JPH0375169B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a pulse wave detection device that suitably detects pulse waves generated from the arteries of the human body.

BACKGROUND ART For example, when a part of a human body is compressed with a cuff when measuring blood pressure, pressure vibrations synchronized with the human body's heartbeat are generated within the cuff. For example, JIS T
In an oscillometric blood pressure measuring device such as that specified in 1115, the pressure vibration is detected as a pulse wave, and blood pressure measurement is performed based on the amplitude change of the pressure vibration. Basically, the pulse wave generated from the artery in synchronization with the heartbeat is included, but also its harmonics and motion artifact noise generated in relation to the body movement of the subject. Therefore, in order to improve measurement accuracy, noise is removed by passing the signal representing the pressure vibration through a band filter that discriminates pulse waves in terms of frequency, and the output signal from the band filter is used as a pulse wave signal. The blood pressure is supplied to a blood pressure measurement circuit.

Problems to be Solved by the Invention By the way, the above-mentioned bandpass filters conventionally used to remove noise have a constant bandwidth, and are suitable for blood pressure measurement on a wide range of subjects, from the elderly to children. In order to make this possible, the bandwidth of the above-mentioned band filter is set to be relatively wide. For this reason, such a band filter does not remove noise components sufficiently, and the signal that has passed through the band filter may include not only the pulse wave synchronized with the heartbeat but also other noise components. When measuring blood pressure, etc., there were cases where measurement accuracy could not be obtained due to the noise.

The present invention has been made against the background of the above circumstances, and an object thereof is to provide a pulse wave detection device that suitably detects pulse waves generated in synchronization with heartbeat.

Means for Solving the Problems The gist of the present invention to achieve the above object is to provide a pulse wave detection device for detecting pulse waves generated in synchronization with heartbeat, which includes: detects vibrations related to arterial wall movement synchronized with
a vibration sensor that outputs a vibration signal representing the vibration; (b) a pulse detection means that detects a pulse period or a number of pulses per unit time from the vibration signal; and (c) a pre-stored pulse period or number of pulses per unit time. Pulse wave fundamental frequency calculation for calculating the actual fundamental frequency of the pulse wave based on the pulse rate detected by the pulse rate detection means or the pulse rate per unit time from the relationship between the pulse rate and the fundamental frequency of the pulse wave. (d) a plurality of types of narrowband filters having different frequency bands for discriminating pulse waves having different fundamental frequencies; and (e) a means for discriminating pulse waves having different fundamental frequencies; The present invention further includes filter selection means for selecting a filter suitable for discriminating the signals provided, passing the vibration signal, and discriminating the signal representing the actual pulse wave from the vibration signal.

Operation In this way, as shown in the claim correspondence diagram in FIG. 4, the pulse wave fundamental frequency calculation means can calculate the difference between the pre-stored pulse period or pulse rate per unit time and the fundamental frequency of the pulse wave. From the relationship, when the fundamental frequency of the actual pulse wave is calculated based on the pulse rate or the number of pulses per unit time detected by the pulse rate detection means, the filter selection means selects pulse waves having different fundamental frequencies. A filter suitable for discriminating a signal having the fundamental frequency of the actual pulse wave is selected from among a plurality of types of narrow band filters having different frequency bands for discrimination, and a filter is selected that allows the vibration signal to pass through. By this, the signal representing the actual pulse wave is discriminated from the vibration signal.

Effects of the Invention In this way, since the vibration signal is passed through a narrow band filter that matches the fundamental frequency of the actual pulse wave, a pulse wave with noise suitably removed can be obtained. Therefore, by using such a pulse wave for blood pressure measurement, for example, high measurement accuracy can be obtained.

