CN106793996B - Method and device for determining fetal heart sounds by passive sensing and system for examining fetal heart function - Google Patents

Abstract

In the method according to the invention, a phonocardiographic signal obtained from the maternal abdominal wall by a passive acoustic sensor (10) is pre-filtered, amplified, digitized, digitally filtered by a programmable amplifier and filter unit (20), stored in an intermediate memory, and autocorrelation is performed by an autocorrelation unit (30) in a time window of predetermined size. The obtained signals as a result of the autocorrelation are fed to the input of a fuzzy expert system (40), wherein the local maxima of the signals, the temporal positions of the local maxima and the changes in the temporal positions of the local maxima are determined by the fuzzy expert system (40), and those determined are applied as input parameters or signals of the fuzzy expert system, classified into probability groups using fuzzy rule sets of decision logic stored in a knowledge base and biologically predictable data, and evaluated.

Description

Method and device for determining fetal heart sounds by passive sensing and system for examining fetal heart function

Technical Field

The present invention relates to a method for determining fetal heart sounds by passive sensing and a device for implementing the method, preferably the device may be used in a home environment and preferably the device may also be applied in telemedicine. The invention also relates to a system for examining the heart function of a fetus.

Background

It is known that a clearly interpretable measurement of fetal cardiac function can only be obtained by tests of longer duration (about 20 minutes); during such a duration, there is an opportunity to detect or timely notice phenomena associated with possible symptoms of the heart disease.

The most commonly used type of measurement today is ultrasound based on the doppler principle, which is an active method and thus involves continuous energy irradiation over a non-negligible period of time and is not suitable for tests carried out at home without supervision. The choice of passive methods suitable for checking the fetal heart function is very limited, mainly due to the problems associated with the physical fit and proximity to the body of the mother (pregnant woman), secondly due to the fact that the test requires a substantial expertise on the part of the person performing the test, and finally but equally important due to the excessive cost of such tests.

To circumvent the problems posed by ultrasound methods and to eliminate the need for expert personnel to be present during testing, phonocardiographic (phonocardiographic) methods have been developed, such as those disclosed in US6,551,251 and US6,749,573. These test methods employ multiple acoustic sensors, where the interpretable fetal heart sound signal is produced by processing the signals of the sensors individually and combining them. However, due to the problems associated with placing the sensor on the mother's abdomen and supporting the sensor against the skin, applying multiple sensors is cumbersome and results in a poor signal-to-noise ratio, thereby allowing measurements to be made with only limited accuracy and failing to meet the requirements of home and telemedicine applications.

The known solutions also include methods, devices and three chamber acoustic sensors according to EP 0850014 and US6,245,025, which allow sufficiently accurate fetal cardiac function examination and recording of cardiac function signals starting from a fetus of a certain age determined by various conditions (circumstance) and are also suitable for telemedicine applications. However, in more complex cases, there is a need to improve sensitivity and accuracy, and to be able to start performing phonocardiographic measurements at an early stage of pregnancy.

According to known solutions, it is intended to filter out the signals generated by the periodic heart beats from the detected noise-carrying (caden) signal by means of autocorrelation, such autocorrelation resulting in a reduction of the non-periodic signals of lower amplitude (substantially noise) but without allowing an increase in sensitivity and accuracy. In many schemes, error correction mathematical methods are applied to filter the sounds produced by the heartbeat from the noisy signal, but even then these methods do not improve the effective sensitivity and accuracy.

Disclosure of Invention

It is an object of the present invention to provide a phonocardiographic method and apparatus which provides improved sensitivity, reliability and accuracy in determining the sound of fetal heart function and thereby makes fetal heart function testing simpler, providing the possibility of conducting such testing at an earlier developmental stage.

Our further object is to provide a method that allows to obtain clearly interpretable results from tests carried out without supervision, at home or in telemedicine. In this connection, it is a further object of the invention to provide an improved acoustic sensor which also allows for an optimal detection of fetal heart sounds for subsequent evaluation in tests carried out without medical supervision, at home or in telemedicine.

