JPH0556139B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a non-invasive digital blood pressure monitor, and particularly to a non-invasive digital blood pressure monitor that identifies and removes extraneous noise that is mixed in during blood pressure measurement, and eliminates the influence of impulse noise on the cuff or body movement. The present invention relates to a non-invasive digital blood pressure monitor that can perform reliable blood pressure measurements without undergoing blood pressure.

[Prior art and its problems] Non-invasive digital blood pressure monitors are generally based on automatic recognition of Korotkoff sounds. by the way,
With this type of device, it is necessary to recognize the onset and disappearance of Korotkoff sounds without human intervention, but the volume is very weak, so when controlling the cuff pressure,
Alternatively, it is susceptible to noise caused by the subject's body movements, making blood pressure measurement difficult.

For this reason, various extraneous noise removal methods have been proposed in the past. For example, (1) the pulse wave gate method does not recognize the output from the microphone as a Korotkoff sound when there is no pulse wave as a condition for the generation of Korotkoff sounds.
(2) The pattern recognition method performs pattern recognition of microphone input waveforms based on basic pattern information regarding Korotkoff sounds. (3) The multi-point microphone method places microphones at several points below the cuff to separate noise and Korotkoff sounds. The methods (1) and (2) above have been conventionally used and have already been commercialized. but
In the pulse wave gate method (1), the noise generated by body movements also changes the cuff internal pressure, which causes the pulse gate to open at the same time, often causing malfunctions. Also (2)
In the pattern recognition method, it was impossible to separate and identify the impulse noise waveform applied to the microphone and the Korotkoff waveform because they were very similar. In addition, in the case of the multi-point microphone method (3), the propagation of the noise applied to the arm is not isotropic, resulting in various propagation delays and amplitude attenuations, and since these vary depending on the subject, the gain and phase correction of each channel is necessary. It could not be carried out completely and the effect could not be achieved.

[Purpose] The present invention has been made in view of the above-mentioned drawbacks of the prior art, and its purpose is to identify and eliminate extraneous noise mixed in during blood pressure measurement, and to eliminate impulse noise to the cuff or To provide a non-invasive digital blood pressure monitor capable of reliable blood pressure measurement without being affected by body movements or the like.

[Summary of the invention]

In order to achieve the above object, the present invention provides a K and C sound microphone attached through a cuff having an inelastic structure, and a pulse pressure detector that detects the pulse pressure component of the cuff pressure and outputs a pulse pressure signal. a K-sound for detecting a pulse sound and a Korotkoff sound at a part to be measured with the K-sound microphone, extracting a signal corresponding to the Korotkoff sound from an output signal of the K-sound microphone and outputting the extracted signal as a K-sound signal; detecting means, detecting the pulse sound transmitted through the cuff and noise generated by the cuff with the C sound microphone, and extracting a signal corresponding to the noise from the output signal of the C sound microphone; a C sound detection means for outputting the K sound signal as a C sound signal; and noise for determining whether or not the K sound signal is noise based on the relationship between the pulse pressure signal, the K sound signal, and the generation time of the C sound signal. It is characterized by comprising an identification means.

The C sound detection means may include the C sound microphone and a high-pass filter connected to the output side of the microphone to block sound signal components below a predetermined frequency.

Further, the C-sound microphone may be provided superimposed on the K-sound microphone with a very small distance therebetween.

Furthermore, the low cutoff frequency of the high-pass filter can be set to approximately 100Hz.

Furthermore, the noise identifying means can recognize the K sound signal as noise when the C sound signal is recognized to have occurred within 20 ms before and after the occurrence of the K sound signal.

[Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[First Embodiment] FIG. 1 is a block diagram showing a digital blood pressure monitor according to a first embodiment of the present invention. In the figure, 1 is a cuff wrapped around the subject's upper arm, 2 is a C-sound microphone (cuff-side microphone) that detects sound transmitted through cuff 1, and 3 is a sensor that detects Korotkoff sound at the measurement site (brachial artery flow). 4 is a pipe that guides the internal pressure of the cuff 1, and 5 is the main body of the digital blood pressure monitor of the embodiment.

