Device to select the beginning of the cardiac cycle

 

The invention relates to medicine, in particular to electrocardiography, and can be used to determine the start of the next cardiac cycle, coinciding with the beginning of P-wave, the analysis of low-amplitude potentials electrocardiogram (EX), temporal parameters EX and analysis of heart rate variability executed as hardware and software. The device comprises a filter unit sample, unit of comparison, the first circuit And the pulse counter, a second circuit, And first and second source thresholds and the source of timing pulses, the unit forming the differences of the second order and the trigger with the appropriate connections between them. The device provides improved reliability allocation start of each cardiac cycle, coinciding with the beginning of P-wave, regardless of possible deviations from normal parameters cardiomegaly drift and contour. 3 Il.

The invention relates to medicine, in particular to electrocardiography, and can be used to determine the start of the next cardiac cycle, coinciding with the beginning of P-wave, the analysis of low-amplitude potentials electrocardiogram (EX), remanifesting.

The most common in the present device to select the beginning of the cardiac cycle based on the detection of the QRS complex (the allocation of R-R intervals).

A device for separation of R-R intervals [1], contains the filter, peak detector, the driver of the threshold comparison, the comparator. This device has several disadvantages:

- R-prong may have a negative polarity, which will lead to the skipping of a QRS-complex;

- ECG split the R-wave reliability allocation the beginning of the cardiac cycle is reduced.

Closest to the proposed device (prototype) is a device [2], based on selection of the starting point of the cardiac cycle in the interval TR of electrocardiograma that makes the device insensitive to various changes in the shape of teeth of the FORMER and increases the reliability of the selection to the beginning of the cardiac cycle. However, this device has the following disadvantages:

- changing the heart rate, the position of the start point of the cardiac cycle relative to the beginning of elements EX, following this point, is changed, which makes it difficult to synchronize individual cardiocycle between a required, for example, in the study of late potentials fibrillation or late potentials as the AI, caused by the action of the FORMER low-frequency additive noise (polarization electrodes, respiratory wave, artifacts, and so on) reduces the reliability of the selection to the beginning of the cardiac cycle, because it does not exclude the situation when the signal amplitude representing a mixture of the FORMER and additive noise, can come on the interval TR for threshold levels, in defiance of the correct allocation of the beginning of the next cardiac cycle.

Attempt to remove low-frequency additive noise using the high pass filter will not work, because the cutoff frequency of this filter must have a small value (0.05 Hz in accordance with the standards for electrocardiographs), and the effect of artifacts leads to the transition process, which lasts the longer, the lower the cutoff frequency of the filter, during the transition process reliability allocation QRS-complex is reduced.

The proposed device allows you to eliminate the mentioned disadvantages and to provide a reliable determination of the beginning of the next cardiac cycle, coinciding with the beginning of P-wave, in terms of action on the EX additive noise.

The essence of the proposed method consists in the following. In the device containing the filter, the inlet of which is the input of the block sampling, generation of the rich, the output of the filter connected to the first input of the block sampling, to the second input of the latter is connected to the first generator output control pulses, the output of block sampling is connected to the first block of the input of the comparison, the second input unit of comparison is connected to the output of the first source threshold level, and a third input from the output of the second source threshold level, the output of the Comparer is connected to the input of the zero pulse counter and to the first input of the first circuit And the second input of which is connected to the second generator output control pulses, the output of the first circuit And connected to the counting input of the counter pulses, the bit outputs of which are connected to corresponding inputs of the second circuit And, put the block of formation of the difference of the second order and the trigger. The input processing unit differences of the second order is connected to the output of the sample rate and the output to the first input of the comparison, the output of the Comparer is connected to the input of a zero trigger input setup unit trigger is connected to the output of the second circuit And the trigger output is an output device. Block comparison is made on the basis of two Comparators and scheme and whose connections between them are described in the prototype [2].

In Fig.1 shows the structural diagram of the device to select the beginning of the AC is of geocycle contains the filter 1, block sample 2, the generator 3 control pulse shaping unit 4 differences of the second order, the block comparison 5, the first 6 and second 7 sources threshold level, the first 8 and second 9 scheme And pulse counter 10, the trigger 11.