The invention is based on the recognition that the autocorrelation, which reduces aperiodic noise, is not primarily applied to enhance the signal generated from periodic heart sounds, but rather for further noise filtering, so that the amplitude of the low-amplitude signal generated by autocorrelation is increased by further processing, and then the temporal position of the signal is determined with high accuracy.

It is a further insight of the present invention that such an improved sensor is suitable for achieving the object that the sensor, in addition to being easily operable by anyone, provides an optimal acoustic coupling to the skin of the mother's lower abdomen.

Thus, in the solution according to the invention, the fetal heart sound determination is determined by: pre-filtering, amplifying, digitizing and digitally filtering the phonocardiographic signal obtained from the mother's abdominal wall by the passive acoustic sensor,

stored in an intermediate memory, performs an autocorrelation in a time window of a predetermined size, then determines a local maximum of the obtained signal as a result of the autocorrelation, determines a temporal position of the local maximum and a variation in the temporal position of the local maximum,

and applying the results as input parameters or signals of a fuzzy expert system, classifying them into probability groups using fuzzy rule sets of decision logic stored in a knowledge base and biologically predictable data, and evaluating, storing the evaluated numerical results in input and output memories and control memories for further processing.

In a preferred way of implementing the method according to the invention, the values stored in the control memory are applied to adjust the gain of the amplifier and the parameters of the digital filter to achieve a maximum amplitude of the fetal heart rate signal and a minimum value of the disturbance signal.

In another preferred way of implementing the method according to the invention, a knowledge base and an inference system of a fuzzy expert system are applied and rules suitable for making inferences are selected on the basis of data stored in the knowledge base, and on the basis of the selected rules, the temporal distance (time difference) between the signals and thus the value of the Fetal Heart Rate (FHR) are determined by means of a fuzzy set.

In a preferred way of carrying out the method according to the invention, the digitized sound signal derived from the fetal heart sound is transformed to a higher frequency and the transformed sound is presented audibly.

In another preferred way of implementing the method according to the invention, the fetal heart rate signal previously stored in the memory is displayed, data, mainly personal and medical data, are assigned to the stored heart rate signal, and the data are stored locally or remotely for evaluation and archiving.

The apparatus constituting a further object of the invention is substantially characterized by:

the apparatus comprises an acoustic sensor adapted to be placed on the mother's abdominal wall and to convert acoustic signals of the fetal heart function into electrical signals, and further comprises:

a programmable amplifier and filter unit, comprising:

a programmable analog amplifier connected to the acoustic sensor, an analog filter connected to an output of the analog amplifier, an A/D converter connected to an output of the analog filter, a digital filter connected to an output of the A/D converter, and an intermediate memory connected to an output of the digital filter, an

An autocorrelation unit having a delay circuit, a multiplier circuit and an integrator circuit, wherein an input of the delay circuit and a first input of the multiplier circuit are interconnected and constitute an input of the autocorrelation unit and are connected to outputs of the programmable amplifier and filter unit, an output of the delay circuit is connected to a second input of the multiplier circuit and an output of the multiplier circuit is connected to an input of the integrator circuit, wherein an output of the autocorrelation unit is constituted by an output of the integrator, the apparatus further comprising:

a fuzzy expert system, the fuzzy expert system comprising: a parameter normalization unit adapted to receive a data signal and convert the received data signal into an input signal; a fuzzification unit connected to the output of the parameter normalization unit and adapted to convert the input signal into an input signal complying with the fuzzy rules; a fuzzy inference system connected to an output of the fuzzification unit and including decision logic corresponding to an inference process; a knowledge base unit connected to the fuzzy inference system via a bidirectional link and comprising a memory storing data sets defining boundary conditions and logic circuits defining decision rules; and a defuzzification unit connected to the output of the fuzzy inference system and adapted to convert the logical decisions into data signals, the input means of the fuzzy expert system being a parameter normalization unit connected to the output of the autocorrelation unit,

wherein the defuzzification unit of the fuzzy expert system comprises:

a first output providing time distance data of the Fetal Heart Rate (FHR) and a second output providing desired parameters of the digital filter, the first output being connected to an input of the input/output MEM3 memory and the second output being connected via the control MEM2 memory to a gain control input of the analog amplifier and a filter control input of the digital filter, wherein the outputs of the programmable amplifier and filter unit are connected to an acoustic transducer adapted to convert fetal heart sounds into audible signals and a modem providing bidirectional data traffic is connected to the input/output MEM3 memory.