Furthermore, in the main body 5, 6 is a pressure sensor that detects the cuff internal pressure guided through the pipe 4 and converts it into an electrical signal RP, and 7 is a cuff pressure signal RP output from the pressure sensor 6.
An A/D converter 8 samples the cuff pressure signal RP at a predetermined period and converts it into a digital signal P, and an A/D converter 8 outputs the pulse pressure signal RP' by blocking the DC component of the cuff pressure signal RP and passing only the pulse pressure vibration component. a filter (usually composed of a bandpass filter BPF), and a comparator 9 that rectifies the pulse pressure signal RP' and compares its amplitude with a predetermined threshold to form and output a binary pulse pulse signal PUL. COMP), 10 is a K sound signal by amplifying the detection signal of the K sound microphone 3.
An amplifier (AMP) that outputs RKA; 11 is a K sound filter (also composed of a bandpass filter BPF) that passes only the Korotkoff sound signal component of the K sound signal RKA and outputs the K sound signal RKA';
12 is a comparator (COMP) which rectifies the K sound signal RKA' and compares its amplitude with a predetermined threshold value to form and output a binarized K sound signal KA; 13;
amplifies the detection signal of the cuff side microphone 2 and generates a C sound signal.
An amplifier (AMP) that outputs RKC, and 14 a C sound filter (one aspect of the present invention is a high-pass filter) that cuts off frequency components of a C sound signal RKC below a predetermined value (for example, 100Hz) and outputs a C sound signal RKC'.
HPF), 15 is a comparator (COMP) which rectifies the C sound signal RKC' and compares its amplitude with a predetermined threshold to form and output a binarized C sound signal KC, and 16 is the same as described above. Various digital signals (cuff pressure signal P, pulse pulse signal PUL, K sound signal KA, C sound signal KC) are input, noise (artifacts) are identified and removed based on a predetermined relationship between the signals, and the subject's systolic blood pressure SYS is determined. 17 is the central processing unit (CPU) that judges the diastolic blood pressure DIA, and 17 is the blood pressure value SYS and DIA that are the judgment results.
This is a display section that displays the following information.

2 to 5 relate to the explanation of the operating principle of the blood pressure monitor of this embodiment, and FIG. 2 is a cross-sectional view of the cuff 1 showing one mode of use of the C-sound microphone 2 and the K-sound microphone 3, and FIG. 3 is a sectional view of the cuff 1. FIG. 2 is a diagram showing the main signal waveforms of FIG. 1 observed in a state without noise (artifacts).
In FIG. 2, the K-sound microphone 3 is placed on the artery near the elbow of the upper arm, and its sound detection surface faces in the direction of arrow b (towards the upper arm). In addition, the C sound microphone 2 is
The sound microphone 3 is placed back-to-back (overlapping) with a minute distance apart, and its sound detection surface is indicated by the arrow a.
direction (cuff side). In this configuration, when the pressure of the cuff wrapped around the upper arm is increased to 150 to 200 mmHg and then gradually reduced, the blocked arterial flow begins to flow under the cuff in the direction of arrow c, in synchronization with the heartbeat. By capturing pulse pressure changes occurring within the cuff with the pressure sensor 6, a pulse pressure signal RP' and a pulse pulse signal PUL as shown in FIG. 3 are obtained. The pulse pulse signal PUL is, by its nature, generated before the Korotkoff sound and disappears after it disappears,
Moreover, since minute displacements under the upper arm cuff due to arterial flow are captured by the entire cuff pressure contact surface 18, the pulse width is sufficiently large and is generally used as a pulse gate signal for identifying Korotkoff sounds. Also, before systolic blood pressure SYS is determined (before SYS)
At this time, a pulse sound signal ma (on the K sound signal RKA in FIG. 3) is detected by the K sound microphone 3. Since this pulse sound has a low frequency component, it is transmitted through the cuff 1 and is also captured by the C sound microphone 2. This is the cuff side pulse sound signal mc (on the C sound signal RKC in FIG. 3). As cuff 1 continues to decompress, it enters the SYS section in Figure 3.
The K-sound microphone 3 detects a so-called Korotkoff sound signal Ka in which the arterial blood flow under the cuff collides with the stationary arterial blood on the peripheral side and causes the blood vessel wall to vibrate.
The time tpa from the generation of the pulse pulse signal PUL to the generation of the Korotkoff sound signal Ka is usually roughly determined by the size and structure of the cuff 1 and the insertion position of the microphone 3, and is normally determined under normal conditions. is recognized within a given time range as long as the Korotkoff sound is captured. On the other hand, since the Korotkoff sound signal Ka has a high frequency component, it is normally blocked by the inelastic structure of the cuff 1 and cannot be captured by the C sound microphone 2. Therefore, only the pulse sound signal mc is detected from the C sound microphone 2 even in the SYS section. The above is the same up to the subsequent DIA section and also for the section after DIA. Here, the present invention has been developed in view of the above conditions, that is, in the absence of noise, the K sound microphone 3 detects a superimposed signal of the pulse sound signal ma and the Korotkoff sound signal Ka, and the C sound microphone 2 detects a pulse sound signal. By utilizing the fact that only the signal ma is detected, artifacts caused by body movements and disturbances are identified and removed from the true Korotkoff sound signal.

