WO 2007/130958 PCT/US2007/067906 PASSIVE PHONOGRAPIJY HEART MONITOR BACKGROUND This invention relates to medical monitoring and in particular 1etal heart Fetal heart monit(oring is a diagnostic tool to indicate the overall health status of a fetus. Currently deployed fetal heart monitoring techniques are primarily ut rasound, Doppler-based. With a typical ultrasound Doppler-hased technique, wires are deployed between an, ultra sound transducer unit and processing unit, A skied operator, such as a medical technician or nurse swans or places a transceiver on -te abdomen of the patient, Typically, the oentor covers a region on the abdomen vith a gc2 and moves the uhlrasonic sensor around tei area to scan the area Ahernatively the sensor can be affixed with a bet that is won around the woman. TI he 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 simals are emited firon the transducers and their echo signals are detected by the transceiver and procsed to produce dlava pertaining to the ftal heart rate. Current Doppler based techniques for feal monitoring have several limitations. One limitation of current Dopplerbased techniques is the 'ack of specifciQty for detecting tetai heart tones (FHTs). In cases of maternal tachycardia, the oper ator flay onot be able to differentiate whether the transducer is detecting the fetal or matema! signaland this can have eatastrophic consequences Other limitations pertain to changes in ftal position or station which often require re-positionng of the tramducer which can be time-consuming and result in "hlackout" periods in feta monitoring during which medical personnel do not receive data from monitors that monitor the fetus, Another limitation is the loss of continuous monitoring in a distressed fetus, especially during transition periods, e.g., moving frm a delivery room to an operating room for an emergency Cesarean section procedure. In addition, mnany hospital protocols require detachment of all wires from fetal monitong devices during room transfers Detaching fetal monitors begins another "blackout period." Administration of epidurni anesthesia presents another potential blackoutf period for fetal monitoring, as the transd ucer is frequently removed or displaced during that procedure This, too is a critical tieframe for ttal nitoring, as epidural anesthesia may cause natema hypotension with subsequent fetl bradycardia WO 2007/130958 PCT/US2007/067906 Maternal ambulation has been shown to facilitate labor progress, but current techniques Iypi cally preclude such standing deliveries. A newer noni touring technique known as fetal phonography uses a passive acoustic sensor to capture acoustic energy from the maternal abdomen. Tyicallyt sensor includes a piezoelectrc element, in a paper entitled "Devcinct ofa P o Presur Seso fo a orable Fetal Heart Rate Mi'Vnio" by A llan J. Zucokerwar et a, IEEE TRANSACTIONS ON BIOMEDICALU ENGINEERING VOL 40, NO. 9 SEPTEMNIER 1993 p. 963, the authors described a pressure sensor array mounted on a belt woL by the mother The sensor array uses two polyvvinyldene fluoride elements arranged in a birnorph stuicture, mechanicafly in series and electrically in parallel. SUMMARY According to an aspect of the present invention, a fetal heart monitor device mcludes a channel to receive a first signal representative of acoustic energy principally fom a nsatema! 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 operatively coupled to the processor and non-volatile storage operatively coupled to the processor, the nonvolatile storage storing a computer program including instructions to cause the processor to process the first anid second electrical s into an electrical signal representing acoustic energyprincipal ly of the fetal heartbeat, The following are embodiments within tie 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 an 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 sign 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 to 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 etal heartbeat rate.
WO 2007/130958 PCT/US2007/067906 'he 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 poiyner that exhibits piezoelectri c properties, which converts acoustic energy into the irst and second signals and a strain gauge that provides a third signal representati ve 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 wirelessliv transmit data over the first and second channels to the monitor and the monitor includes circuitry to receive the wirelessly transmitted data, The circuitry to wirelessly transmit data includes radio frequency transmitter circuitry, The circuitry to wirelessly transmit data includes circuitry to trans-nit a unique transducer identification code to the monitor, Each transducer include s a polymer sheet of polyvinyldene fluoride and/or co-polymers thereof According to a father aspect of the present invention, a method otnmonitoring fetal heart beat includes receiving over a first channel, a first signal representative of acoustic energy principally fiom a maternal heartbeat, reccivir, 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 sigm representing acoustic energy prrmcipaliv 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 included 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. h'le 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 wirelessly transmitting data from a pair of transducers disposed on the patient over the first and second channels to provide the first and second signals. 0 WO 2007/130958 PCT/US2007/067906 According to a further 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 incliuding 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 foilowiga are enibodiments 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 imaternal uterine rates of contraction. The device includes ciitry to render the decrical 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 an 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 cnpioyed in the ulrasound transducers. The monitor uses low-cost sensing, transmission, and circuitry components suitable for operation in hospitals, physician oftices, 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 tor these transducer sensor units because the term of use for each transducer sensor unit will not exceed a specified time duration. Hence, normal concems of quLity degradation resulting front 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 thepatient, thus making the resources in a abor-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 4 WO 2007/130958 PCT/US2007/067906 permits sophisticated and accurate fetal signal processing to be employed in the monitor at a relativelyvlow cost, The monitor allows for maternal ambulation ring labor, providing a number of potential benefits. Aceordirng to an additional aspect of the present invention, an acoustic transduice includes a