Here, the pulse wave included in the pressure vibration within the cuff appears in synchronization with the pulsation of the human body. On the other hand, the Korotkoff sound (K sound) used in conventional blood pressure measurement also appears in synchronization with the pulsation of the human body, but the frequency of its fundamental wave is generally around 40Hz, and the number of pulsations of the person being measured is Or, there is no correlation at all with the beating period. However, as a result of the inventor's analysis of the frequency of the pulse wave shown in Fig. 1, as shown in Fig. 2, the fundamental frequency of the pulse wave has the minimum frequency among the respective frequency values at each peak. It has become clear that the linear correlation shown in FIG. 3 holds between the fundamental frequency and the number of pulsations or pulsation period per unit time of the person being measured. In the present invention, the fundamental frequency of the pulse wave collected for each subject is easily determined based on the correlation between the pulse wave included in the pressure vibration within the cuff and the pulse frequency or number of pulses of the subject. There is great significance in the way it is done. For example, if one were to select multiple narrowband filters prepared in advance using conventional technology, the pulse wave of each subject would be collected and then analyzed using an expensive and large frequency analyzer (spectrum analyzer).
The fundamental frequency had to be determined using

Since the pressure vibrations within the cuff are mainly composed of pulse waves, the pulsation period or number of pulsations per unit time is determined based on the pressure oscillations to detect pulsations (occurrence of pulse waves). Alternatively, the output signal of a well-known electrocardiograph or pulse rate monitor may be used.

The predetermined relationship shown in FIG. ), and the actual fundamental frequency may be determined by performing a logical operation using the table and the actual pulse period or number of pulses per unit time.

In addition, multiple types of narrowband filters may be configured by a combination of individual filters that regulate the high and low frequencies in the signal transmission path, and the allowable frequency bands may partially overlap. Of course, it is okay to leave it alone.

Embodiment Hereinafter, an oscillometric automatic blood pressure measuring device to which an example of the pulse wave detecting device of the present invention is applied will be described in detail based on the drawings.

In FIG. 5, reference numeral 10 denotes a well-known long glove-shaped cuff that is wrapped around a part of the human body such as the upper part of the body or the thigh. A pump 12, a pressure sensor 14 that detects the pressure inside the cuff 10 and outputs a pressure signal SP representing the pressure, a quick exhaust valve 16 that exhausts the air inside the cuff 10 to rapidly lower the pressure inside the cuff 10, A constant speed exhaust valve 18 is connected in parallel to gradually exhaust the air inside the cuff 10 so that the pressure inside the cuff 10 drops at a rate suitable for blood pressure measurement. Note that 20 is a throttle inserted between the constant speed exhaust valve 18 and the cuff 10 to determine the rate of pressure drop during constant speed exhaust.

The pressure signal SP passes through an amplifier 22 and is passed through a low-pass filter 24, a first filter 26, a second filter 28, a third filter 30, a fourth filter 32,
and is supplied to the waveform shaping circuit 34. The low-pass filter 24 filters the cuff 10 included in the pressure signal SP.
The pressure value signal PV, which is intended to pass only the signal corresponding to the static pressure value of , and from which the alternating current component (vibration component) has been removed, is supplied to the A/D converter 36, and the A/D converter 36 Pressure value signal PV
The pressure value represented by is converted into a code signal and supplied to the I/O port 38.

The first filter 26, the second filter 28, the third filter 30, and the fourth filter 32 are narrow band filters each having a different passable frequency band, and as shown in FIG. The range of variation due to individual differences in the fundamental frequency of the pulse wave is covered by this series. In other words, the fundamental frequency of the pulse wave generally varies depending on the person being measured.
For example, the first filter 26 has a passable band of 2.6 to 3.33Hz, and the second filter 28 has a passable band of 2.0 to 2.6Hz. A third filter 30 with a pass tolerance band of 1.4 to 2.0 Hz, and a 0.67
4th filter 3 with a pass tolerance band of ~1.4Hz
It is covered by 2. And those filters 26, 28, 30, 32 are
When a pulse wave in its own passable band is present in the pressure signal SP, a pulse wave signal SM representing the pulse wave is supplied to each port P ₁ , P ₂ , P ₃ , P ₄ of the multiplexer 40, respectively.

