The Dopler device for an assessment of cardiac activity of a fetus with digital block of a filtration of hums

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The Dopler device for an assessment of cardiac activity of a fetus with digital block of a filtration of hums

One of indicators of viability of a fetus is heartbeat. It is possible to determine various diseases and deviations in a child development by the frequency of heartbeat. Therefore it is necessary to watch heartbeat throughout pregnancy. In this work the device by which it is possible to determine a condition of a fetus by listening of its heartbeat is offered. The principle of operation of the device is based on a Doppler effect.

The diagnostic equipment intended for filing of parameters of activity of a fetus finds application generally in stationary medical institutions. Therefore work in the field of projection portable the fetal Dopler - devices of self-contained overseeing by heartbeat of a fetus that will allow future mother to trace self-contained a condition of the child, since twelfth week of pregnancy in comfortable conditions of the house is very actually.

To assess the heartbeat and control over the entire fetal heart rate using different methods:

1. Auscultation

2. Echocardiography

3. Fetal Electrocardiography

4. Cardiotocography

5. Fetal ultrasound examination

We suggest the device is intended for listening to heart and determination of fetal heart rate, which is based on the Doppler effect.

Basis of the Doppler methods is the Doppler effect which consists that an oscillation frequency of the sound waves radiated by a source (transmitter) of a sound, and the frequency of the same sound waves accepted by the sound receiver differ if the receiver and the transmitter move from each other (approach or removed). The same effect is observed if sound source signals after reflection by a moving reflector come to the receiver. This last case takes place at reflection of ultrasonic signals from moving biological structures (for example, blood elements) [1].

The block diagram of the Doppler device for determination of heart rate of a fetus with the intelligent block of processing of signals is given in fig.

The block diagram of the dopler device for an assessment of cardiac activity of a fetus with digital block of a filtration of hums: 1 - generator; 2-block test signal; 3 power amplifier, 4-balancing unit; 5 - sensor; the 6-radiating piezoelectric plate; the 7-accepting piezoelectric plate; 8 - amplifier of high frequencies; 9 - filter band-pass; 10 - digital adaptive filter; 11-amplitude detector; 12 - amplifier of low frequencies; 13-sound loudspeaker; 14 - switchboard of the mode; 15 microcontroller; 16 display

palpitation fetus pregnancy dopler

The device works as follows:

At turning on of the device the sensor 5 which consists of two pyezoplastin 6 and 7, is installed on the pregnant woman's stomach. The generator 1 constructed on the quartz resonator is necessary for creation of impulses which excite a piezoelectric plate 6. From the generator 1 the electric signal, reinforced in the power amplifier 3, through a balancing unit arrives on a piezoelectric plate 6, in it electric signals will be transformed to ultrasonic waves. Ultrasonic fluctuations through a forward abdominal wall of the pregnant woman get deep into her organism. These fluctuations extend in the woman's organism, being reflected from various acoustic discontinuities, in particular from fetus heart walls.

The signal reflected from a fetus heart wall arrives on a receiving piezoelectric plate 7 in which acoustic signals will be transformed to the electric.

Further the signal arrives on the amplifier of high frequencies 8 who is constructed on a chip of AD744 Analog Devices. The signal from the amplifier of high frequencies contains information not only on frequency heartbeat of a fetus, but also frequency of heartbeat of mother, and also various noise and hindrances, signals reflected from internals of mother. To allocate the signal corresponding to heartbeat of a fetus the filter band-pass 9, OP37 of Analog Devices firm constructed on a chip is used.

By means of the amplitude detector 11 constructed according to the two-stage scheme with the common feed-back the maximal peaks of a signal corresponding to heartbeat of a fetus are allocated. The BP is executed on chips of OP37 and AD744. With a BP the signal arrives on the amplifier of low frequencies 12 for strengthening of frequency of a signal to the range which is perceived by a human ear.

The reinforced signal arrives on the sound loudspeaker 13 by means of which it is possible to listen to heartbeat of a fetus.

Also the signal from the amplifier of low frequencies via the switchboard of the mode arrives on an entrance of the microcontroller 15 in which by means of the firmware timer there is a calculation of the square-wave pulses corresponding to heartbeat. The counted number of impulses is brought to the display 16 on which information on heart rate in beats per minute is displayed.

Accuracy of result at the developed device, mainly, will depend on accuracy of calculation of frequency the microcontroller. Testing function which allows checking a regularity of operation of the device is provided in the developed device.

For its realization the test signal is used:

The signal from the generator arrives on the block of a test signal 2. Further the signal via the switchboard of the mode arrives on an entrance of the microcontroller 14 in which similar to calculations of the cardiac contractions rate calculation of frequency of a test signal is made.

For noise elimination, the bodies of mother created by functioning the adaptive digital filter 10 is injected into the scheme.

The range of signal bears in itself information on the frequency of heartbeat of mother and a fetus, on a blood-groove in veins and arteries, information on functioning of organs of mother and a fetus, and also different network noises and noise which can be estimated as the useful signal. All noises are independent accidental processes which cannot always be removed by means of band pass filters. Therefore the digital adaptive filter of Winer which gives the chance to receive optimum filtering, in view of statistical characteristics of a signal and noise is entered into the device [2].

Distinctive feature of the developed device is the presence of unique filter that reduces interference to the desired signal. The microcontroller provides accurate heart rate calculation. The presence of unit test signal to verify correct operation. The presence in the Wiener filter eliminates noise and interference from the mother's heartbeat and the functioning of the various organs of the mother and fetus.

Advantages of the developed device:

· General availability and simplicity of carrying out research.

· Comfort of procedure: painlessness, lack of express preparation for carrying out research.

· Lack of an adverse effect of ultrasound on an organism of the woman and a fetus that allows to conduct multiple research during pregnancy.

· Research is conducted in real time and gives reliable information about heartbeat of a fetus.

· The developed device allows to listen to heartbeat of a fetus clearly.

References

1. Popechitelev E.P. i dr. Medicinskie pribory, apparaty, sistemy i kompleksy [Tekst]: Uchebnik / N.A. Kornelevskij, E.P. Popechitelev, S.P. Seregin; Kursk.gos.tehn.un-t. - Kursk: OAO «IPP «Kursk», 2009. - 986s. (Physical principles of ultrasound)

2. Rangajjan R.M. Analiz biomedicinskih signalov. Prakticheskij podhod./ Per.s angl. pod red. A.P. Nemirko. - M.:FIZMATLIT, 2007. - 440 s. (Filtering to eliminate artifacts)

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