base member, a polymer sheet having a pair of electrodes disposed over rnajor. opposing surfaces of the polyner sheet, the polymer sheet disposed adjacent an exterior portion of the base member, a cap afOxed to the base member and electric cal circuitry carried by the acoustic transducer and coupled to the electrodes on the polymer sheet, The following are 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 are secured to gether. The base has an aperture and the polymer sheet is supported in the aperture in the base by attaching a securing member to one of the major surfaces of the polymer, the one major surface being on an external surface of the acoustic transducer An exterior surface of the base member has an adhesive layer thereon to adhere the transducer to epidernis of a subject. The exterior surface of th1e 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, 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 comprises a transmitting device to wirelessly transmit signals from the transducer. The circuitry includes a low noise, high inpedance amplifier coupled to receive a voltage potential produced across electrodes of the polimer sheet and a transmitting device coupled to the output of the amplifier to tirelessly transmit an output signal from the transducer. The circuitry comprises circuitry to couple wires or cables to output signals fnom 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 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 the base member is a generally Yshaped aperture having three regions, the aperture in 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 base member and cover are secured together by a plurality of snap latches on one o-f the cover and base that mate WO 2007/130958 PCT/US2007/067906 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 poyner sneet is polyvinyidene tfuoride anti/or a co-polymer thereof The base and cover are comprised of a relatively strong plastic material that Is sufficient i strength W support the weight of pregnant woman. The the base and cover are comprised of an ABS plastic any of a class of plastics based on acrvionitrile-butadicne-stvrene copolymers. The base has an aperture and the polymer member is disposed within the aperture of the base. The base has an aperture tilled 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 1of the base According to a fuOrther aspect of the present invention, an acoustic transducer includes a base member having an aperture and a polymer sheet comprise of polyvinyidene 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 i Lie base member, The transducer also includes a cap affixed to the base member and elctrical circuitry disposed in the acoustic transducer and electrically coupled to the electrodes on the sheet, The following are 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 noise high impedance aipli after coupled to receive a voltage potential produced across electrodes of the sheet and a transmitting device coupled to the anplifier to wirelessly 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 extemal 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 inajor surfaces of the polymer and epidermis of the subject. The adhesive layer is a doubIc-sided tape. The circuit includes circitry 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 the base member is a generally Yshaped aperture having three regions, the aperture in a substantial portion of the 6 WO 2007/130958 PCT/US2007/067906 base member and wherein 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 transducer is for heart monitoring. The base and cover are 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 an ABS plastic any of a class of plastics based on acvlonitrile-butadiene-stvrene copolyimers, The base has an aperture filled 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 following advantages. 'he transducers are affixed to the patient, which avoids the need fbr a skilled technician to be present while a monitor attached to the transducers is operating. The transducers can be relatively low cost due to the use of the poyrner as compared to more expensive crystals used in Doppler techniques used with ultrasonic transducers. The transducers use low-cosi sensing, tran missionn, 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, nonnal concerns of quality degradation resulting from extended use are avoided, while maintaining a relatively high level of performIane. The wireless versions of the transducer when employed with a monitor can avoid blackout peods,, the potentially nost dangerous window of timet? during labor since the wireless form allows for constant monitoring. Accurate, wireless monitoring system aids in decreasing labor time by increasing the potential mobility oftle patient, thus making the resources in a labor-and-delivery 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 afetal heartbeat into a second electrical signal and processing the first and second electrical to provide an electrical signal principally representative of the fetal heartbeat. The method fisher includes determining pitch periods of the signal principally representatve of the fetal heart beat.
WO 2007/130958 PCT/US2007/067906 The follow enbodiments are within the scope of the invention. The method further includes converting acoustic energy representative ofnaternal uterine contractions ilto a thTrd electrical signal. The method further in ludes rendering the electrical signal prrsentative 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 inchids modulating the electrical signal principally representative of the fetal heartbeat with a signal in the audible spectrum of hum an hearing The method further includes determining an initial period length value of the signal principal representative of the fetal heartbeat by finding cepstu of the'irst fewv pitch perods 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 pitch period in the signal principally representative of the fetal heartbeat. The method further includes determining a variation of tine durations between pitch 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 ctuipress data representing the determined pitch periods. The method further includes processing the determined pitch periods to provide a representation, compressimg 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 cmt 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 matemal 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 pedods of the signal principally representative of the etal heart heat The fAilowing are embodiments within the scope of the invention, The computer prograrn product further includes instructions to convert acoustic energy representative of maternal uterine contractions into a third electrical signal The computer program product further 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 8 WO 