RU2470581C1 - Method of registering patient's breathing and heartbeat rhythms and device for its realisation - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention relates to field of medicine. Method lies in irradiation of patient's body parts with the sum of two ultrasonic signals with differing frequencies. Current changes of phase shift between envelopes of transmitted and reflected signals, corresponding to vibrations of patient's body parts. As a result of processing of measurement results breathing and heartbeat rhythms are isolated in real time. Device for method realisation contains in transmitting part two generators, connected with two inlets of adder, whose outlet is connected to power amplifier with emitter. In receiving part device contains successively connected receiver, narrow-band amplifier and first detector, whose outlet is connected to second inlet of unit of phase shift measurement, as well as second detector, whose inlet is connected with outlet of transmitting part adder, and outlet is connected to first unit of phase shift measurement. Outlet of unit of phase shift measurement is connected with outlet of isolation of breathing and pulse constituents.

EFFECT: invention makes it possible to increase sensitivity and noise immunity in registration of breathing and heartbeat rhythms.

4 cl, 5 dwg

Description

The invention relates to medicine and can be used in medical practice for remote registration of breathing rhythms and cardiac activity of a patient in real time. Registration is intended for use in stationary conditions when the patient is in a calm state and the use of contact sensors is difficult, for example, when the patient is severely damaged due to any injury or burn, or when prolonged use of contact sensors can cause allergic reactions and irritation of the patient’s skin, and cause significant inconvenience.

Known methods for monitoring cardiac activity and the breathing process by recording the movements of tissues of the body area caused by the combined effects of respiratory and cardiac activities using electrodes or displacement sensors [1, 2, 3, 4].

The disadvantage of these methods is that they record the rhythms of breathing and heartbeat by the contact method, leaving the need to place electrodes on the patient's body or to fix special sensors, not allowing remote diagnostics.

Closest to the proposed method according to the technical essence and the totality of the signs of the sequence of actions is the "Method for registering an arterial pulse and respiratory rate and device for its implementation" [5], which remotely records the micromotion of a body area using a Doppler locator with a frequency of 10-100 GHz laying out the signal in quadrature components. Highlighting changes in the signal allows you to separate the respiratory wave from the pulse wave.

The disadvantage of this method is the extremely low sensitivity, which is expressed in a small Doppler frequency shift relative to the radiation frequency. To prove this, we take into account that the Doppler frequency shift is determined in accordance with the expression:

,

,

where Δf is the Doppler frequency shift;

f ₀ is the frequency of EHF radiation (10-100 GHz);

V is the speed of movement of the boundary of reflection, in this case it is the speed of movement of parts of the patient’s body;

C is the propagation velocity of EHF radiation (3 · 10 ⁸ m / s);

θ is the angle of incidence of the EHF beam.

Let us estimate the Doppler frequency shift for the case in which the displacements of body sections correspond to harmonic oscillations of the frequency F with amplitude l. Then the maximum speed is:

V = ωlcos (ωt).

является частотой пульса пациента, а l - амплитуда колебаний участков тела, связанная с сердечной деятельности. Выбрав предельно возможные значения F=3 Гц, а l=1 мм, можно подсчитать, что даже при столь высоком значении пульса максимальная скорость перемещения участков тела пациента не превышает 0,02 м/с. При этом дыхательная составляющая дает еще меньшие значения скоростей.In this case, the frequency

is the patient’s pulse rate, and l is the amplitude of fluctuations in body parts associated with cardiac activity. Having chosen the maximum possible values of F = 3 Hz, and l = 1 mm, it can be calculated that even with such a high pulse value, the maximum speed of movement of the patient’s body parts does not exceed 0.02 m / s. In this case, the respiratory component gives even lower values of speeds.

The relative displacement of the Doppler frequency can be calculated in accordance with the expression:

.

.

Substituting the above values of V and C into this expression, we obtain the maximum relative frequency change due to the Doppler shift:

Consequently, the Doppler frequency shift during pulse and respiration recording turns out to be much less than the intrinsic instability of any EHF generator, even on the basis of quartz stabilization. On the other hand, at EHF frequencies f ₀ of 10 GHz (10 ¹⁰ Hz), the Doppler shift does not exceed 1.3 Hz, which is clearly not enough to register a pulse at 3 Hz, because, based on Kotelnikov’s theorem, the Doppler frequency shift must be at least 6 Hz. Thus, the measurement of rhythms of heartbeat and respiration using EHF radiation, based on the Doppler effect, is practically unrealistic.

