denote lhe previous, the current peak being examined, the next peak being examined, and the first peak in the pilch period respectively. The value "5 " denotes the time duration of the prior pitch period, and d(p,p ') denotes the duration between the peaks/; and p '.

B. Principal Component Analysis

Principal component analysis is a method of calculating an orthogonal, basis for a given set. of data points that defines a space in which any variations in the data arc completely uncorreiatcd. PCA can be used as a compression technique to store pitch periods from the pitch tracking processor for detailed analysis. The symbol "$ "" is defined by a set of 0 coordinate axes, each describing a dimension or a potential for variation m the data. Thus, n coordinates are required to describe the position of any point. Each coordinate is a scaling coefficient along the corresponding axis, indicating the amount of variation along that axis that the point, possesses. An advantage of PCA is that a trend appearing to spars multiple dimensions in 31 '^'' can be decomposed into its "principal components," i.e.. the set of eigen-axes that most naturally describe the underlying data. By implementing PCA, it is possible to effectively reduce the number of dimensions. Thus, the total amount of inibrraation required to describe a data set is reduced by using a single axis to express several correlated variations.

For example, FIG. øA shows a graph of data points in 3-dimensions. The data ii^ F(G, 6B are grouped together forming trends. FIG 6B shows the principal components of the data in FIG. δA. FIG. 6C shows the data redrawn in the space determined by the orthogonal principal components. There is no visible trend in the data in FJCJ, όC as opposed to FLGS. 6 A and 6B. In this example, the dimensionality of the data was not reduced because of the low-dimensionality of the original data. For data in higher dimensions, removing the trends in the data reduces the data's dimensionality by a factor of between 20 and 30 in routine speech applications. Thus, the purpose of using PCA in this method of compressing speech is to describe the trends in the pitch-periods and to reduce the amount of data required to describe speech waveforms.

Referring to FlG 15. principal components process 124 determines (S.52} the number of pitch periods generated from pitch tracking process 121. Principal components process 124 generates (154) a correlation matrix.

^'The actual compulation of the principal components of a waveform is a weli-defmed mathematical operation, and can be understood as follows. Given two vectors x and y, xy^; is the square matrix obtained by multiplying x by the transpose of y. Each entry [xy^'%- is the product of the coordinates x,- aiκl» Similarly, if X and Y are matrices whose rows are the vectors s. and y}, respectively, the square matrix XY'' is a sum of matrices of the form

XY^* can therefore be interpreted as an array of correlation values between the entries m the sets of vectors arranged in X and Y. So when X=Y, XX^r is an "autocorrelation matrix," in which each entry |XX%- gives the average correlation (a measure of similarity) between the vectors x, and x_;. The eigenvectors of this matrix therefore define a set of axes in " corresponding Io the correlations between the vectors in X. The eigen-basis is the .most natural basis in which to represent the data, because its orthogonality implies that coordinates along different axes are uneorrelated, and therefore represent variation of different characteristics in tlie underlying data,

Principal components process 124 determines (156) the principal components from the eigenvalue associated with each eigenvector. Each eigenvalue measures the relative importance of the different characteristics in the underlying data. Process 124 sorts (158) the eigenvectors in order of decreasing eigenvalue, in order to select the several most important eigeπ-axes or '"principal components" of the data.

Principal components process 124 determines { 160) the coefficients for each pitch period. The coordinates of each pitch period in the new space are defined by the principal components. These coordinates correspond to a projection of each pilch period onto the principal components. Intuitively, any pitch period can be described by scaling each principal component axis by the corresponding coefficient for the given pitch period, followed by performing a summation of these sealed vectors. Mathematically, the projections of each vectorized pitch period onto the principal components are obtained by vector inner products:

In this notation, the vectors x and x' denote a vectorized pitch period in its initial and PCA representations, respectively. The vectors e_t- are the ith principal components, and the inner product e^x is the scaling factor associated with the ith principal component. Therefore, if any pitch period can be described simply by the scaling and summing the principal components of the given set of pitch periods, then the principal components and the coordinates of each period in the new space are ail that is .needed to rcconst.ru.et any pitch period and thus the principal components and coefficients axe the compressed form of the original heartbeat signal, In order to reconstruct any pitch period of/? sampling points, n principal components arc necessary.