2007/130958 PCT/US2007/067906 periods Of the signal principally representative of the fetal heartbeat, The computer program product further includes instructions to modulate the electrical signal principally representative of the fta] heartbeat with a signal in the audible spectrum of human hearing The computer program product further includes instructions to determinean initial period length value of the signal principally representative of the fetal heartbeat by finding a cepstrtum of the first few pitch periods of the signal principally represettive the feta 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 to determine a variation of time durations between pitch periods and use the length of a prior Period as an iiput to determine the duration of a subsequent pitch period. The computer program product further includes instruction to appiy 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 representtion of the determined pitch periods and store the compressed representation of the determined pitch periods, According to an additional aspect of the present invention, an apparatus includes 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 leta heartbeat into a second electrical signal, circuitry to process the first ana 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 embodinents within the scope of the invention. The apparatus includes circuitry to convert acoustic energy representative of matemal uterine contractions into a third electrical signal. The apparatus inades circuitry to render the electrical signal principally representative of the fetal heartbeat on an output device. The apparats 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 initi al period lengt value of the signal principally representative 9 WO 2007/130958 PCT/US2007/067906 of the fetal heartbeat by finding a cepstrm of the first fw pitch periods of the signal principally representative of the fetal heartbeat to determine the frequency of the signaL Thie apparatus includes circuitry to determine a beginning and ending point of each pitCh period in the signa principal 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 ofa 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 deternined pitch periods to provide a representation, compress the representation of the determined pitch periods, and store the compressed representation of the determined pitch periods. One or muore 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 b avoiding need for relatively expensive crystals commonly employed in the ultrasound transducers. The monitor uses low-cost sensing, transmission, and circuitry components suitable Ir operation in hospitals, physician offices, or home environments. 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 trnsducer sensor unit will not exceed a specifed tine duration. Hence, normal concerns of quality degradation resulting fon extended use arc avoided, while maintaining a relatively high level of performance The monitor avoids blackout periods, eag.. the potentially most dangerous window of time duIng labor since the monitor in the wired and especially the wireless form allows for constant montoring. Accurate, wireless monitoring system aids in decreasing labor time by increasing the potential mobility of the patient, thus taking the resources in a labor-and-delivery unit more v ailble. The monitor uses a pitch period detector, a principal component analyzer and a complex wavelet itlter bank 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 10t WO 2007/130958 PCT/US2007/067906 The monitor allows for maternal anibulation during labor, providing a number of potential benefits. Acfordhing to an aspect of the present invention ai methfod o acoustic iing of "ousiomonitorin includes transducing acoustic energy from a first acoustic transducer attached to a first location on a patient the acoustic energy from the first transducer comnrisina desired acoustic energy to be monitored and interfering acoustic energy transductng 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 convcrting 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 digitally remove interfrinacoustic energy present in the second signal to provide an electrical signal representative ofthe acoustic signal that is being momiorecd. The Rllowing are embodiments within the scope of the invention, The interfering acoustic energy is principally representative of a maternal heartbeat, The acoustic energy to be montored 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 puhirality 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 representatve 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 ftal heartbeat. According to an aspect f the present invention, a method of monitoring health status of a fetus includes transducing acoustic energy from a Irst acoustic transducer attached to the epidermis about the vicinity of the abdomen of a pregnant woman 4 the acoustic energy frm 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 percordiumxi region of a pregna 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 I i WO 2007/130958 PCT/US2007/067906 energy sensed at the first and second locations into first and second electrical signals anid processing the first and second electrical signals to provide m output Signal representative of the fetal hearbeat. The interfering acoustic energy is removed during processing of the flrst and second signals. Theprocessing inchides processing at least the second electr signal to providea second output signal representative of the maternal heartbeat. The second transducer is attached beneath the percordiumn area of the patient. [he method includes converting acoustic energy reprsentative of maternal uteine contractions into a third electrical signal The method includes processing the third electrical spinal to pro vide a signal representative of a rate of matemal 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 wall. The method includes rendering the electrical signal representative of the fetal heartbeat on an output device. The output device is an audio speaker. The output device is a dispIay device that renders an electrocardiogram. The output device is a displaV device that renders readout of heartbeat rate. The method includes rendering the second output signal representativee of the maternal heartbeat on an output device. The acoustic transducers are wireless. The acoustic transducers are coupled to a processing device via cables and/or wires: 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 ommpared to currently employed ultrasound based monitors by avoiding need for relatively expensive crystals cormnonly enrloved in the ultrasound transducers; The monitor uses low-cost sensing transmission, and circuitry components suitable for operation in hospitals, physician otces, 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 unit will not exceed a specified time duration; Hence nominad concerns of quality degrade uon resulting from extended use are avoided, while maintaining a relatively high level of performance. The monitor avoids hiackout periods, e.g, the potentially most dangerous window of time during labor since the monitor in the wired and especially the wireless form 12 WO 2007/130958 PCT/US2007/067906 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 laboriand-deiivery unit more avaiable le monitor uses a pitch period detector and a pincipa Component analyzer to analyze signals from the sensors. This pernits 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 potentialbenefits. The details of one or more embodiments of the invention are set forth in the accompanytng drawings and. 