A device for recording pulse and respiration [7], based on the control of changes in the intensity of the received signal under the influence of respiratory and cardiac activities. The device contains an optical emitter and receiver, as well as filters for separating the respiratory and cardiac components of the received signal.

The disadvantages of this device are low noise immunity and a small percentage change in the intensity of the received signal under the influence of respiratory and cardiac activities.

A device is known for remote monitoring of respiration and heartbeat [6], based on radar location by an ultra-wideband signal of a patient and processing the received signal with the release of respiratory and cardiac activities.

The disadvantage of this device is the low noise immunity and low sensitivity, which required the use of low-noise amplifiers. In addition, this device is a source of serious electromagnetic interference to other medical electronic equipment due to its ultra-wide bandwidth, which is unacceptable in inpatient hospitals.

Closest to the claimed device is a device for recording arterial pulse and respiratory rate [5]. This device contains a transmitting generator connected to the emitter, a receiver of the reflected signal, a processing unit with a registrar. The last block contains a block for allocating a signal about the respiratory rate and a block for allocating a pulse signal.

The disadvantages of this device is the extremely low sensitivity of the registration method of the Doppler frequency shift when working with EHF radiation in accordance with the above proof.

The present invention is aimed at creating a reliable method for remote recording of rhythms of cardiac and respiratory activities, which has much greater sensitivity and noise immunity than analogues.

The solution to this problem is provided by the fact that in the method of recording breathing and heartbeats, irradiation of the patient’s body parts is performed by the sum of two ultrasonic signals with different frequencies f ₁ and f ₂ , the difference between which is associated with the fluctuation of the patient’s body parts by the expression:

where A is the amplitude of the oscillations of the patient’s body parts;

C is the propagation velocity of the radiation wave in the medium;

k is the coefficient establishing the sensitivity of registration.

After that, the current changes in the phase shift between the envelopes of the transmitted and reflected signals, corresponding to the vibrations of the patient’s body sections, are measured. As a result of processing the measurement results, breathing and heartbeats are distinguished. In this case, to measure the current change in the phase shift between the envelopes of the transmitted and reflected signals, integrate the envelope of the transmitted signal from the moment the envelope of the transmitted signal reaches the minimum until the envelopes of the transmitted and reflected signals are equal and continue to integrate, but now the envelope of the reflected signal until the minimum of the envelope of the reflected signal getting the total amount of S ₁ . Then integrate the envelope of the reflected signal until the new equality of the envelopes of the transmitted and reflected signals and continue to integrate the envelope of the transmitted signal until the next minimum envelope of the transmitted signal, obtaining the total sum S ₂ . Then determine the difference S ₁ -S ₂ corresponding to the current phase shift between the envelopes of the transmitted and reflected signals, freed from interference, and continue this process by tracking changes in the phase shift corresponding to the fluctuations of the patient’s body parts.

A device for recording rhythms of breathing and heartbeat, comprising in the transmitting part a series-connected generator, power amplifier and emitter, and in the receiving part, a series-connected receiver, narrow-band amplifier, a first detector and a respiratory and pulse component extraction unit, characterized in that it is equipped with a transmitting part a second generator of a different frequency and an adder of signals of both generators connected to the input of the power amplifier with an ultrasonic emitter. In the receiving part, it is equipped with a second adder signal detector and a phase shift measuring unit, the two inputs of which receive signals from both detectors and whose output is connected to the input of the respiratory and pulse components extraction unit. The phase shift measuring unit is equipped with two ADCs, two extremators and a voltage comparator, and the output of the first detector is connected to the inputs of the first ADC, the first extremator and the positive input of the voltage comparator, and the inputs of the second ADC, second extremator and the negative input of the comparator are connected to the output of the second detector, and it is also equipped with a digital integrator, to the two data inputs of which the corresponding outputs of both ADCs are connected, and the outputs of both extremators are respectively connected to three control inputs and a voltage comparator, while the output of the digital integrator is connected to the input of the allocation unit of the respiratory and pulse components.

The registration of fluctuations of the patient’s body parts in order to determine the rhythms of respiration and cardiac activity according to the invention is carried out using a device whose functional diagram is shown in FIG. A functional diagram of the phase shift measurement unit is shown in FIG. Timing diagrams explaining the operation of the generators and the adder are presented in figure 3. Timing diagrams explaining the phase shift calculation procedure are shown in FIG. 4.

The device contains harmonic oscillation generators 1 and 2, an adder 3, a power amplifier 4, an ultrasonic emitter 5, a first detector 6, a phase shift measuring unit 7, an ultrasonic receiver 8, a narrow-band amplifier 9, a second detector 10, a pulse and respiratory component extraction unit 17. The phase shift measuring unit 7 comprises a first extremator 11, a second extremator 12, a first voltage ADC 13, a second voltage ADC 14, a voltage comparator 15, a digital integrator 16.