In the present case, the principal components are the eigenvectors of the matrix SS', where the /til row of the matrix S is the vectorized Hh pitch period in a waveform Usually the first 5 percent of the principal components can be used to reconstruct the data and provide greater than 9? percent accuracy. This is a general property of quasi-periodic data. Thus, the present method can be used to find patterns that underlie quasi-periodic data, while providing a concise technique to represent such data. By using a single principal component to express correlated variations in the data, the dimensionality of the pitch periods is greatly reduced. Because of the patterns that underlie the quasi-periodicity, the number of orthogonal vectors required to closely approximate any waveform is much smaller than is apparently necessary to record the waveform verbatim.

Another type of analysis is the complex wavelet transform, as described in Duai- lYee Complex Wavelet Transform, Ivan VV. Selesnick. et al._s IEEE Signal Processing Magazine 123 November 2005, which is incorporated herein in its entirety.

The invention ears, be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations thereof Apparatus of the invention can be implemented in a computer program product tangibly embodied m a machine-readable storage device for execution by a programmable processor; and method aciions cm be performed by a programmable processor executing a program of instructions to peribrra functions of the invention by operating on input data and generating output.

The invention can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least on<? output device. Each computer program can be implemented in a high-level procedural or object oriented programming language, or in assembly or machine language if desired; and in any case, the language can be a compiled or interpreted language. Suitable processors include, by way of example, both general and special purpose microprocessors. Generally, a processor will receive instructions and data from a read-only memory and/or a random access memory. Generally; a computer will include one or more mass storage devices for storing data files: such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optkai disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non- volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPRON-I, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD ROM disks. Any of the foregoing can be supplemented by. or incorporated in. ASICs {application-specific integrated circuits).

A number of embodiments of the invention have been described, Other embodiments are wuhin the scope of the following claims.

Claims

WJIAT IS CLAIMED IS:

1. A fetal heart monitor device comprises: a channel to receive a first signal representative of acoustic energy including a fetal heart beat; a computing device, composing: a processor; a memory operative])' coupled to the processor; and non-volatile storage operative!}-' coupled to the processor, the non-volatile storage storing a computer program comprising instruction to cause the processor to: analyze the first electrical signal and output an electrical signal representative of acoustic energy emitted during the fetal heartbeat.

2. The device of claim 1 further comprising: a channel to receive a second signal representative of mechanical strain, energy of uterine contractions; and the program comprises instructions to: process the second electrical signal into an indication of maternal uterine rates of contraction.

3. Hie device of claim i wherein instructions to process further comprises instructions to: a channel to receive a third signal representative of acoustic energy principally from a maternal heartbeat; and process the first and third electrical signals to provide an electrical signal representative of acoustic energy principally of the fetal heartbeat and a signal of the maternal heartbeat.

4. The device of claim 1 further comprising instructions to: render the electrical signal representative of the fetal heartbeat on an output device.

5. The device of claim 1 wherein the monitor further comprises; an audio speaker and the electrical signal is rendered by the speaker to produce an audio representation of the fetal heartbeat.

6. The device of claim 1 wherein the rnomlor further comprises: a display aiκl the electrical signal is rendered by the display to produce representation of the fetal heartbeat.

7, The device of claim i wherein the monitor further comprises: a display and the electrical signal is rendered hy the display to provide a representation of the fetal heartbeat rate,

8, The device of claim 1 further comprising: an acoustic transducer comprising a polymer that exhibits piezoelectric properties, and which converts acoustic energy into the first and second signals.

9. The device of claim 2 further comprising: three acoustic transducers each comprising a polymer that exhibits piezoelectric properties, and which converts acoustic energy into the first second and third signals.

10. The device of claim 8 the transducer, comprises circuitry to wireSessiy transmit data to the monitor; and the monitor further comprises; circuitry to receive the wirelessly transmitted data.

11, The device of claim 8 wherein the transducers comprises a polymer sheet of polyvrnyldene fluoride and/or copolymers thereof.