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 DRAW INGS FIG I is a block diagram of a monitoring scheme. FiG 2 is a block diagram of fetal monitor device used to monitor fetal cardiac activity FIG 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-6F-SA-8C (collectively, FIGS, -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 ahemnate pattern for a piezoelectic sensor element. FIG 1 () is a block diagram of circuitry used in the sensors. FIG II is a schematic of a high impedance amplifier used with the sensors of FIGS. 6&8. FIG 12 is a block diagram depicting details of pitch processing FIG 1 3 is a flow chart depicting pitch processing FIGS. 14A and 14,13 are diagrams useful in understanding processing of fetal and maternal heartbeat signals FI1 15 is a flow chart depicting principal component analysis.
WO 2007/130958 PCT/US2007/067906 DETAILED DESCRIPTION Referring to FIG, 1, 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. In. this example, the monitor 12 is a fetal heartbeat monitor. The monitor 12 (discussed in detail below) has acoustic transducer (sensors) .1 6a4 6e that convert acoustic energy from the pregnant woman 14 into electrical energy. The transducers I 6a- 1 6 are coupled to the monitor 12, via conununication channels, 8a- I Sc, which can be wires connecting to the monitor 12 or wireless channels (radio fequency, optical and/or hikared). 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 1b monitors the pregnant woman's uterus to measure uterine contractions, The tmrnsducer 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 and status of the patient and fetus. The third transducer 16e 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 omni-directional but localized about the back of the fetus, Such localization is attributed - to preferred acoustic propagation to sites where the fetal back is against the maternal abdominal wall The acoustic propagation through the mamnal wal is omni directional but there is a point of maximum acoustic conduction, which is the point wCre the fetus' back is pressed against the uterine wall However, other positions can be used to attach the transducer 16c to the pregnant woman., in 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 iCasure 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 16e are deployed fior fetal detection and arrnged about the maximal fetal acoustic energy. This is a noise reduction technique that can be used in eases where it is difficult to sense the fetal heartbeat (e g, in the case of an overweight pregnant woman or underweight fetus) extra fetal sensors can be deployed to boost the strength of the fetal signal. Furthermore, 3 or more fetal sensors can be used to 14 WO 2007/130958 PCT/US2007/067906 triangulate the position of the fetal heart This localization information can be used by doctors and technicians during labor and delivery; Referring to FIG. 1,the monitor 12 includes a processor 30, e.g, a general purpose central processing unit (CPU) and/or a digital signal processor (DSPl1) to process signas front the patient. a memory 32 to execute programs, persistent, e, non-voiatile storage 34, and L1O interface(s) 36 all coupled via a bus 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 12 also processes signals from the transducer 14b that monitors for contractions in the pregnant womanr s uterus. Processing 50 provides a relatively clean detection of the fetal heartbeat by elinrinatig major sources of noise in the fetal heartbeat signal, cg. the relatively strong acoustie energy components contributed to the detected fetal heartbeat caused by the pregnant woman's heartbeat, I1 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 I,0 can also include other user interface devi ces, 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 HG. 3, the monitor 12 includes an interface 36 that interfaces the monitor 12 to the transducers 16a-16c, The interface 36 here is shown to include channels 36a-36c for transducers 16a-16c, respectively. Each channel 36a-3 6c in cihides a receiver 40 (if the monitor is a wireless version) or an analog signal interface (not show') to cables (not shown) from the transducer, if the monitor 12 is a wire-connected version. ln addition, the interIce 36 includes a low noise amplifier and a filter generally 42 to process analog signals frmn the transducers 16a-1 6c The amplifier 14 amplifies the signals and the filter filters the signals to preserve frequencies in the range of, e g., 0.05 to 100 lz 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 140 to 30 liz adn especially in a range f i8to 25 Hz (the rnge of maximai spectral power of the fetal heart signal). The maternal channel can be within the broad rangc above, hut most likely will in a range about 6 to 14 Hz and especially in a range of 8 to 12 Hz (the region of maximal power of the maternal heart signal), Whereas, the transducer 14b that senses the 15 WO 2007/130958 PCT/US2007/067906 maternal contractions need not have any ftering since it is a very long period g, a large impul se. Each amplifier 14 feeds the signal to an A/D converter 44 that digitizes the signal, at a sampling tequency at least greater than twice the highest frequency component in the channel. In otier im1plenentations, a single A/D converter and a inultiplexer can be used to process data from the channels (See FIG. 4). The digitized signals from each of the channels are transferred to tie bus interface device 46 that formats the digitized signals to place on the bus 38 (FIG. 2) to send to the memory 34 and/or processor 32 to be processed, R.efering to FIG. 4, an alternative arrangement fir the monitor 12 interfaces the monitor 12 to the transducers I 6a- 6c, A channel 36a6c is provided for each transducer 16a-i6c. Each channel 36a-36c 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 mnitor is a wire-connected version. In addition, the interfaces 36a to 36e include a low noise amplifier and a filter generally 42 to process analog signals from the transducers "6 and 16c and a low noise amplifier generally 42' to process