The essence of the invention can be summarized as that the object is achieved by the following signal processing: such signal processing is implemented using programmable amplifier and filter units, autocorrelation units and fuzzy expert systems connected in series and optimized by controlling the amplification and filtering.

A preferred embodiment of the device comprises a microprocessor circuit comprising an input a/D converter, an a/D converter comprising a programmable amplifier and filter unit, a digital filter and an intermediate MEM1 memory, and further comprising an autocorrelation unit, a fuzzy expert system and a control MEM2 memory and an input/output MEM3 memory. Preferred embodiments are also contemplated in which the microprocessor is implemented and programmed as a microprocessor of a mobile phone, iPOD, or other computing device.

In another preferred embodiment of the device the input/output MEM3 memory comprises an external data input.

In another preferred embodiment of the apparatus, the acoustic sensor comprises: a case, an inner space of which is divided into an open first chamber, and a closed second chamber and a closed third chamber; a sound conduction opening provided in a partition wall between the first chamber and the second chamber; an electromechanical acoustic transducer, which is arranged in the third chamber, the sensor diaphragm of which is arranged in a wall between the second chamber and the third chamber, the first chamber having an edge adapted to be brought into abutment (fit against) against the mother's abdominal wall, wherein the first chamber is closed in its position in abutment against the mother's abdominal wall, and wherein a respective small-diameter pressure equalization opening to the outside air is arranged in the side wall of each of the first chamber and the third chamber.

The fetal heart function test system according to the invention is essentially characterized in that it comprises one or more fetal heart rate test devices according to the invention, a corresponding interface modem connected to the output of the fetal heart rate test device, a central computer adapted for medical evaluation and archiving, one or more computers adapted for use by the treating physician and/or a mobile phone capable of data communication and display, said units being interconnected via a data connection carrying a bi-directional data service over the internet.

Drawings

The essence of the invention is described in detail below with reference to the accompanying schematic drawings, in which:

fig. 1 shows a substantially undisturbed acoustic signal of a fetal heart sound;

FIG. 2 illustrates the main steps of the method according to the invention;

FIG. 3 is a block diagram of an apparatus according to the present invention;

FIG. 4 is a block diagram of a preferred embodiment of the apparatus according to FIG. 3, partially implemented with a microprocessor;

FIG. 5 shows a schematic cross-sectional view of a preferred embodiment of an acoustic sensor for use in the apparatus; and

fig. 6 is a possible arrangement of a system according to the invention.

Detailed Description

Fig. 1 shows a non-interfering acoustic (phonocardiographic) signal of the fetal heart sound. In this figure, the two characteristic signals S1 and S2 corresponding to the opening (S1) and the closing (S2) of the fetal heart valve can be easily seen; the instantaneous heart rate (instantaneous FHR) is determined based on the time difference between subsequent signals S1 or S2.

The main steps of the method according to the invention are illustrated in fig. 2. During the method, the phonocardiographic signal obtained from the mother's abdominal wall by means of a passive sensor is amplified, digitized, filtered and subjected to an autocorrelation process applying a time window of predetermined size, and the obtained signal sequence as a result of the autocorrelation is processed by a fuzzy expert system.

During processing, the obtained signals as a result of the autocorrelation, as input parameters of the fuzzy expert system, are classified into probability groups using a rule set of decision logic stored in a knowledge base (the rule set comprising biologically expected signal ranges and corresponding occurrence probabilities), and the signals are then evaluated. The local maxima of the obtained signal, the temporal position of the local maxima and the variation of the temporal position of the local maxima as a result of the processing are determined. The amplification gain is adjusted to achieve the optimal gain by blurring the first output signal of the expert system, the second output signal of the fuzzy expert system is applied to adjust the filter parameters such that minimal noise is achieved, and the third output signal comprising the frequency of the fetal heart sounds is stored for further evaluation and processing.

Fig. 3 shows a block diagram of a device according to the invention.