FIG. 4 is a diagram showing the relationship between the frequency spectrum of the K sound signal RKA and the frequency characteristics of the C sound filter 14. As shown in Fig. 3, the K sound signal RKA is the Korotkoff sound signal Ka with respect to the low frequency component pulse sound signal ma.
The characteristic sharp notches in the positive and negative directions are superimposed, and frequency analysis of this results in the spectrum characteristic SPrka shown in Figure 4. And almost 0
It can be seen that the frequency range up to ~100 Hz contains the pulse sound signal ma, the Korotkoff sound signal Ka, and, if present, a low frequency noise component n. Furthermore, by analyzing more K sound signals RKA, it was found that the characteristic signal components are in the range of 20 to 80 Hz. Therefore, components exceeding approximately 100 Hz are essentially distinguishable from the K sound signal RKA, and can be excluded as noise (artifact). Therefore, the C sound filter 14 of the embodiment is constituted by a high pass filter HPF whose low cutoff frequency is fc (octave -3 dB at approximately 100 Hz), an example of which is shown by the characteristic Ghpf in FIG.
In addition, when there is no noise, the pulse sound signal is sent to the C sound microphone 2.
Since only mc is detected, the low cutoff frequency fc of the C sound filter 14 may be further lowered.
However, since the pulse sound component and the K sound component overlap deeply, 100 Hz was adopted as fc in the example. Now, by passing the C sound signal RKC through the C sound filter 14 having the above characteristics, if a high frequency signal component transmitted through the cuff 1 is detected, this can be a condition for determining it as noise. For example, an impulse impact when one point on the cuff is hit directly, or cuff 1
This is because when the upper upper arm or the lower arm near the elbow is struck, the impact is detected not only by the pressure sensor 6 and the K sound microphone 3 but also by the C sound microphone 2. Moreover, the time during which this impact is transmitted varies depending on the relative position of the impact generation point and the pressure sensor 6 and microphones 2 and 3, the constitution of the subject, the measurement environment, etc.
Not uniform. Conventionally, such disturbances caused the pulse pulse signal and the K sound signal to occur simultaneously, causing erroneous measurements. However, according to the present invention, such impact sound is also detected by the C sound microphone 2. Moreover, since such impact sound contains high frequency components, it generates a binary C sound signal KC. Therefore, the C sound signal
When KC occurs, it is determined whether it is noise or not, but as mentioned above, various time differences occur depending on the location where the disturbance is applied and the placement of the microphones 2 and 3. We decided to set a time difference and investigate the relationship between the K sound signal KA and the C sound signal KC.

Figures 5a to 5c are diagrams for explaining a typical noise determination method according to the embodiment based on the mutual relationship of the three signals PUL, KA, and KC, and Figure a shows the case where no C sound signal KC is generated. b and c in the same figure are C tone signals.
When KC occurs and K sound signal KA and C sound signal
This shows a case where the time difference in the occurrence of KC becomes a problem. In this embodiment, this determination is made by the CPU 16, so the time t is calculated by a counter count value (for example,
It is expressed as PACTR, KACTR,...). First, the determination method for the three typical types of the embodiment is shown.[TYPE1] K sound signal KA exists in pulse pulse signal PUL,
K sound signal KA from the rise of pulse pulse signal PUL
The time PACTR until the rise of the K sound signal KA is within a predetermined range (C ₁ ≦PACTR≦C ₂ ), and the K sound signal KA
pulse width KACTR is within the specified range (C ₃ ≦
KACTR≦C ₄ ), the true K sound signal KA
recognized as However, in this case, the C sound signal KC is not generated [Fig. 5a].

Here, a specific example of the above range is shown below. 0mS≦PACTR≦300mS 80mS≦KACTR≦200mS It is.