analog signals rm the transducer 16b. The amplilier 14 amplifies the signals and the filter filters the signals to preserve frequencies in the ranges discussed above. Each amplifier/filter 42 and amplifIer 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 componentin the channel, according to control provided from the processor. The single A:D converter and nultiplexer 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/nux 44, whereas the DSP 45 processes output signals from the ADC/muax 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 firth, The monitor 10 can also include other user interface devices, eig, 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, eg, nonvolatile storage, and i/O interfaces) all coupled via buses (not shown) to the digital signal processor 45 and processor 48, WO 2007/130958 PCT/US2007/067906 Executed by DSP 45 is signa processing software 510 that processes signals from the transducers 16a and 16e 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 womaias uterus. This data are fed to the processor to 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 najor 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 pre gnaa woman 's heartbeat, In some embodiments, acoustic energy components from uterine contractions could also be filtered from the detected fetal heartbeat acoustic energy, Rt-eerrng to F1 5, pro essing o signals from. the transdueers is show-n. The signals from channels 36a, h3c are passed through digital band pass filters 1a, 51b to filter the signals in the range discussed above, e.g, 18 to 25 lm zfor the fetal channel and 8 to 12 iz-for the maternal channel The other ranges above could be used. The component of the pregnant voman's heartbeat that appears in the fetal channel is removed from the fetal signal in the difference block S1c. From the difference block, the signal is fed to a pitch track processor 52. The pitch track processor 52 uses pitch tracking and a principal component analysis to senate waveforms that can beused to determine heart rates, esg., in heart rate processor 55 and process the signal to provide an ECG from ECG processor 56, These signals can be displayed on display 58. The modulator 54 takes the output signal from the difference block 51d 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 d to provide an output signal that can be heard by humans. This signal can be converted to an analog representation and fed to Un audio amplifier, to be rendered onom a speaker 5, etc. Details of processing are discussed below, Referring to FIGS. 6A-6E through 8A-8C, collectively FIGS. 6-8, details of construction for an acotistic 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 1 6a to acquire the maternal heart. beat signal and transducer I6 Ob. the tcodnmomer(TOCO) transducer to detect maternal contractions, as father described below.
WO 2007/130958 PCT/US2007/067906 Transducer 1 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 61, in particular a double-sided adhesive, which in addition to providing for attachment of the transducer 16C to the epidermis also provides acoustic imnpedance matching between, the epidernis and a piezoelectric mmcibrane 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-,E, co llecti vely, FIG. 6, the acoustic transducer "button" 16c includes a base member 60. The base member 60, as depicted in FIG. CA, includes a frame arrangement 62 that supports bosses 64 to carry a circuit board (not shown) that supports signal preconditioning circuits, as discussed in Fi G 9. FIGE 6A depicts an aperture 66 in a bottom portion 60a of the base 60. A pol ynier membrane 68 covers a substantial portion of the aperture 66a 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 showMn), for example, are attached to thie electrodes of the polymer 68. Bosses are provided in the base 60 to elevate a circuit board above the plante Of the bottom of tile base 60 to provide clearance for wires, that couple to the electrodes on the polymer membrane 68. As shown in FIG. 613, 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, dcpendiing on manufacturing constraints other configurations such as connecting the PCB to the membrane via electrodes provided through the base may be preferred. in addition a iban 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 Tmajor surface that is contacted by the double-sided adhesive tape 61 on what will be the Outside of the base 60, as shown in FIG. 6C, and a second major surface that is within the transducer, The adhesive layer 61 is provided on the bottom of the base arnd over the outside surface of the polymer menibrane 68, In general, the adhesive vayer contacts tIe polymer ieibrane CS on. the outside, major surface; thus securing the polymer membrane 68 into the transducer. The adhesive 69 is provided as a double-sided adhesive medieaiarade tape of a 4,5 mil double coated polyester tape, coated on both sides with a hypoaliergeie, 18s WO 2007/130958 PCT/US2007/067906 pressure sensitive synthetic rubber based adhesive on a I ml transparent polyester carrier with a release hiner silicone coated 60 lb bleached Kraft paper. This tape is etylene oxide, gamma and autoclave process tolerant. One suitable product is Tape No. 9877 -rm 3M Corporation Minneapolis MN. Other adhesive tapes and adhesives could be used. In conventional approaches, as mentioned above an acoustic match is provided by a gel that is applied on the matemal abdomen. Typically, the operator covers a region of the abdomen with. the gel (a shppery, 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. 'IThe belt is unibersome and especially accurate (since often the sensor slips off of its target)I and it has to be removed prior to surgery or emergency procedures. In contrast the adhesive tape 61 secures the polymer membrane to the transducer 16a, 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, proNdes acoustic couplmg between the polymer 68 and the matermal abdomen, in some embodiments, material can he interposed between the tape and the polymer membrane for additional acoustic impedance matching. Hcre the tape 69 provides acoustic impedance matching, while securing the polymer 68 to the transducer 16e and also securng the transducer 16e to the abdomen of the patient As depicted in FIG 6D, a snap member 71 is disposed on an inner portion of the sidewall of the base member 60, to fiasten a. dome cap member 74 (FIGS. 7A-7) 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 number 60 from a side opposing the slot 69. Referring 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. 7G. The done cap 80 has a generally convex outer surface to increase the mechanical integrity of the transd acer ho using. 