The waveform shaping circuit 34 receives the input pressure signal SP.
A pulse-like pulse signal PP synchronized with the pulsation (pulse) of the subject is formed from the pulse rate calculation circuit 44.
supply to. That is, the pressure vibration of the cuff 10 represented by the pressure signal SP is as shown in FIG.
Since it is mainly composed of pulse waves that are generated in synchronization with the pulse rate of the person being measured, by detecting the peak or the level near the peak, the pulse wave can be synchronized with the pulse rate of the person being measured. The pulse signal PP is shaped into a pulse signal shown in FIG.

The pulse period calculation circuit 44 calculates the period T of the pulse signal PP.
is calculated, and a period signal SY, which is a pulse signal representing the actual pulse period T of the subject, is supplied to the filter selection circuit 46. Normally, the pulse period calculation circuit 44
consists of a reference signal generator and a counter that counts the signals from the reference signal generator, is reset by the pulse signal PP, and outputs the count contents at the time of reset as a periodic signal SY,
The pulse generation cycle of the pulse signal PP is detected. That is, the waveform shaping circuit 34 and the pulse rate calculation circuit 44 form the pulse rate detection means.

The filter selection circuit 46 is a pulse wave fundamental frequency calculation means, and supplies a selection signal SL to the port selection terminal PS of the multiplexer 40 based on the pulse period T of the subject represented by the periodic signal SY. The multiplexer 40 selectively selects one of its input ports P ₁ to _{P 4} based on the selection signal SL, and selects the pulse wave signal supplied thereto.
The SM is passed through the A/D converter 48. That is, the filter selection circuit 46 includes a third
A table representing the relationship between the beating period T shown in the figure and the fundamental frequency F of the pulse wave is stored in advance,
The fundamental frequency F of the pulse wave is determined by a logical operation from the table and the periodic signal SY, and a selection is performed to select a filter having filtering characteristics suitable for discriminating the pulse wave having the fundamental frequency F. Signal SL is output. For example, if the period T expressed by the periodic signal SY is 0.38 or less, input port P ₁
, input port P ₂ when period T is 0.38 to 0.5, input port P ₃ when period T is 0.5 to 0.7, and input port P ₄ when period T is 0.7 or more. The select signal SL for selecting
It is output from the filter selection circuit 46.
Therefore, the filters 26, 28, 30, 32 and the multiplexer 40 form a filter selection means for selecting a filter suitable for the fundamental frequency F of the actual pulse wave, and this filter selection means, the pulse rate detection means and the calculation The means form the pulse wave discrimination device 47. Note that the filter selection circuit 46 stores in advance a table representing the relationship between the number of beats per unit time and the fundamental frequency of the pulse wave, and the pulse rate detection means detects the actual number of beats and selects the pulse wave based on the number of beats. The fundamental frequency may also be determined.

The A/D converter 48 converts the pulse wave signal SM into a code signal and supplies it to the I/O port 38.
Starting from 0, the activation signal SS is supplied by the pressing operation. The I/O port 38 has a CPU 52, ROM 54,
RAM56 is connected. The CPU 52 is
According to the program stored in the ROM 54 in advance, signal processing is performed using the temporary storage function of the RAM 56, and the air pump 12, quick exhaust valve 16,
and a pump start signal to the constant speed exhaust valve 18, respectively.
AP, rapid exhaust signal EQ, and constant speed exhaust signal ES are supplied, and the blood pressure value is determined based on the change in the magnitude of the pulse wave signal SM supplied from the A/D converter 48, and the blood pressure value is displayed on the blood pressure display device 58. A blood pressure value signal SD for displaying the measured blood pressure is supplied. Therefore, they are CPU52, ROM54,
The RAM 56, blood pressure display device 58, and the like form blood pressure measuring means.