[TYPE2] K sound signal KA and C sound signal in pulse pulse signal PUL
When KC exists, the time from the rise of the pulse pulse signal PUL to the rise of the K sound signal KA is PACTR
is within a predetermined range (C ₁ ≦ PACTR ≦ C ₂ ), and the pulse width KACTR of the K tone signal KA is within a predetermined range (C ₃ ≦KACTR≦C ₄ ). If the rise of the C sound signal KC is later than the rise of the C sound signal, and the time interval ACCTR is larger than a predetermined value C ₅ determined based on experiments (ACCTR≧C ₅ ), it is treated as a true K sound signal KA. Recognize [Figure 5b].

Here, a specific example of the above range is ACCTR≧20mS. Although this value can be calculated theoretically by taking into account the upper limit of the propagation time of surface acoustic waves from the shock source to each microphone, it has been confirmed experimentally with practicality in mind. be.

[TYPE3] K sound signal KA and C sound signal in pulse pulse signal PUL
When KC exists, the time from the rise of the pulse pulse signal PUL to the rise of the K sound signal KA is PACTR
is within a predetermined range (C ₁ ≦ PACTR ≦ C ₂ ), and the pulse width KACTR of the K tone signal KA is within a predetermined range (C ₃ ≦KACTR≦C ₄ ). If the rise of the C sound signal KC is earlier than the rise of the C sound signal, and the time interval CACTR is larger than a predetermined value C ₅ determined based on experiments (CACTR≧C ₅ ), it is recognized as a true K sound signal KA. [Figure 5c].

Here, a specific example of the above range is shown below. CACTR≧20mS It is.

6 and 7 are flowcharts showing the measurement procedure of the first embodiment, and FIG. 6 is a flowchart showing the main measurement procedure. This process is started by entering the constant evacuation mode after cuff pressurization. In step S1, the contents of various flags and counters are all initialized to zero. Here, the flag PULF
is a flag that is set to logic 1 by detecting the pulse pulse signal PUL, flag KAF is a flag that is set to logic 1 by detecting the K sound signal KA, and flag KCF is set to logic 1 by detecting the C sound signal KC. Flags to be set, counters PACTR~CACTR
The details are as explained in connection with FIG.
In step S2, it is determined whether or not there is a pulse pulse signal PUL. If it is not PUL, the process advances to step S3, and it is checked whether the flag PULF is 1 or not.
If it is not PULF1, the PUL has not yet occurred, so the process returns to step S2 and waits for the PUL. This is because there is no need to determine the presence or absence of the K sound signal KA in a range other than the pulse pulse signal PUL. If PUL is determined in step S2, the process proceeds to step S4, where a flag is flagged to indicate that PUL has occurred.
Set PULF to logic 1. In step S5, the pulse width of each signal and the generation time difference between each signal are measured according to the processing procedure shown in FIG. Step S12
Then, it is determined whether or not blood pressure determination has been completed, and if it has not been completed, the process returns to step S1. In addition, step S described later
In the time counting process in Step 5, since various counters are configured to count unit time Δt, step S
The processing up to returning to 1 is performed in synchronization with the unit time Δt.

In addition, the pulse pulse signal is determined in step S2.
Not PUL, and PULF in step S3
When it is determined that =1, it indicates the end of the one-pulse pulse signal PUL. Therefore, the flow performs noise identification processing from step S6 to step S10. First, in step S6, it is determined that C ₁ ≦CTR≦C ₂ . If the determination is NO, the basic requirements for recognizing the occurrence of a K sound are lacking, so it is determined to be noise, and the process returns to step S1.
Also, if the determination in step S6 is YES, step S
Proceed to step 7 to determine if C ₃ ≦KACTR≦C ₄ . If the determination is NO, it is determined to be noise since it lacks the basic requirements for recognizing that the K sound has occurred, and the process proceeds to step S.
Return to 1. If the determination at step S7 is YES, the process advances to step S8, where it is determined whether the C note flag KCF is 1 or not. If KCF is not 1, C tone signal
This indicates that KC has not occurred, and the determination made so far is sufficient to recognize that the K sound signal has occurred normally, so the flow advances to step S11.
Performs blood pressure determination processing. In the blood pressure determination process, the cuff pressure P at the time of the first true K sound signal KA is determined to be the systolic blood pressure SYS, and then the true K
The cuff pressure P when the sound disappears is the diastolic blood pressure.
This is determined to be DIA. Further, if the systolic blood pressure SYS or the diastolic blood pressure DIA is determined in this process, the blood pressure value is displayed on the display unit 17. Further, if the flag KCF is 1 in the determination at step S8, the process advances to step S9, where it is determined whether ACCTR≧ _C5 . If the determination is YES (large), it is unlikely that an impact sound generated at one point in the assumed range was transmitted, so this is determined to be the K sound signal KA, and the process proceeds to step S11. Also, the judgment is NO (not large)
If so, the process advances to step S10, where it is determined whether CACTR≧ _C5 . As is clear from the relationship between b and c in Figure 5, when ACCTR≧C ₅ , ACCTR
This is because there are two possible cases: ≠0 and smaller than C ₅ and cases where ACCTR=0 and CACTR is counting instead. The determination in step S10 is
If YES (large), the same judgment as in step S9 is made and it is determined to be the K sound signal KA, and the process proceeds to step S11. If the determination is NO (small), it is determined to be noise and the process returns to step S1. in the same way
When CACTR≠0 and C is smaller than ₅ ,
This includes the case where ACCTR=0 and CACTR=0.