19 WO 2007/130958 PCT/US2007/067906 FIGS, ?C and 7D depict details of the snap receptacle member 84 to secure the dome 80 to the base 60. Other fastening arrangements are possible including gluing, screw fastening; wel ding and so forth, The base 60 and the dome 80 are comprised of a generly translucen material One type of material for the dome 80 and base 60 is ABS. especially medically approved ABS. ABS is a plastic, especially any of a class of plastics based on acryionirrile-btadiene~ styrene 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 pref erably 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 LED's can be used to indicate status and health of the transducer, as discussed below. The LED's could also be outside of or mouned into the base or dome the device. Referring to FIGS SA4C, the assembled transducer 16c is lustrated with the base member 60 secured in place to the dome cap 80, with the polymer membrane 68 exposed on the bottom with the adjacent cavity 66, Referring to FIGS 9A-9IB, collectively FIG. 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 68a68c, The membranes 68a-68C improve sensitivity and can be electrically coupled in series to increase the overall voltage produced from the patient or in parallel to increase the amount of charge and hence reduce the input impedance for the high impedance anmplfier. The Polymer membrane 68 or 68a-68c can be comprised of any suitable polymer material that exhibits piezoelectric properties, Certain polymer and copolymer materials such as polyvinyldene fluoride (PVDF) have long repeating chains of "C2 Cli" molecules that 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 trom Measurement Specialties Inc. Valley Forge PA as part No, SDTI.-028k, which is equivalent to DTI-028k whose properties are in the table below, 20 WO 2007/130958 PCT/US2007/067906 but without a protective urethane coating. This is a 028 micron thick polyiner 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 camping, crinps, eyelets, conductive epoxy or low temperature solders and so forth. Number A C 1 S electrode flm d ctrode thickness C at. DT 1-028K ,64 06) 484 (12) 1,63 (4l 119 0) 40 138 af Where. dimensions A-B are In mllimeters (mm). F is capacitance (nf nanofarads and where A and C are the width and length of the film, B and D are the width and length of the electrode and E is the thickness of the PVDF polymer. Other thickness, sizes and types of piezoe1ctric PVDF polymer could be used. In one niode of operation, mechanical energy in the forn of acoustic energy from the pregnant woman (detected fetal and maternal heartbeats or detected contractions) impinge upon "he combination of electrodes and sheet of material causirug 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 diffFernce 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 16a 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 Ii general, the precordimni is the external surface of the bodyv overlying the heart and stomach, typicallyinl the case of a pregnant woman, under the led breast of the patient. A tocodynamometer (TOCO) transducer 16b for measurement of maternal uterine contractions is also constructed in a similar manner. The tocodynamometer (TOCO) transducer 16b like the other transducers is a self-powered device, at least in wireless applications. The tocodynamoneter (TOCO) transducer I6b is a small, self-adhering device that detects contractions of the muscles of the pregnant woman's uterus by sensing tightening or the matenaI epid em- in the vicinity of the uterus, Transducer 16b is similar in construction to the transducers I6a and 16c, and is coupled to the monitor, via one of the WO 2007/130958 PCT/US2007/067906 input channels. The signal from. the transducer 16b is processed to provide a measure of the rate of contractions of the uterus. in an alternative embodiment, the TOCO transducer 16h is a conventional stnnn gauge whi0h does not require the acoustic equipment of the heart beat onnitor. Together, transducers 16a and 16c comprise a transducer system for capturing acoustic energy that can include the fetal heart signat and with the analysis described FIGS. 4 and 5 can produce an audible and acoustic signal of the fetal heart from which the fetal condition can, be ascertained. In 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, heart rate and rate of uterine contractions, The set of transducers 16a-I 6e provides minimnal di scomfort to the pregian t woman. complete transparency with regard to the currently employed delivery room fetal 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 colance with FCC regulations posing no risk (according to contemporary medical views) to the pregniiant woman, the infant, or any technicians and clinicians. One preferred. wireless technology employed is low power, Bluetooth' (Bluetooth@ SIG, Ine.) wireless techno ogy approved for medical applications, Referring to FIG, 10, circuitry 1 00 on the circuit board housed in the transducer 16e is shown. The circuitry 100 includes a high impedance amplifier 102 that interfaces to wires from ithe electrodes on the polymer membrane 68, as well as a battery 104 and a transmitter device 106 (or a analogy driver circuit (not shown) if the transducer I6e is coupled to the monitor 12 via wires. Also included is an antenna element 108, here a dipoie antenna internal to the transducer, An on-chip antenna device may alsoeued Other techniques could be used such as infrared or optical In 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 'ode 105, in operation, each transducer 16a-i6c when powered up would first be registered with the monitor 12, eg, a procedure that stores in the monitor 12 the uniue iden tiier of 22 WO 2007/130958 PCT/US2007/067906 the transducer that the monitor is wireless coupled to Each time the transducer sends data to the monitor, the traiisdier includes the transducer identifier, so that the monitor would be certain that it is processing data from the correct transducer.registered for that monitor. and not hon transducers regisv ith 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 oftwireless transducers, the three LEDS, one red, one yellw and one green, can be used to indicate the statuses of respectively. faiure." , of a battery, as shown or by failing to receive ant output signal fton 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 from the monitor indicating that it is registered with the monitor; and "working" by sensing the output the transmitter. Alternatively, the LEDs can sense outputs from the ainmplifier. Referring to PG,1(1 the high impedance amplifier 1t2 is used to interface with the polymer sheet 68, Since the polymer sheet 68 is capacitive in nature, a high input impedance amplifier is used to anplify the voltage potential generated across the polymer sheet prior to transmission (either wirelessly or with wires) to the monitor The ig Impedance amplifier 102 has components to set the operating point of the high imapedance amplifier 102. The high impedance