Hereinafter, the operation of this embodiment will be explained according to the flowchart shown in FIG.

First, step S1 is executed, and it is determined whether or not the start switch 50 has been operated. Step S1 is repeated while the start switch 50 is not operated, but when the start switch 50 is operated and the start signal SS is supplied to the I/O port 38, step S2 is executed. In step S2, the supply of the rapid exhaust signal EQ and the constant speed exhaust signal ES to the rapid exhaust valve 16 and the constant speed exhaust valve 18 is prohibited, and the rapid exhaust valve 16 and the constant speed exhaust valve 18 are closed. , a pump activation signal AP is supplied to the air pump 12, and the air pump 12 is driven. As a result, the pressure within the cuff 10 is increased, as shown in the OA section of FIG.

Next, step S3 is executed, and the pressure value signal PV
It is determined whether the actual pressure P within the cuff 10 represented by is higher than the maximum pressure PM, which is set in advance to be equal to or higher than the expected systolic blood pressure. The actual pressure P is the maximum pressure
If the actual pressure P exceeds the maximum pressure PM, step S3 is repeated, but as soon as the actual pressure P exceeds the maximum pressure PM, step S4 is executed, and the pump activation signal AP that had been supplied to the air pump 12 until then is output. is prohibited, and the driving of the air pump 12 is stopped. Then, step S5 is executed, the constant speed exhaust signal ES is supplied to the constant speed exhaust valve 18, the constant speed exhaust valve 18 is opened, and the pressure within the cuff 10 starts to decrease. Point A in FIG. 9 shows this state.

Thereafter, step S6 is executed to measure blood pressure, and the blood pressure display device 58 displays the systolic blood pressure value and the diastolic blood pressure value.

Here, in the blood pressure measurement in step S6, a so-called vibration method is used, and the blood pressure value is measured based on the magnitude of the pulse wave represented by the pulse wave signal SM. Therefore, in order to maintain measurement accuracy, it is necessary to It must be an accurate extraction of the pulse waves contained in the pressure vibrations. That is, in addition to the fundamental wave of the pulse wave, the pressure vibration of the cuff 10 includes the second and third waves of the pulse wave.
A narrow band filter that selectively passes the fundamental frequency of the pulse wave is necessary because it contains various noises such as high-order harmonics such as It is desirable to distinguish the pulse wave from the pressure vibration of the cuff 10 using For example, a bandpass filter was used that passed signals with a frequency of about 0.8 to 10 Hz. Therefore, even if such a filter is used, noise passing through that band cannot be removed, and the accuracy of blood pressure measurement is limited.

However, according to the present embodiment, the pulse period T of the subject is detected based on the pressure vibration of the cuff 10 that appears as the pressure inside the cuff 10 approaches a preset maximum pressure PM, and The actual fundamental frequency of the pulse wave is determined from the relationship between the pulse period T and the fundamental frequency of the pulse wave, and a filter suitable for the fundamental frequency is selected, so that the cuff 10 represented by the pressure signal SP is The pulse wave can be suitably discriminated from the pressure oscillations prior to blood pressure measurement. That is, the cuff 1 represented by the pressure signal SP
The pressure vibration at 0 is mainly composed of pulse waves that are synchronized with the pulse rate, and forms a periodic waveform that is synchronized with the pulse rate.Using this periodic waveform, the waveform shaping circuit 34 converts the waveform into a pulse shape. Convert the pulse rate signal PP to the actual pulse rate T of the subject from the pulse signal PP.
is calculated, and a periodic signal SY representing its period T is generated.
is from the pulse period calculation circuit 44 to the filter selection circuit 4.
6. And the filter selection circuit 46
As mentioned above, the fundamental frequency F of the pulse wave is determined based on the actual pulse period T from the stored relationship shown in FIG. A selection signal SL for selecting a filter having the characteristic is supplied to the multiplexer 40 in correspondence with the actual pulse period T of the subject. For example, when the actual pulse period T of the subject is 0.6 seconds, the select signal SL for selecting the input port _P3 is supplied to the multiplexer 40, and the third filter 3
0 is selected. This third filter 30
is a narrow band filter as shown in FIG. 6, and therefore only signals near the fundamental frequency of the pulse wave of the subject are discriminated from the pressure vibrations of the cuff 10 and supplied to the A/D converter 48. As a result, even if the fundamental frequency of the pulse wave varies from subject to subject, only signals around the fundamental frequency of the pulse wave are used for blood pressure measurement, resulting in high blood pressure measurement accuracy.