The device operates as follows.

The generator 1 generates a signal corresponding to the expression:

x ₁ (t) = A ₁ sin (2π f ₁ · t),

where A ₁ and f ₁ - the amplitude and frequency of oscillations at the output of the first generator.

Generator 2 generates a signal corresponding to the expression:

x ₂ (t) = A ₂ sin (2π f ₂ · t)

where A ₁ and f ₂ - the amplitude and frequency of oscillations at the output of the second generator.

The output oscillations of the generators are summed using the adder 3. At the output of the adder with A ₁ = A ₂ = A, a beat signal of the form is generated (see Fig. 3):

which is amplified by a power amplifier 4 and supplied to an ultrasonic emitter 5, where it is converted into acoustic waves that irradiate parts of the body, such as the patient’s chest, and also enters the input of detector 6, where the envelope of the transmitted total signal is extracted. The signal corresponding to the envelope of the transmitted signal is supplied to the first input of the phase shift measuring unit 7.

The acoustic signal reflected from the patient is converted using an ultrasonic receiver 8 into electrical voltage. The output signal of the ultrasonic receiver is amplified and filtered from interference by a narrow-band (due to the small frequency difference f ₁ and f ₂ ) amplifier 9. The detector 10 detects the beat envelope of the reflected signal, which is fed to the second input of the phase shift measuring unit 7.

In the phase shift measuring unit 7, the extremators 11 and 12 highlight the moments of the minimum envelopes of the transmitted and reflected signals, respectively. An example circuit of the simplest extremator operating on the basis of a peak detector with a closed input at the base-emitter junction of the transistor is shown in FIG. The ADCs 13 and 14 convert the current voltages from the detectors 6 and 10 into an array of digital codes that are fed to the corresponding data inputs of the digital integrator 16. In addition, the signals from the detectors 6 and 10 are compared by a voltage comparator 15, the output of which is connected to the control input of the digital integrator 16. The outputs of extremators 11 and 12 are connected to two other control inputs of the digital integrator. Signals from extremators 11, 12 and comparator 15 control the integration process of the envelopes of the transmitted and reflected signals over time.

Digital integrator 16 works as follows (see figure 4). After the pulse arrives from the output of the extremator 11, the integration of ADC samples 13 begins. The process of integration of the samples of the ADC 13 continues until time t ₁ , when the unit potential appears at the output of the voltage comparator 15. After that, the samples of the ADC 14 are integrated until t ₂ , when from the extremator 12 an impulse arrives signaling the minimum envelope of the reflected signal. At time t ₂ , the accumulation of the first integral S ₁ ends.

Then begins the accumulation of the second integral. At time t ₂ , the integration of ADC samples 14 begins until t ₃ , when the potential zero is again established at the output of the voltage comparator 15. After the appearance of a logical zero at the output of the comparator 15, the ADC samples 13 are integrated until t ₄ , when the next pulse arrives from the extremator 7, signaling a new minimum of the envelope of the transmitted signal. At time t ₄ , the accumulation of the second integral S ₂ ends. After this, a difference code N = S ₁ -S ₂ is obtained, corresponding to the current phase shift between the envelopes of the transmitted and reflected signals, freed from interference. Then, the phase shift measurement process is repeated. With a phase shift of 90 °, the N code is zero (see Fig. 4a), with a phase shift> 90 °, the N code will be positive (see Fig. 4b), with a phase shift <90 °, the N code will be negative (see Fig. .4c). Such measurements continue from period to period of the envelope of the transmitted signal, thereby tracking phase shift changes corresponding to fluctuations in, for example, the patient’s chest. To organize the initial shift, approximately equal to 90 °, it is enough to introduce a frequency correction of one of the generators 1 or 2, which can be organized as a PLL.

From figure 3 and figure 4 it follows that for the unambiguous registration of the phase shift between the envelopes of the transmitted and reflected signals, the condition must be met:

where A is the amplitude of the oscillations of the irradiated portion of the patient's body; λ is the wavelength of the beats of frequencies f ₁ and f ₂ , which is in accordance with the expression

,

,

then

.

.