amplifier 102 includes an operational amplifier 104 havig differential inputs one of which receives a portion of the output signal fed back to the inverting input -JNA of the amplifier 104. The signal from the sheet 68 is fed to the non-inverting Input +INA. Referring now to FIG. 12. details of the pitch processing block 52 are shown, From the difference block, 51d (FIG. 5) the signal is fed to pitch track analyzer 120, 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 tbr 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 coef icient) is assigned to each principal component of the data set. The pitch track analyzer 120 determines the pitch periods of the input wavebfn. The signal switch 122 routes the signal to the PCA generator 124 during an initial caihbration period. PCA generator 124 calculates the principal components for the initial 23 WO 2007/130958 PCT/US2007/067906 pitch period received. PCA Generator 124 sends the first, e.g.6 principal components for storage 130 and/or further processing, After the initial period, switch i22 routes the signal from the difference block to coefficient generator 126, which generates coefficients for each subsequent pitch period. instead of sending the principal components., only the coefficients are sent, thus reducing the number of bits. Swtch. 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 client are determined. lie pitch tracking analyzer 120 and the other components mention above are described in US. Patent Application Serial No. 10/624,139 fiIed July 21, 2003, published US-2004-01 02965-Al May 27, 2004 by Ezra J, Rapoport incorporated herein by reference in its entirety. The pitch track analyzer 120 determines the pitch periods of the input waetorn. The pitch track analzer20 dtmiins trends in the slight changes that modify a waveform across its pitch periods including quasi-periodic waveforms like heartbeat sigoda's. in order to analyze the changes that occur from one pitch period to the next, a wavecon- is divided into its pitch periods using pitch tracking process 53 (FIL 13). Referring now also to FIG 13 a pitch tracking process 121 receives i21 a an input waveform 75 (FG 14A) from difference block 51c to determine the pitch penods. 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, Hl'owever, each iteration of the pattern, or "pitch period" (e g, PP,) varies slightly from its adjacent pitch periods, e.g. PPo and Pl, 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 sarplinrg 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 121 b a standard vector (tIMe) length, V, Afier pitch tracking process 121 executes, the pitch tracking analyzer 120 chooses the vector length to be the average pitch period length pis 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 all vectors are a unifonn len gth and can be considered members of the same vector space. Thus, 21 WO 2007/130958 PCT/US2007/067906 vectors are returned where each vector has the same length and each vector includes a pitch period. Pitch tracking process 121 also designates 121c a buffer (time) length, BI, which serves as an "f fset and allows the vectors of those pitch periods that 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 at the end. This larger sample window allows for more accurate principal component calculations (discussed below). In the interest of storage reduction, the buffer length may be kept to between 10 and 20 sampling points (vector elcmnents) beyond thc length of the longest pitch period in the wavefo rmr At 8 kHz, a vector length that includes 120 sample points and an offset that includes 20 sampling units can provide optimuI results. Pitch 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 tracking process 121. determines 121 d an initial period length value by finding a real "cepstrum" of the first few pitch periods of the heartbeat signal to determine the frequency of the signal A cepstrun- is an anagram of the word "spectrum" and is a mathematical function that is the inverse Fourier transform of the logarithin of the power spectrum of a signal, The cepstrum method is a standard method for estimating the fundamental frequency (and therefore period length) of a signal with fluctuating pitch, A pitch period can begin at any point along a waveforn, 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 121 determines a single peak by taking the input wavefoRn, sampling the input waveforrm, taking the slope between each sample point and taking the point sampling point closest to zero, Pitch tracking process 121 searches several peaks within an xpectation age and takes the peak with the largest magnitude as the subsequent priiar pa 77. Pitch tracking process 121 adds 12 1f the prior pitch period to the primary peak, Pitch tracking process 121 determines 121g a second primary peak S location a maximum peak from a series of peaks 79 centered a time penod, P, (equal to the prior pitch period, Ps) from the first primary peak 77. The peak whose time duration from the prinary peak 77 is closest to tle time duration of the prior pitch period PP is determined to be the ending point 25 WO 2007/130958 PCT/US2007/067906 of that period (P) and the starting point of the next (PP), The second primary peak is determined by taalycng three peaks before or throe peaks after the prior pitch period tom the primary peak and designating the largest peak of those peaks as the second peak 82. Process 121 vectorizes 121i the pitch period. Pitch tracking processor 120 makes 12ij the second primary peak the first priniary peak of the next pitch period and recursively executes. eg, back to 121f, returning a set of vectors, That is, pitch tracking process 120 designates 121iJ the second primary peak as the first primary peak of the subsequent pitch period and reiterates (12 1 21j). Each set of vectors corresponds to a vectorized pitch period of the waveform, A pitch period is vectorized by sampling the waveftori over that period and assigning the i sample value to the > ceoordinate of a vector in Euclidean n-dimensional space denoed by 93 , where the index i runs from I to n, the number of samples per period. Each of these vectors is considered a point in the space N9", FI I 14B shows an illustrative sampled wavelorm of a pitch period The pitch period includes 82 sampling points (denoted by the dots Iying on the waveforn) and thus when the pitch period is vectorized, the pitch period can be represented asa single point in an 82 (or higher) -dimensional space, Thus, pitch tracking processor 120 identities the beginng 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 recursively, using the length of the prior period as an input to determine the duration of the next. Pitch tracking processor 120 can be stated as the following recursive function: The, ?unctionfidIP peo sd The function ftip') operates on pairs of consecutive