12, A method of monitoring fetal heart beat, the method comprises: receiving over a first channel, a first signal representative of acoustic energy principally fwm a .maternal heartbeat; receiving, over a second channel, a second signal representative of acoustic energy including a fetal heart beat; processing the first and second electrical signals into an electrical signal representing acoustic energy principally of the fetal heartbeat.

13 , The method of claim 12 further comprises: converting acoustic energy representative of maternal uterine contractions into a third electrical signal.

14. The method of claim 12 wherein processing further comprises: processing the first and second electrical signals to provide the electrical signal representative of acoustic energy principally of the fetal heartbeat, the second signal to provide a signal representative of the maternal heart ami the third signal to provide a signal representative of maternal uterine contractions,

15. The method of claim 12 further comprising; rendering the electrical signals representative of the fetal heartbeat, maternal heartbeat and uterine contractions on an output device.

16. A fetal heart monitor device comprises; a channel to receive a first signal representative of acoustic energy principally from a maternal heartbeat and a second signal representative of acoustic energy including a fetal heart beat; and circuitry to process the first and second electrical signals into an electrical signal representing acoustic energy principally of the fetal heartbeat.

1 ?. The device of claim 16 further comprising: a channel to receive a third signal representative of acoustic energy of uterine contractions; and circuitry to process the third electrical signal into an indication of maternal uterine rates of contraction.

38, The device of claim .16 farther comprising circuitry to: render the electrical signal representative of the fetal heartbeat on an. output device,

19. The device of claim .16 further comprises: circuitry to modulate the fetal heart tone into the audible frequency range; an audio speaker to render an audio representation of the fetal heartbeat; and a display to render a visual representation of the fetal heartbeat: a display to render a value indicative of fetal heartbeat rate.

20. An acoustic transducer comprises; a base member; a polymer sheet having a pair of electrodes disposed over major, opposing surfaces of the polymer sheet, the polymer sheet disposed adjacent an exterior portion of the base member; a cap affixed to the base member; and electrical circuitry carried by the acoustic transducer and coupled to the electrodes on the polymer sheet.

21. The acoustic transducer of claim 20 wherein the circuitry is disposed between the base and the cap.

22. The acoustic transducer of claim 20 wherein the cap has a convex surface.

23. Hie acoustic transducer of claim 20 wherein the cap has a convex surface and is secured to the base with, snaps.

24. Tl)O acoustic transducer of claim 20 wherein the cap and the base member are secured together with glue or welded,

25. The acoustic transducer of claim 20 wherein the cap and the base member are secured together

26. The acoustic transducer of claim 20 wherein base has an aperture and live polymer sheet is supported in the aperture by attaching a securing member to one of the major surfaces of the polymer, the one major surface being on aa external surface of the aco ustle iransd ueer,

27. The acoustic transducer of claim 20 wherein an exterior surface of the base member has an adhesive layer thereon to adhere the transducer to epidermis of a subject.

28. The acoustic transducer of claim 20 wherein an exterior surface of the base member has an adhesive layer thereon to support an outer one of the major surfaces of the polymer and to adhere the transducer to epidermis of a subject.

29. The acoustic transducer of claim 20 wherein the adhesive layer provides an acoustic impedance coupling between the outer one of the major surfaces of the polymer and epidermis of the subject.

30. The acoustic transducer of claim 20 wherein the adhesive layer is a double- sided tape.

31. ^'The acoustic transducer of claim 20 wherein the circuitry comprises a transmuting device to wirelessly transmit signals from the transducer.

32. The acoustic transducer of claim 20 wherein the circuitry comprises: a low noise, high impedance amplifier coupled to receive a voltage potential produced across electrodes of the polymer sheet: and a transmitting device coupled to the output of the amplifier to wirelessly transmit an output signal irom the transducer.

33. The acoustic transducer of claim 20 wherein the circuitry comprises circuitry to couple wires or cables to output signals from the transducer,

34. The acoustic transducer of claim 20 wherein the circuitry comprises; a low noise, high impedance amplifier coupled to receive a voltage potential produced across electrodes of the polymer sheet; and a connector to couple signals from the amplifier to the wires or cables.

35. The acoustic transducer of claim 26 wherein the aperture in the base member is a generally rectangular aperture in a substantial portion of the base member.