The input of the filter 1 is the input device, the output of filter 1 is connected to the first (information) input block sample 2, the second input (the Manager) which is connected to the first output of the generator 3 control pulses. The output of sample 2 is connected to the input of the shaping unit 4 differences of the second order, the output of which is connected to the first input of the block comparison 5. The second and third inputs of the block comparison 5 are connected respectively to the outputs of the first 6 and second 7 source threshold levels. The output of the Comparer 5 is connected to the inputs of zero (R) pulse counter 10 and the trigger 11 and to the first input of the first circuit And 8, the second input of which is connected to the second output of the generator 3 control pulses. The output of the first circuit And 8 is connected to the counting input (S) of the pulse counter 10. Bit outputs of the pulse counter 10 is connected to the corresponding inputs of the second circuit And 9. The output of the circuit And 9 connected to the inlet of unit (S) of the trigger 11, the output of which is sokochastotnoy and network interference (signal "EX+additive interference" in Fig.2) is fed to the first (information) input block sample 2. On the second (control) input of this block receives control pulses. The repetition rate of these pulses determines the sampling frequency of the input signal (for electrocardiographs adopted a sampling rate of 200 or 500 counts/s In Fig.2 and 3 shows the timing chart when the sampling rate of 200 samples/s). The output of block sampling 2 mixture of cardiomegaly and additive noise is represented by discrete samples at the input of the shaping unit 4 differences of the second order. Forming a difference of the second order can be implemented as discrete samples of a continuous signal, for example, schema-based sample-and-hold and operational amplifiers, and digital signals, for example, based on the microcontroller type PIC16F7X with the input of analog-to-digital Converter that allows converting digital samples to a digital signal. In Fig.2 shows the signal at the output of the block forming the differences of the second order, the implemented schema-based sample-and-hold and operational amplifiers. The amplitude of this signal is compared in the unit of comparison 5 with two threshold levels, one of which is greater than zero (+U in Fig.2), and the second is less than zero (IPA Comparer 5 (signal Lips. 0" in Fig.3) is formed by a permission signal (for example, a high signal), otherwise a signal is generated prohibition (for example, a low-level signal). The low level signal from the output of the Comparer 5, when the inputs are zero (R) of the counter 10 and the trigger 11, sets them in the initial zero state whenever the signal amplitude difference of the second order will exceed threshold levels. When the signal amplitude difference of the second order is between the threshold levels at the output of the Comparer 5 is the enable signal of high level is supplied to the first circuit input And 8 and permit the passage at its output and then to the counting input (S) count 10 pulses from the second output of the generator 3 control pulses. These impulses (signals "Account" in Fig.3) are counter 10. The respective bit outputs of the counter 10 is connected to the input schema And 9. In Fig.3 as an example, output signals of the six-digit binary counter (the signals of the Outputs of the counter”). The input schema And 9 are connected to the outputs of the counter 10 so that the signal at the output of this circuit (the signal of the Mouth. 1" in Fig.3) appeared only at the moment of time when the counter count for certain what's the repetition frequency of clock pulses output from the generator 3 (i.e., the sampling frequency) and duration of interval PQ, ST and TR so that it could be achieved by counter 10 only on the interval TR. Leading edge of the pulse at the output of the circuit And 9 being set in the state “1” of the trigger 11 (signal "O" in Fig.3). The return of the trigger 11 in the state “0” (signal "O" in Fig.3) will occur only at the time when the next reference to the difference of the second order will exceed the threshold level at the output of the Comparer 5 you receive a low level signal (signal "Mouth. 0" in Fig.3), and this time corresponds accurately to the sampling period to the beginning of the R-wave of the next cardiac cycle (Fig.2, “Output signal”). Signals "Output signal" in Fig.2 and "O" in Fig.3 represent the same output trigger 11. The moment of transition of the trigger 11 of the state “1” in state “0” is taken as the beginning of the next cardiac cycle.