The device has an acoustic sensor 10 and a programmable amplifier and filter unit 20, wherein an output of the acoustic sensor 10 is connected to an input of the programmable amplifier and filter unit 20. Programmable amplifier and filter unit 20 has a controllable gain analog amplifier 22, an analog filter 23, an a/D converter 24, a programmable digital filter 25 and an intermediate MEM1 memory 26, all connected in series. Analog amplifier 22 and digital filter 25 have respective control inputs adapted to adjust the gain of analog amplifier 22 and one or more parameters of programmable digital filter 25, such as frequency range, slope, damping, etc.

The apparatus further comprises an autocorrelation unit 30 having a delay circuit 31, a multiplier circuit 33 and an integrator 35. The output of the programmable amplifier and filter unit 20 is constituted by the output of an intermediate MEM1 memory 26, the output of which intermediate MEM1 memory is connected on the one hand to the input of the delay circuit 31 and on the other hand to a first input of a multiplier circuit 33, wherein the output of the delay circuit 31 is connected to a second input of the multiplier circuit 33. An output of multiplier circuit 33 is connected to an input of integrator 35, wherein an output of integrator 35 is connected to an input of a fuzzy expert system 40.

The input unit of the fuzzy expert system 40 is a parameter normalization unit 41, the output of which is connected to the input of a fuzzification unit 43, the output of the fuzzification unit 43 being connected to a first input of a fuzzy inference system 45. The fuzzy expert system 40 further comprises a knowledge base module 47 which is connected to the fuzzy inference system 45 via a connection providing a two-way data transmission.

An output of the fuzzy inference system 45 is connected to a defuzzification interface 49, wherein one output of the defuzzification interface 49 is connected to respective control inputs of the analog amplifier 22 and the digital filter 25 of the programmable amplifier and filter unit 20 via a control memory 60, and another output of the defuzzification interface is connected to an input of an input/output MEM3 memory 50. The memory 50 has an external data input 90 and the docking modem 80 is connected to the memory 50.

An acoustic presentation unit 70 adapted to convert fetal heart sounds into audible signals is also connected to the output of the programmable amplifier and filter unit 20.

The apparatus operates by: fetal heart sounds detected acoustically at the mother's abdominal wall are converted to electrical signals by the acoustic sensor 10, the converted signals are amplified to a desired level in a controlled manner by an analog amplifier 22, and an analog filter 23 is applied to filter out the higher frequency components from the detected signals as they fall outside the frequency range of the fetal heart sound signals. The amplified and filtered signal is converted to a digital signal by a/D converter 24 and the digitized signal is further filtered using programmable digital filter 25 to filter out components that fall outside the frequency range of the useful signal while adjusting the signal that falls within the useful range to an optimal amplitude taking into account the age of the fetus, the mother's size and the location of the fetus. The filtering reduces low frequency components, maternal heart sounds and other interfering signals on the one hand, and also reduces the higher frequency components of external interference on the other hand. The amplifier gain and filtering parameters are programmed to obtain a maximum fetal heart sound signal and a minimum interference signal. The digital signal sequence thus obtained is stored in the intermediate MEM1 memory 26.

The correlation function is generated by the autocorrelation unit 30 according to the following equation:

wherein

t represents time

τ denotes delay time (time distance between clock signal pulses)

R (tau) represents an autocorrelation function

v (t) represents primitive functions

v (t-tau) represents the primitive function of the delay

The delay time of the delay circuit 31 is chosen to be so small that the resolution of the applied fetal heart sound signal may produce an autocorrelation signal with sufficient accuracy.

As a result of the autocorrelation, periodic signals maintain their periodicity, while non-periodic signals (i.e., most of the noise) are significantly reduced in amplitude.

The intermediate MEM1 memory 26 of the programmable amplifier and filter unit 20 is connected to the input of the autocorrelation unit 30 and is also connected to the input of the input/output MEM3 memory 50 and to the acoustic presentation unit 70 adapted to present the fetal heart sounds.

The length and size of the autocorrelation function corresponds to the smallest bio-probable heart rate and the sampled value, i.e. in our case the fetal heart sound signal containing at least four fetal heartbeats. Applying a parameter normalization unit 41 of the fuzzy expert system 40, performing a parameter normalization on the output signal obtained from the autocorrelation, comprising the steps of:

-detecting peaks in the signal (detecting at least four amplitude maxima),

-sorting the detected peaks by their amplitude,

-selecting at least four signals having the largest amplitude.