36. The acoustic transducer of claim 26 wherein the aperture m the base member is a generally Y-shaped aperture having three regions, the aperture in a substantial portion of the base member; and wherein the acoustic transducer comprises: an additional pair of polymer sheets, with the polymer sheet and the addition pair of polymer sheets disposed in the three regions of the aperture.

37. The acoustic transducer of claim 20 wherein the base member and cover are secured together by at least, one of the following: a plurality of snap latches on one of the cover and base that mate with receptacles on the other one of the cover and base to secure the base to the cover gluing, screw fastening, and welding.

38. The acoustic transducer of claim 20 wherein the transducer body is a round shape.

39. The acoustic transducer of claim 2(5 wherein, the transducer is for heart monitoring.

40. "flie acoustic transducer of claim 20 wherein the polymer sheet is polyvinyldene fluoride and/or a co-polymer thereof.

41. The acoustic transducer of claim 20 wherein the base and cover are comprised of a relatively strong plastic materia! that is sufficient in strength to support the weight of a pregnant woman.

42. The acoustic transducer of claim 20 wherein the base and cover are comprised of an ABS plastic any of a class of plastics based on aerylønitriie-butadiene- styrene copo I y m ers .

43. ^'The acoustic transducer of claim 20 wherein the base has an aperture and the polymer member is disposed within the aperture of the base.

44. The acoustic transducer of claim 20 wherein the base has an aperture filled with an acoustic foam materials and the polymer member is disposed within the aperture of the base.

45. An acoustic transducer comprises: a base member having an aperture; a polymer sheet comprised of polyvinyldetie fluoride and/or a co-polymer thereof, the sheet having a pair of electrodes disposal over major, opposing surfaces of the sheet, with the sheet disposed m the aperture in the base member; a cap affixed to the base member; electrical circuitry disposed in the acoustic transducer and electrically coupled Io the electrodes on the sheet, the circuitry comprises a transmitter to transmit signals from the polymer sheet; a !GΛV noise, high impedance amplifier coupled to receive a voltage potential produced across electrodes of the sheet; and a transmitting device coupled to the amplifier to wirelsssly transmit an output signal from the amplifier.

46. The acoustic transducer of claim 45 wherεirs the cap has α convex surface.

47. The acoustic transducer of claim 45 wherein the sheet is supported in the aperture by attaching an adhesive to one of the major surfaces of the polymer, the one major surface being on an external surface of the acoustic transducer.

48. The acoustic transducer of claim 45 wherein the adhesive layer adheres the transducer to epiderrais of a subject.

49. The acoustic transducer of claim 45 wherein the adhesive layer provides an acoustic impedance coupling between the outer one of the major surfaces of the polymer and epidermis of the subject.

50. The acoustic transducer of claim 45 wherein the adhesive layer is a double- sided tape.

51. The acoustic transducer of claim 45 wherein the aperture m the base member is a generally rectangular aperture in a substantial portion of the base member.

52. The acoustic transducer of claim 45 wherein the aperture in. the base member is a generally Y-shaped aperture having three regions, the aperture m a substantial portion of the base member; and wherein the acoustic transducer comnrises: an additional pair of polymer sheets, with the polymer sheet axsd ihe addition pair of polymer sheets disposed in the three regions of the aperture.

53. A method comprises; converting acoustic energy representative of a maternal heartbeat and a fetal heartbeat into a first electrical signal; processing the first electrical signal to provide an electrical signal principally representative of the fetal heartbeat; and determining pitch periods of the signal principally representative of the fetal heart beat.

54. The method of claim 53 further comprising: converting acoustic energy representative principally of a maternal heartbeat into a second electrical signal; processing the processing the first and the second electrical signals to provide the electrical signal principally representative of the fetal heartbeat.

55. The method of claim 53 wherein processing further comprises: rendering the electrical signal principally representative of the fetal heartbeat on an output device.

56. The method of claim 53 further comprising: determining principal components of determined pitch periods of the signal principally representative of the fetal heartbeat.

57. The method of claim 53 further comprising: modulating the electrical signal principally representative of the fetal heartbeat with a signal in the audible spectrum of human hearing.