From here you can get the value of the frequency difference

,

,

выбрать так, чтобы коэффициент k был близок к 0.5, то максимальное изменение фазового сдвига будет достигать величин, близких 180°, т.е. чувствительность и соответственно помехозащищенность будут максимальными. При этом будет сохраняться однозначность измерений фазового сдвига.those. if the frequency difference

choose so that the coefficient k is close to 0.5, then the maximum change in the phase shift will reach values close to 180 °, i.e. sensitivity and therefore noise immunity will be maximum. In this case, the uniqueness of phase shift measurements will be preserved.

Code N from the output of the digital integrator 16 is fed to the block 17 for selecting the pulse and respiratory components, where there is a filtering and selection of signals corresponding to the rhythms of breathing and cardiac activity of the patient.

In the simplest case, the respiratory and pulse components separation unit 17 represents [6] a low-pass filter with a cut-off frequency of about 10 Hz, the output of which is connected to the inputs of a high-pass filter (HPF) and another low-pass filter (LPF), whose cut-off frequency is 0.6 Hz and 0.5 Hz, respectively. The first low-pass filter eliminates the signal from interference not related to the physiology of the patient. The high-pass filter extracts the pulse component from the remaining signal, and the second low-pass filter separates the respiratory component.

Literature

1. RF patent No. 2013996, A61B 5/08, 1994.

2. RF patent No. 2051616, A61B 5/024, 1996.

3. RF patent No. 2108059, A61B 5/024, 1998.

4. US patent US 5022402, 1991.

5. RF patent №2053706, АВВ 5/02, 1996.

6. RF patent No. 2392852, A61B 5/08, 2010.

7. E.M. Proshin, E.M. Grigoriev, S.G. Gurzhin, V.G. Kryakov, O.V. Kiryakov. Methods and technical tools for operational diagnostics, synchronization and biotechnological feedback in complex magnetotherapy // in the book: Complex magnetotherapy. - Moscow: Radio Engineering, 2010, p.155-157.

Claims (4)

1. The method of recording rhythms of the patient’s breathing and heartbeat, including remote irradiation of parts of the patient’s body with a signal and processing of the emitted and reflected signals to extract the respiratory and pulse components, characterized in that the irradiation is performed by the sum of two ultrasonic signals with different frequencies f ₁ and f ₂ , the difference between which are associated with fluctuations in the patient’s body parts by the expression:

,
where A is the amplitude of the oscillations of the patient’s body;
C is the propagation velocity of the radiation wave in the medium;
k is the coefficient establishing the sensitivity of the registration,
then measure the current changes in the phase shift between the envelopes of the transmitted and reflected signals, corresponding to the vibrations of the patient’s body part, and as a result of processing the measurement results, breathing and heartbeats are distinguished. 2. The method according to claim 1, characterized in that for measuring the current change in the phase shift between the envelopes of the transmitted and reflected signals, the envelope of the transmitted signal is integrated from the moment the minimum of the envelope of the transmitted signal appears until the envelopes of the transmitted and reflected signals are equal and continue to integrate, but now the envelope of the reflected signal to the minimum the appearance of the envelope of the reflected signal to obtain a total sum S ₁ is then integrated envelope of the return signal is equal to the time the new Twa envelopes of the transmitted and reflected signals and continue to integrate the envelope of the transmitted signal until the occurrence of the next minimum envelope of the transmitted signal to obtain a total sum S _2, after which the difference S ₁ -S _2, corresponding to the current phase shift between the envelopes of the transmitted and reflected signals and continue this a process by tracking phase shift changes reflecting fluctuations in a portion of a patient’s body. 3. A device for recording rhythms of respiration and heartbeat, containing in the transmitting part a series-connected generator, power amplifier and emitter, and in the receiving part, a series-connected receiver, narrow-band amplifier, a first detector and a respiratory and pulse component extraction unit, characterized in that the device is the transmitting part is equipped with a second generator of a different frequency and an adder of signals of both generators connected to the input of the power amplifier with an ultrasonic emitter, and in the receiving hour It is equipped with a second adder signal detector and a phase shift measuring unit, the two inputs of which receive signals from both detectors and whose output is connected to the input of the respiratory and pulse components extraction unit. 4. The device according to claim 3, characterized in that the phase shift measuring unit is equipped with two ADCs, two extremators, a voltage comparator, and the output of the first detector and the inputs of the second ADC, the second, are connected to the inputs of the first ADC, the first extremator and the positive input of the voltage comparator extremator and the negative input of the comparator are connected to the output of the second detector, and is also equipped with a digital integrator, to the two data inputs of which are connected the corresponding outputs of both ADCs, and with three control inputs, respectively o the outputs of both extremators and a voltage comparator are connected, while the output of the digital integrator is connected to the input of the respiratory and pulse components extraction unit.

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