Values U you can choose from the following considerations. The maximum frequency spectrum of the P-wave is in the region of 5-10 Hz, the amplitude of the R-wave is 0.02-0.2 amplitude R-wave. Additive noise due to the above factors can have a frequency up to 1 Hz and an amplitude comparable to the amplitude of the R wave. Thus, Realnum signal with the current settings listed above. Under these conditions, the maximum values of the modulus of the difference of the second order are estimated by the following expression:

for P-wave

where Upthe amplitude of the R-wave,

TP- the duration of the R-wave,

Td - sampling period,

for additive noise

where UNthe amplitude of the additive noise,

TN- period of signal interference.

The above expressions are obtained taking into account the fact that the sampling period Td is much less periods of sinusoidal signals 2Tpand TNdescribing P-wave and additive noise. Then for the initial phase of the P-wave first non-zero discrete reference that defines the maximum value of the difference of the 2nd order, has an amplitude ofi.e. is determined by the expression (1).

For a sinusoidal signal, describing the additive noise, the maximum value of the module of differentials of the second order are moments in time1/4TN,3/4TNetc., In the neighborhood of these points, the modulus of the difference of the second order is determined by the expression

.

Using the known ratio of Sin(/2±x)=Cos(x) and representing Cos(x) Rena series we obtain the expression (2).

Module threshold level must be greater than the maximum value of the module of differentials of the 2nd order interference signal ddN and less than the maximum value of the module of differentials 2-th order signal for P-wave ddP. The greatest immunity highlight the beginning of the cardiac cycle is achieved, if the threshold level is at equal distance from ddN and ddP:

The worst conditions to select the beginning of the cardiac cycle, coinciding with the beginning of P-wave, generated when a P-wave has a minimum amplitude and the maximum duration, and the additive noise is the maximum amplitude and maximum frequency. From the above possible parameters P-wave and the worst additive noise conditions will be when Up=0.02 URwhere URthe R wave amplitude (usually about 1 mV), TP=0.1 s, UN=UR, TN=1 C. expression(1), (2), (3) get ddN110-3URddP310-3UR, Uop=210-3UR.

For convenience, the technical implementation of the comparison signals of the differences of the second order with the threshold levels listed with the, the fact of Fig.2 shows the signal at the output of the block forming the differences of the second order, the implemented schema-based sample-and-hold and operational amplifiers. The resulting difference signal of second order is amplified 1000 times. At the same time the signal difference of the 2nd order and the threshold signals have values of the order of units of volts, which provides a relatively simple implementation comparison of these signals, such as conventional Comparators.

Technical and economic effect of the proposed invention is to improve the reliability of the selection to the beginning of each cardiac cycle, coinciding with the beginning of P-wave, regardless of possible deviations from normal parameters (shape, amplitude, duration) teeth cardiomegaly, in particular QRS complex, drift and contour caused by the action of the FORMER additive low-frequency noise (impact breathing, artifacts, time drift, etc). A reliable determination of the beginning of each cardiac cycle, coinciding with the beginning of P-wave, improves conditions for processing cardiomegaly (calculation time parameters of individual elements of cardiomegaly, the computation of the duration of cardiocycle, averaging multiple cardiocycle sync the beginning of the R-wave, etc., No. 20.

2. RF patent №2195164, And 61 In 5/02. The way to select the beginning of the cardiac cycle and the device for its implementation /A. A. Mikheev //BI 2002, No. 36.

Claims

Device to select the beginning of the cardiac cycle that contains the filter, the inlet of which is the input of the block sample rate generator control pulses, two source threshold levels, the unit of comparison, the two schemes And the pulse counter, the output of the filter connected to the first input of the block sampling, to the second input of which is connected to the first generator output control pulses, a second input unit of comparison is connected to the output of the first source threshold level, and a third input to the output of the second source threshold level, the output of the Comparer connected to the first input of the first circuit, And characterized in that that it was additionally introduced the block forming the differences of the second order and the trigger, and the input processing unit differences of the second order is connected to the output of block sampling, and the output connected to the first input of the comparison, the output of the Comparer is connected to the input of the zero pulse counter and the trigger input setup unit trigger is connected to the output of the second circuit And the trigger output avlh pulses, and it is with a counter input counter pulse, the bit outputs of which are connected to corresponding inputs of the second circuit I.

 

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