58. Hie method of claim 5^*7 wherein determining pitch periods further comprises". determining an initial period length value of the signal principally representative of the fetal heartbeat by finding a cepstrum of the first few pitch periods of the signal principally representative of the fetal heartbeat to determine the frequency of the signal.

59. The method of claim 57 wherein determining pitch periods further comprises; determining a beginning and ending point of each pitch period m the signal principally representative of the fetal heartbeat.

60. The method of claim 59 wherein determining pitch periods further comprises; determining a variation of time durations between pitch periods; and using the length of a prior period as an input to determine the duration of a subsequent pitch period.

61. The method of claim 59 further comprising; applying principal component analysis to the determined pitch periods Io compress data representing the determined pitch periods,

62. A computer program product residing on a computer readable medium for detecting fetal heartbeat energy, comprises instructions to cause a monitor to: convert acoustic energy representative principally of a maternal heartbeat into a first electrical Signal; convert acoustic energy representative of a maternal heartbeat and a fetal heartbeat into a second electrical signal; process the first and second electrical to provide an electrical signal principally representative of the fetal heartbeat; and determine pitch periods of the signal principally representative of the fetal heart beat.

63. The computer program product of claim 62 further comprising instructions Ur, con vert acoustic energy representative of maternal uterine contractions into a third electrical signal.

64. The compute? program product of claim 62 further composing instructions to; render the electrical signal principally representative of the fetal heartbeat on an output device.

65. The computer program product of claim 62 farther comprising instructions to: determine principal components of determined pitch periods of the signal principally representative of the fetal heartbeat.

66. The computer program product of claim 62 foriher comprising instructions to: modulate the electrical signal principally representative of the fetal heartbeat with a signal in the audible spectrum of human hearing.

67. The computer program product of claim 62 further comprising instructions to: determine an initial period length value of the signal principally representative of the fetal heartbeat by finding a eepslmm of the first few pitch periods of the signal principally representative of fee fetal heartbeat to determine the frequency of the signal,

68. Hie computer program product of claim 62 further comprising instructions to: determine a beginning and ending point of each pitch period in the signal principally representative of the fetal heartbeat.

69. The computer program product of claim 62 further comprising instructions to; determine a variation of iiroe durations between pitch periods; and use the length of a prior period as an input to determine the duration of a subsequent pitch period.

70. An apparatus comprises: circuitry to convert acoustic energy representative principally of a maternal heartbeat into a first electrical signal; circuitry to convert acoustic energy representative of a maternal heartbeat and a fetal heartbeat into a second electrical signal; circuitry to process the first and second electrical to provide ars electrical signal principally representative of the fetal heartbeat; and circuitry to determine pitch periods of the signal principally representative of the fetal heart beat. The apparatus of claim 70 further comprising: circuitry to convert acoustic energy representative of maternal uterine contractions into a third electrical si ^■togn¹-al.

72, The apparatus of claim 70 further comprising: circuitry to render the electrical signal principally representative of the fetal heartbeat on an output device.

73, ^"The apparatus of claim 70 further comprising: circuitry to determine principal components; of cleterrnisecl pitch periods of the signal principally representative of the fetal heartbeat; circuitry to modulate the electrical signal principally representative of the fetal heartbeat with a signal in the audibie spectrum of human hearing.

74, The apparatus of claim 70 further comprising: circuitry to determine an initial period length value- of the signal principally representative of the fetal heartbeat by finding a cepsirum of the first few pitch periods of the signal principally representative of the fetal heartbeat to determine the frequency of the

75. The apparatus of. claim 70 further comprising: circuitry to determine a beginning and ending point of each pitch, period in the signal principally representative of the fetal heartbeat.

76. The apparatus of claim 70 further comprising: circuitry to determine a variation of time durations between pitch periods; and circuitry to use the length of a prior period as an input to determine the duration of a subsequent pitch period; and store the compressed representation of the determined pitch periods.