Returning to FIG. 8, when blood pressure measurement is completed, step S7 is executed and a rapid exhaust signal EQ is supplied to the rapid exhaust valve 16. For this reason, the quick exhaust valve 1
6 is opened and the pressure within the cuff 10 is rapidly reduced. Point E in FIG. 9 shows this state.

In this way, according to this embodiment, the fundamental frequency of the pulse wave, which differs for each subject, can be easily determined by detecting the pulse period of the subject without using a spectrum analyzer. Based on the determined fundamental frequency, a narrow band filter is selected that passes only signals around the fundamental frequency of the actual pulse wave. Therefore, high-order harmonics of the pulse wave and noise mixed in the pressure vibrations of the cuff 10 can be removed very easily, and blood pressure measurement accuracy can be maintained at a high level.

Next, an oscillometric automatic blood pressure measuring device to which another embodiment of the present invention is applied will be described. still,
Parts common to those in the previous embodiment are designated by the same reference numerals, and description thereof will be omitted.

In FIG. 10, the pulse-like pulse signal PP output from the waveform shaping circuit 34 is
8 and based on its pulse signal PP,
The select signal SL for selecting the input ports P ₁ to _{P 4} of the multiplexer 40 is determined according to a program stored in the ROM 54 in advance.

That is, the operation for performing such a determination process will be explained according to the flowchart of the fundamental frequency determination subroutine shown in FIG. The pulse period T is calculated, and the step as a pulse wave fundamental frequency calculation means
SS2 is executed and the actual fundamental frequency F is determined based on the pulse period T. That is, the third
A table representing the relationship between the fundamental frequency of the pulse wave and the pulse period shown in the figure is stored in advance in the ROM 54, and the fundamental frequency F of the actual pulse wave is determined from the pulse period T determined in step SS1 and the table.
is determined. And step SS3
is executed to determine whether the actual fundamental frequency F is greater than the predetermined frequency _F1 .
If the fundamental frequency F of the actual pulse wave is greater than the predetermined frequency _F1 , step SS4 is executed, and the input port _P1 is selected to allow the output signal from the first filter 26 to pass through. A select signal SL is supplied from the I/O port 38 to the multiplexer 40. In step SS3,
The actual fundamental frequency F is a predetermined frequency F ₁
, its actual fundamental frequency F
is between predetermined frequencies F ₁ and F ₂ . If the actual fundamental frequency F is between them, step SS6 is executed and a select signal SL is supplied to the multiplexer 40 to select the input port P ₂ in order to allow the output of the second filter 28 to pass through. do. In step SS5, if the actual fundamental frequency F is smaller than the predetermined frequency _F2 , step SS7 is executed, and the actual fundamental frequency F is between the predetermined frequencies _F2 and _F3 . It is determined whether or not.
If the actual fundamental frequency F is between them, step SS8 is executed and a select signal SL for selecting the input port _P3 is supplied to the multiplexer 40, but if the actual fundamental frequency F is between them, If the frequency F is less than ₃ , the input port
A select signal SL for selecting _P4 is supplied to the multiplexer 40. That is, steps SS3 to SS9 are the filters 26, 28, 3.
0, 32, and multiplexer 40 form filter selection means. In addition, step
In SS2, the fundamental frequency of the pulse wave and the pulse period T
It is also possible to store the relationship between the two in advance in the ROM 54 using a functional formula, and to calculate the fundamental frequency F of the pulse wave based on the functional formula and the pulse period T determined in step SS1. Of course.