The selected signal most likely constitutes a fetal cardiac signal sequence. Since the heart sound signal may be masked by noise, it has to be tested whether the detected peak (maximum) is really a characteristic of the heart function. For example, it may happen that a fetal heart sound signal cannot be found due to noise, but the fetal heart sound signal sequence may still be utilized to detect or determine the fetal heart sound signal. In these cases, the measured signal sequence does not have to be discarded, but other acceptable values should be used to determine the position of the fetal heart sound signal.

The signal resulting from this parameter normalization operation is fed to the input of the fuzzification unit 43.

In the process of blurring, the information content of the signal is converted into a blurred input signal according to a blurring rule.

By blurring the input signals and based on inference rules and data (such as physiological rules and previous measurement data) defined in a fuzzy language and stored in the knowledge base module 47, the fuzzy inference system 45 is applied to make inferences by fuzzy and logical operations, during which the probabilities of the respective signals having the maximum value falling within a given set of processable signals are determined and the obtained results are applied to specify a new strategy to be stored in the knowledge base module 47, in which process the fuzzy inference rules and inference data are modified in correspondence with the results.

The defuzzification performed with the defuzzification interface 49 comprises converting the output signal of the inference system into a numerical signal, on the basis of which it can be determined whether a useful cardiac sound signal has been found. Once the majority of the useful cardiac signals have been found, the values (time positions of peak amplitudes) as a result of the defuzzification are stored in the input/output MEM3 memory 50. If the fetal heart sound signals (and their recurrence) are not found based on the evaluation provided by the fuzzy inference system, then the measurement is considered to be unintelligible and the search is restarted.

During the evaluation, a second output signal is generated by the fuzzy inference system 45 that is proportional to the amplitude of the fetal heart sound signal and proportional to the level of noise caused by other signals that are measurably considered to be interfering signals. This second signal is stored in the control MEM2 memory 60 and it is also used to control the amplifier 22 and the filter 25, in a manner to act as a control loop that adjusts the gain of the amplifier to achieve the maximum possible value of the fetal heart sound signal and sets the filter parameters (bandwidth, slope) so that the lowest possible noise level is obtained.

The device may be connected to an external system via a modem 80 connected to the input/output MEM3 memory 50, while other data (e.g. data describing the movement of the fetus) may be input simultaneously with the measurement via the external data input 90.

Fig. 4 illustrates a block diagram of an embodiment of the device according to fig. 3, for example implemented in part with a microprocessor. Alternatively, the microprocessor may be implemented as a mobile phone, e.g. as a so-called smart phone capable of data communication and display. The architecture of the microprocessor includes programmable implementations of the components that provide a/D conversion, programmable digital filtering, intermediate data storage, autocorrelation and fuzzy expert systems, as well as any such circuit components and programming capabilities to write data to and retrieve data from the memory unit and connection to the modem.

The device has an acoustic sensor 10 to which an amplifier 22 of a programmable amplifier and filter unit 20 and a filter 23 in series with the amplifier are connected. The output of the filter 23 is connected to the input of the a/D converter of the microprocessor.

The microprocessor also comprises a digital filter, a programmable unit adapted to perform the autocorrelation and a module of the fuzzy expert system, as well as an intermediate memory and a control memory and a memory adapted to store the measurement results and other data. Other data related to the measurements may be input to the memory through an external data input 90, and the microprocessor may interface with the data service system through modem 80. An acoustic display unit 70 is also connected to the microprocessor.