77. The apparatus of claim 70 further comprising: circuitry to determine a variation of time durations between pitch periods; and circuitry to use the length of a prior period as an input to determine the duration of a subsequent pitch period; and circuitry to apply principal component analysis to the determined pitch periods to compress data representing the determined pitch periods; and store the compressed representation of the determined pitch periods,

IB. The apparatus of claim 70 further comprising: circuitry to determine a variation of time durations between pitch periods; and circuitry to use the length of a prior period as an input to determine the duration of a subsequent pitch period; and circuitry to apply principal component analysis to the determined pitch periods to compress data representing the determined pitch periods; circuitry to process the determined pitch periods to provide a representation; compress the representation of the determined pitch periods; and store the compressed representation of the determined pitch periods.

79. The apparatus of claim 70 further comprising: circuitry io store a compressed representation of the determined pitch periods,

8⁽5. A method of acoustic monitoring comprises: transducing acoustic energy from a first acoustic transducer attached to a first location on a patient the acoustic energy from the first transducer, comprising desired acoustic energy to be monitored and interfering acoustic energy; transducing acoustic energy from a second acoustic transducer, attached to a second, different location on a patient, the acoustic energy from the second transducer, comprising desired acoustic energy to be monitored and interfering acoustic energy; converting the acoustic energy sensed at the first and second locations ink? first and second electrical signals; processing the first and second electrical signals to digitally remove interfering acoustic energy present in the second signal to provide an electrical signal representative of the acoustic signal that is being monitored.

81. The method of claim S⁽I wherein the interfering acoustic energy is principally representative of a maternal heartbeat.

82. The method of claim 80 wherein the acoustic energy to be monitored includes acoustic energy representative of a fetal heartbeat; and processing the first and second electrical signals provides the electrical signal representative of the fetal heartbeat.

S3. The method of claim SO further comprising: transducing a plurality of signals from a plurality of transducers, including the first transducer, the plurality of signals representing the acoustic energy to be monitored; and processing the first the plurality of signals along with the second electrical signal to provide the electrical signal representative of the acoustic energy to be monitored.

84. The method of claim S3 wherein the acoustic energy to be monitored. includes acoustic energy representative of a fetal heartbeat; and processing the plurality of signals including the first signal, and second electrical signals provides the electrical signal representative of the fetal heartbeat.

85. A method of monitoring health status of a fetus, the method comprises: transducing acoustic energy from a first acoustic transducer attached to the epidermis about the vicinity of the abdomen of a pregnant woman, the acoustic energy from the first transducer, comprising acoustic energy of a fetal heartbeat and interfering acoustic energy of a .maternal heartbeat; transducing acoustic energy from a second acoustic transducer, attached to the percofdium region of a pregnant woman, the acoustic energy from the first transducer the acoustic energy from the second transducer, comprising the interfering acoustic energy of the maternal heartbeat; converting the acoustic energy sensed at the first and second locations into first and second electrical signals; and processing the first and second electrical signals to provide an output signal representative of the fetal heartbeat,

86. The method of claim 85 wherein the interfering acoustic energy is removed during processing of the first and second signals.

87. The .method of claim S5 wherein processing further comprises: processing at least the second electrical signal to provide a second output signal representative of the maternal heartbeat.

88. The method of claim 85 wherein the second transducer is attached beneath the pereordiiim area of the patient.

89. The method of claim 85 further comprising: converting acoustic energy representative of maternal uterine contractions into a third electrical signal

90. The method of claim 85 further comprising: processing the third electrical signal to provide a signal representative of a rate of maternal uterine contractions.

91. The method of claim 85 wherein the method is applied to monitor fetal heartbeats, the method further comprises: attaching the first transducer to the abdominal region of the patient in a region where the back of the fetus is against the maternal abdominal wall.

92. The method of claim 85 further comprising: rendering the electrical signal representative of the fetal heartbeat on an output device,

93« The method of claim 92 wherein the output device is an audio speaker,

94. The method of claim 92 wherein the output device is a display device that renders an electrocardiogram. 95, The method of elaira 92 wherein the output device is a display device that renders readout of heartbeat rate.

96, The method of claim 93 further comprising: rendering the second output signal representative uf the maternal heartbeat, on an output device

⁽⁾7. The method of claim 9! wherein the acoustic transducers are wireless.

98. The rarfhod of claim 91 wherein the acoustic transducers are coupled to a processing device via cables and/or wires.