FIG. 7 is a flowchart showing details of the timekeeping process. In this process, the pulse pulse signal PUL is input only while it is 1, and time information necessary for determining a true K sound signal is formed. First, in step S51, it is determined whether or not there is a K tone signal KA. If the determination is NO, the process advances to step S52 and the K sound flag is set.
Check whether KAF is 1 or not. If KAF is not 1, this means that the pulse pulse signal PUL has been generated and the K sound signal KA has not yet been generated, so the process advances to step S53 and the counter PACTR is incremented by 1. Further, if it is determined in step S51 that there is a K sound signal KA, a flag KAF is set to 1 in step S54, and a counter KACTR is incremented by 1 in step S55. In this way, while the K sound signal KA is present, the contents of the counter KACTR are updated and the pulse width is counted. Also, the flag
When the K sound signal KA disappears after KAF becomes 1, the process proceeds to steps S51→S52→S56, and time counting is not performed. In step S56, the C tone signal is
Determine whether KC exists or not. If there is no KC, the process advances to step S57 and it is checked whether the K sound flag KAF is 1 or not. When KAF is 1, it is further checked in step S58 whether flag KCF is 1 or not. That is, after the signal is not KC and the flag KAF is 1, step S5 is performed only until the flag KCF becomes 1.
This is to add 1 to the counter ACCTR at 9. In addition, when the flag KAF is 1 and the flag KCF is also 1, instead of the signal KC, the signal KC
Since the pulse width has passed, nothing is counted. Also, if the signal KC is present in the determination at step S56, the process advances to step S60 and the flag KCF is detected.
is set to 1, and the flag KAF is set to 1 in step S61.
Check whether is 1 or not. That is, when the signal KC is applied,
This is because the counter CACTR is incremented by 1 in step S62 until the flag KAF becomes 1. However, after the flag KAF reaches 1, it is not counted. In this way, time information necessary for determining whether or not it is noise is stored as the contents of the counter.

[Second Embodiment] FIGS. 8 and 9 relate to the explanation of the second embodiment,
FIG. 8 is a block diagram of a digital blood pressure monitor that achieves the same noise removal effect with a simple hardware configuration, and FIG. 9 is an operation timing chart thereof. Note that some of the drawings of the same constituent parts as those in FIG. 1 are omitted, or the same numbers are given and the explanation thereof is omitted.
In FIG. 8, 21 and 22 are D-type flip-flops (FF), 23 to 25 are single shot multivibrators (SS), 26 is an OR gate,
27 is an AND gate. In this configuration, the analog pulse signal RP', the pulse pulse signal PUL, the analog K sound signal RKA and K sound signal KA, and the analog C sound signal RKC and C sound signal KC are the same as those shown in FIG. Here, the AND gate 27 whose purpose is to pass only the true K sound signal PULKA, the pulse pulse signal PULF whose occurrence is stored in the FF 21,
The sampling signal SP for judgment generated by triggering at the falling edge of the K sound signal KA, and the C
A prohibition signal that outputs a logic 0 level when the sound microphone 2 detects a high frequency component, treating it as noise contamination.
It is configured with three inputs, INH/, to prevent incorrect blood pressure determination by the CPU 16. Also, at least K
By generating a reset pulse RS2 in synchronization with the rise of the sound signal KA, a single pulse signal can be generated.
Immediately end the judgment process for PUL (FF2
1 and 22), it is possible to quickly discover the next true K sound signal KA, and prevent unnecessary section determination processing. For example, in Fig. 9, when a disturbance occurs at time tn, the pulse pressure signal
There is a noise np in RP', a noise na in the K sound signal RKA,
Noise nc occurs in each of the C sound signals RKC. In this case, the C sound signal RKC contains high frequency components, so 2
A digitized C sound signal KC is generated. Therefore, the signal KC sets the FF 22 at its rising edge, and thereafter keeps the inhibit signal INH/ in the logic 0 state. Therefore SS2
Even if the sampling signal SP is generated from 4, it does not satisfy the AND gate 27, and the CPU 16 can avoid erroneous determination of the K sound signal. Then, the circuit returns to its initial state with the reset signal RS2, and the next true K tone signal can be generated at any time.
PULKA can be detected.