Fig. 5 shows a cross-sectional view of a schematic structural arrangement of the acoustic sensor 10. This configuration has maximum sensitivity in the frequency range of fetal heart sounds. The acoustic sensor 10 has a housing 11, the inner space of which is divided into a first chamber 13, a second chamber 16 and a third chamber 19. The chambers 13 and 16 are connected by means of a sound-conducting opening 14 provided in the partition wall between them. On its side opposite the sound conduction opening 14, the chamber 13 is open, while the chamber 13 has a rigid side wall in which the rim 12 is formed. During use, the edge 12 of the chamber 13 bears against the mother's abdominal wall, the chamber 13 being closed by the skin surface enclosed by the edge 12. The acoustic sensor 10 is placed in a biased (pre-loaded) state on the mother's abdominal wall, this pressure being generated by the flexible band and whereby the enclosed portion of the skin surface acts as a diaphragm. The external configuration of chamber 13 and the internal configuration of chamber 16 and the acoustic coupling between the two chambers together provide acoustic sensor 10 with desired frequency characteristics.

The electromechanical acoustic transducer 17 is arranged in a chamber 19, wherein the sensor diaphragm is arranged in a wall of the chamber 16 opposite the sound conduction opening 14. The chamber 16 has rigid side walls. A proper acoustic coupling between the maternal abdominal wall and the electromechanical acoustic transducer 17 is ensured by the volume of the chambers 13 and 16 and the dimensions of the sound conduction opening 14.

Respective small-diameter pressure equalization openings 15, 18 to the outside air are provided in the side walls of the chamber 13 and the chamber 19. These openings are adapted to reduce the damping effect of air masses (air mass) brought about by the vibrations of the enclosed skin surface during movement. At the same time, the opening 15 also acts as a high-pass filter adapted to attenuate the maternal heart sound. The opening 18 is adapted to reduce the effect of air pockets formed behind the electromechanical acoustic transducer 17 and to provide protection against background noise by compensation.

Thus, the acoustic sensor 10 translates out and provides a relative acoustic pre-filtered signal for further processing.

The configuration of a conceivable system for examining the heart function of a fetus is shown in fig. 6. The system allows performing fetal cardiac sound examinations at home primarily with the device 100 for the physician to verify the measurements and to store and archive measurement data and other information. The system comprises one or more devices 100, a docking modem 80 for each device 100, and a central computer 105 adapted for evaluation and archiving, and one or more computers 107 adapted for use by the treating physician and/or a mobile phone 109 capable of data communication and display, the aforementioned units being interconnected by the internet via a data connection carrying a two-way data service. When the system is in use, the results measured by the device 100 are transmitted via the modem 80 to a medical evaluation and archiving center where the data is evaluated, stored and archived. Equipped with an internet connection, the treating physician can also perform measurement evaluations using his/her own computer 107 or mobile phone 109 and send the information to mom and central computer. Thus, detection (measurement), display and measurement evaluation can be separated from each other in time and space.

The most important advantages of the method according to the invention, the device implementing it and the system implemented applying it are that it allows to examine and evaluate the fetal heart sounds at an earlier stage of pregnancy (before the last three months) compared to the known devices comprising acoustic sensors and, thanks to the proper configuration of the sensors and to the signal processing scheme provided by the series connected autocorrelation unit and fuzzy expert system, it allows a more accurate and more sensitive monitoring of the fetal heart sounds compared to the known devices. Another advantage associated with this is that it enables testing to be conducted without medical supervision, at home or in telemedicine.

Another advantage of the method and apparatus according to the invention is that in addition to measuring the fetal heart rate, symptoms related to other heart conditions can be detected.

List of reference numerals

10 sound sensor

11 casing

12 edge

13 (first) chamber

14 Sound conduction opening (connecting/coupling sound conduction opening)

15 opening (pressure equalization hole for attenuation)

16 chamber (second)

17 electromechanical acoustic transducer (Acoustic sensor)

18-opening (equalizing) pressure equalizing hole

19 Chamber (third), Balancing

20 programmable amplifier and filter unit

22 Amplifier (analog, adjustable gain)

23 Filter (simulation)

24A/D converter

25 Filter (programmable digital)

26 memory (middle MEM1)

30 autocorrelation unit

31 delay circuit

33 multiplier circuit

35 integrator

40 fuzzy expert system (logic)

41 parameter normalization unit

43 fuzzification unit

45 fuzzy inference system (logic)

47 knowledge base module

49 defuzzification interface (Module)

50 memory (input/output MEM3)

60 memory (control MEM2)

70 sound display unit

80 modem

90 external data input

100 device

105 Central computer (medical evaluation and filing)

107 computer (for treating doctor)