peaks p and pfin a wavefon, recurring to Its previous vaiue (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 wavefori. This peak becomes the first peak in the next pitch period In. the notation used here, the letter p subscripted, respectivel, by "prev," "nw "next' and "7," denote the 26 WO 2007/130958 PCT/US2007/067906 previous, the current peak being exaniined, the next peak being examined, a the pe in the pitch period respectively, The value "s " denotes the time duration of the prior pitch period, and dpp ') denotes the duration between the peaks p and i B. Principal Component Analysis Principal comnponent analysis is a method of calculating an orthogonal basis for a given set or data points that defines a space in which any variations in the data arc completelyuncorrelated, PCA can be used as a compression technique to store pitch periods from the pitch tracking processor for detailed analysis. The symboL "9" is defined by a set of n coordinate axes each describing a diension or a potential for variation in 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 span Inultiple dimensions in 91* can be decomposed into its "principal components, "e., the set of eigen-axes that most naturally' describe the undcrling data, By implementing PCA, it is possible to effectively reduce the mu nber of dimensions, Th us, the total amount of information required to describe a data set is reduced by using a single axis to express several correlated variations. For example, FIG. 6A shows a graph of data points in 3-dimensions. The data in FIG. 6B are grouped together forming trends. F~i 613 shows the principal components of the data in FIG 6A. FIG, 6C shows the data redrawn in the space determined by the orthogonal principal components. There is no visible trend in the data in FG 6C as opposed to FIGS, 6A and 6.B I this example, the dinensionaliy 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 dirnersionality 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 thne amtt of data required to describe speech wavefnms. Referring to FIG 15, principal components process 124 detennines (1 52) the number of pitch periods generated from pitch tracking process 12.1 Principal components process 124 generates (154) a correlation matrix. The actual computation of the principal components of a wav eirn is a well-defined nathetnatical operation, and can be understood as follows, Given two vectors x and y, xyl WO 2007/130958 PCT/US2007/067906 is the square matrix obtained by multiplying x by the transpose of y. Each entry [xy ], is the product of the coordinatesi and y, Similarly, if X and Y arc maIrIces whose rows aTe the vectors x and y respectively, the square matix XY is a sum of matrices of the form [xy ;, XV can therefore be interpreted as an array of correlation values between the entries inI the sets of vectors arranged in X and Y. So when XV, XX'is an "auocorreation natrix in which each entry f[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 91' corresponding to the correlations between the vectors in X. The cigen-basis is the most natural basis in which to represent the data, because its orthogonality implies that coordinates along different axes are uncorrelated, and therefore represent variation of difitrent characteristics in the underying data. Principal components process 124 determines (156) the principal components from the eigenvalue associated with each eigenvector Each eigenvalie measures the relative importance of the different characteristics in the underlying data. Process 124 sorts (158) the cigenvectors in order of decreasing eigenvalue, in order to select the several most important eigen-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 pitch period onto the principal components. Intuitively any pitch period can be described by scaling each principal conponent axis by the corresponding coefficient for the given pitch period, followed by performing a sumnmation. of these scaled vectors. Mathenatically, 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, are the ith principal components, and the inner product etx is the scaling factor associated with the ith principal component. 28 WO 2007/130958 PCT/US2007/067906 Therefore, if any pich period canl be described simply by the aling and s umr.A1Aing..
4 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 all that is needed to reconstruct any pitch period and thus the principal components and coeicents are the compressed form of the original heartbeat signal. in order to reconstruct any pitch period. of n sampling points. n principal components are necessary. in the present case, the principal components are the cigenvectors of the matrix SS where the 1t row of the matrix S is the vectorized ith 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 97 percent accuracy. This is a general property of quasi-periodic data Thus tUe present method can be used to find patterns that underlie quasi-perioduc 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 nitch periods is greatly reduced. Because of the pattems that underlie the quasi-penodicity, 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 Dual ee Complex Wave/ce Tcnsfbrm, Ivan W, Seiesnick, et al, 1EEB Signal Processing Magazine 123 November 2005, which is incorporated herein in its entirety. The invention can be inplenwcted in digital electronic circuitry, or in computer hard ware., firmware, software, or in combinations thereof Apparatus of the invention can be implemented in a computer program product tangibly embodied in a machine-readable storage device for execution by a programmable processor; and method actions can be performed by a programmable processor executing a program of instructions to perform 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 includingat least one prograniabie 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 one output device. Each computer program can be implemented in a high-l evel. procedural or object oriented programming language, or in assembly or machine language if desired; and in any case 5 the language can be a compiled or interpreted language. 29 WO 2007/130958 PCT/US2007/067906 Suitable processors include, by way of example, both general and special purpose microprocessors. Generally, a Processor will receive instructions and data from a readonly memory and/Or a random access meonryl 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-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all fbnns of nonvolatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as intemal hard disks and removable disks; magneto-optical disks; and CD ROM disks. Any of the foregoing can be supplemented by; or incorporated in, ASJCs (application-specific integrated circuits} A number of embodiments of the invention have been described. Other embodiments are within the scope of the following claims, 30