When constructed using hardware as described above, there is no need for complicated determination processing as described with reference to FIG. 6, and no need for statistical processing as shown in FIG. 7. Therefore, not only the memory of the CPU 16 is saved, but also the processing load is reduced, leading to a significant cost reduction.

[Effects of the Invention] As described above, according to the present invention, even when disturbances such as body movements occur, the true K sound can be detected by knowing the mutual time relationship of the pulse pulse signal, the K sound signal, and the cuff side C sound signal. It became possible to recognize signals.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram showing a digital blood pressure monitor according to the first embodiment of the present invention, FIG. 2 is a cross-sectional view of the cuff 1 showing one mode of use of the C-sound microphone 2 and the K-sound microphone 3, and FIG. FIG. 4 is a diagram showing the relationship between the frequency spectrum of the K sound signal RKA and the frequency characteristics of the C sound filter 14. FIG. Figure a is a timing chart when the C sound signal KC is not generated, and Figures b and c are the timing charts when the C sound signal KC is generated, and the problem is the time difference between the generation of the K sound signal KA and the C sound signal KC. Fig. 6 is a flowchart showing the main measurement procedure of the first embodiment, Fig. 7 is a flowchart showing details of the timing process, and Fig. 8 shows the same noise removal effect with a simple hardware configuration. FIG. 9 is a block diagram of a digital blood pressure monitor according to a second embodiment of the invention, and FIG. 9 is an operation timing chart of the configuration shown in FIG. Here, 1...cuff, 2...C sound microphone (cuff side microphone), 3...K sound microphone, 4...pipe, 5...main body, 6...pressure sensor, 7...A/D converter, 8...pulse filter , 9, 12, 15... Comparator (COMP), 10, 13... Amplifier (AMP), 11
...K sound filter, 14...C sound filter, 16...Central processing unit (CPU), 17
. . . Display portion, 18 . . . Pressure contact surface.

Claims (1)

[Claims] 1. K worn with a cuff of inelastic structure interposed therebetween.
and a C-sound microphone; a pulse pressure detection means for detecting a pulse pressure component of the cuff pressure and outputting a pulse pressure signal; A signal corresponding to the Korotkoff sound is extracted from the output signal of the sound microphone and K
K sound detection means outputs as a sound signal; detects the pulse sound transmitted through the cuff and noise generated in the cuff with the C sound microphone, and detects the noise from the output signal of the C sound microphone; C that extracts the corresponding signal and outputs it as a C sound signal
A sound detection means; and a noise identification means for determining whether or not the K sound signal is noise based on the relationship between the generation time of the pulse pressure signal, the K sound signal, and the C sound signal. Features: Non-invasive digital blood pressure monitor. 2. Claim 1, wherein the C-sound detection means includes the C-sound microphone and a high-pass filter connected to the output side of the microphone for blocking sound signal components below a predetermined frequency. The non-invasive digital blood pressure monitor described. 3. The non-invasive digital sphygmomanometer according to claim 2, wherein the C-sound microphone and the K-sound microphone are superimposed with each other with a small distance therebetween. 4 The low cutoff frequency of the high pass filter is
The non-invasive digital blood pressure monitor according to claim 2, characterized in that the frequency is set to approximately 100Hz. 5. Claims 1 to 5, characterized in that the noise identification means recognizes the K sound signal as noise when the generation of the C sound signal is recognized within 20 ms before and after the generation of the K sound signal. 4. The non-invasive digital blood pressure monitor according to any one of Item 4.