109 mobile phone (for treating doctor)

Claims (4)

1. An apparatus comprising an acoustic sensor (10) adapted to be placed on the mother's abdominal wall and adapted to convert acoustic signals of the fetal heart function into electrical signals, a programmable amplifier and filter unit (20) and an autocorrelation unit (30), the programmable amplifier and filter unit comprising:

a programmable analog amplifier (22) connected to the acoustic sensor (10), an analog filter (23) connected to the output of the programmable analog amplifier (22), an A/D converter (24) connected to the output of the analog filter (23), a digital filter (25) connected to the output of the A/D converter (24), and an intermediate memory (26) connected to the output of the digital filter (25), and

-the autocorrelation unit having a delay circuit (31), a multiplier circuit (33) and an integrator (35), wherein one of the inputs of the multiplier circuit (33) is interconnected with the input of the delay circuit (31) and connected to the output of the programmable amplifier and filter unit (20), -the output of the delay circuit (31) is connected to the other input of the multiplier circuit (33) and-the output of the multiplier circuit (33) is connected to the input of the integrator (35), -wherein the output of the autocorrelation unit (30) is constituted by the output of the integrator (35), the apparatus further comprising:

a fuzzy expert system (40) connected to the output of the autocorrelation unit, a parameter normalization unit (41) being an input unit of the fuzzy expert system (40), an output of the parameter normalization unit (41) being connected to an input of a fuzzification unit (43), an output of the fuzzification unit (43) being connected to an input of a fuzzy inference system (45), a knowledge base module (47) being connected to the fuzzy inference system (45) via a bidirectional connection, wherein a set of databases and rules are stored in the knowledge base module (47), an output of the fuzzy inference system (45) being connected to an input of a defuzzification interface (49), wherein an output of the fuzzy expert system (40) is constituted by an output of the defuzzification interface (49),

a first output of the defuzzification interface (49) is connected to an input of an input and output memory (50) storing fetal heart sound data, a second output of the defuzzification interface (49) is connected to a control memory (60) storing data for gain and filter control, and

an output of the control memory (60) is connected to a gain control input of the programmable analog amplifier (22) and to a filter programming input of the digital filter (25),

a modem (80) is connected to the input and output memory (50) and the input and output memory (50) is provided with an external data input (90), an

An output of the programmable amplifier and filter unit (20) is connected to another input of the input and output memory (50) and to an input of an acoustic presentation unit (70) adapted for audible presentation of fetal heart sounds.

2. The apparatus of claim 1,

-having a microprocessor circuit equipped with an input a/D converter, said circuit comprising said a/D converter (24) of said programmable amplifier and filter unit (20), said digital filter (25) and said intermediate memory (26), and further comprising said autocorrelation unit (30), said fuzzy expert system (40) and said control memory (60) and said input and output memory (50).

3. The apparatus according to claim 1 or 2,

the acoustic sensor (10) comprises: a housing (11) whose interior space is divided into an open first chamber (13) and into a closed second chamber (16) and a closed third chamber (19); a sound conduction opening (14) provided in a partition wall between the first chamber (13) and the second chamber (16); an electromechanical acoustic transducer (17) arranged in the third chamber (19), a sensor diaphragm of the electromechanical acoustic transducer (17) being arranged in a wall between the second chamber (16) and the third chamber (19), the first chamber (13) having an edge (12) adapted to abut against an abdominal wall of a mother, wherein the first chamber (13) is closed in its position abutting against the abdominal wall of the mother, and wherein a respective small diameter pressure equalization opening (15, 18) to external air is arranged in a side wall of each of the first chamber (13) and the third chamber (19).

4. System for examining the heart function of a fetus, the examination being carried out with a device according to any one of claims 1 to 3,

comprising one or more devices (100) according to any one of claims 1 to 3, a modem (80) connected to the output of the devices, a central computer (105) adapted for medical evaluation and archiving, and one or more computers (107) adapted for use by a treating physician and/or a mobile phone (109) capable of data communication and display, the one or more devices (100), the modem (80), the central computer (105), the one or more computers (107) and/or the mobile phone (109) being interconnected by the internet via a data connection carrying a two-way data service.

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