The subroutine consisting of steps SS1 to SS9 described above can be executed after the pulse wave is captured as pressure vibration of the cuff 10 and before blood pressure measurement starts, so it is not necessary to perform the subroutine in the flowchart of FIG. From step S1 to step S6
The blood pressure measuring operation similar to that of the above-mentioned embodiment is performed by inserting the blood pressure somewhere between the two.

In this way, according to this embodiment, the fundamental frequency F of the actual pulse wave is easily determined, and a narrowband filter suitable for the fundamental frequency F is selected, so that the same In addition to this effect, since the pulse period T and the fundamental frequency of the actual pulse wave are calculated according to a pre-stored program, there is an advantage that the pulse period calculation circuit 44 and the filter selection circuit 46 are not required. be. Therefore, the above-mentioned waveform shaping circuit 34 and step SS
1 forms the pulse rate detection means, and steps SS2 to SS9 form the calculation means.

The above-mentioned embodiment is merely one embodiment of the present invention, and the present invention can be modified in various ways without departing from the spirit thereof.

[Brief explanation of drawings]

FIG. 1 is a chart showing pressure oscillations within the cuff in relation to voltage and time. FIG. 2 shows a diagram obtained by frequency analysis of the vibration shown in FIG. 1. FIG. 3 is a chart showing the relationship between the fundamental frequency of the pulse wave and the beat period or number of beats. FIG. 4 is a diagram corresponding to claims of the present invention. FIG. 5 is a diagram showing the configuration of a blood pressure measuring device that is an embodiment of the present invention. Figure 6 shows the fifth
It is a chart showing the characteristics of each filter provided in the embodiment shown in the figure. FIG. 7 is a diagram showing a waveform of a pulse signal formed from the pressure vibrations of FIG. 1. 8th
The figure is a flowchart illustrating the operation of the embodiment of FIG. FIG. 9 is a chart showing the time change in the cuff internal pressure and the accompanying time change in the pulse wave during the operation of the embodiment shown in FIG. Figure 10 shows
5 is a diagram showing another embodiment of the present invention and corresponding to FIG. 5. FIG. FIG. 11 is a flowchart illustrating the operation of the embodiment of FIG. 9. 10: Cuff, 14: Pressure sensor (vibration sensor),
{26, 28, 30, 32: filter, 40: multiplexer} (filter selection means), {34: waveform shaping circuit, 44: pulse period calculation circuit} (pulse detection means), 46: filter selection circuit (pulse wave basics) frequency calculation means), {52: CPU, 54: ROM, 5
6: RAM, 58: Blood pressure display device} (blood pressure measurement means), SP: Pressure signal (vibration signal), Step SS
1: Pulse detection means, Step SS2: Pulse wave fundamental frequency calculation means.

Claims (1)

[Scope of Claims] 1. A pulse wave detection device for detecting a pulse wave generated in synchronization with a heartbeat, which detects vibrations related to movement of an artery wall in synchronization with the heartbeat, and represents the vibrations. a vibration sensor that outputs a vibration signal; a pulse detection means that detects a pulse period or a pulse rate per unit time from the vibration signal; and a pre-stored pulse period or pulse rate per unit time and a fundamental frequency of the pulse wave. From the relationship, pulse wave fundamental frequency calculation means calculates the fundamental frequency of an actual pulse wave based on the pulse rate period or pulse rate per unit time detected by the pulse rate detection means; selecting a plurality of types of narrowband filters each having a different frequency band for discrimination; and a filter suitable for discriminating a signal having the fundamental frequency of the actual pulse wave from among the plurality of types of filters; A pulse wave detection device comprising: filter selection means for passing the vibration signal and discriminating a signal representing the actual pulse wave from the vibration signal.