JPH0759233B2 - Electronic blood pressure monitor - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electronic sphygmomanometer, and more particularly to an electronic sphygmomanometer that determines blood pressure based on Korotkoff sounds.

[Prior Art] Conventionally, in this type of electronic sphygmomanometer, the Korotkoff sound signal is gated by the pulse wave gate signal obtained by extracting the pulsating component of the cuff pressure to prevent erroneous determination due to noise or artifacts.

[Problems to be Solved by the Invention] However, for example, when the decreasing speed of the cuff pressure is high, a sufficient pulsating component cannot be extracted from the cuff pressure. As a result, the pulse wave gate signal could not be formed, and thus the detection of the important Korotkoff sound signal was lost, which often resulted in erroneous measurement.

The present invention eliminates the above-mentioned drawbacks of the prior art, and an object thereof is to provide an electronic sphygmomanometer capable of unique and accurate blood pressure determination based only on Korotkoff sound signals.

In order to achieve the above object, the electronic blood pressure monitor of the present invention has the following configuration. That is, [Means for Solving the Problem] In an electronic sphygmomanometer that determines blood pressure by Korotkoff sounds, a detection means for detecting Korotkoff sound signals and a plurality of consecutive time intervals during a predetermined time after the start of measurement. Window setting means for setting a window, and in each of the plurality of time windows, peak-bottom detecting means for detecting respective peak and bottom values of the detection signal by the detecting means, peak detected by the peak-bottom detecting means, and Setting means for setting the base noise level of the detection signal by the detecting means based on the difference value between the bottom values.

[Operation] In the above configuration, a plurality of time windows that are temporally continuous are set for a predetermined time after the start of measurement, and in each of the plurality of time windows, the detection signal of the detection signal of the Korotkoff sound is detected. Detect peak and bottom values. Then, the base noise level of the detection signal by the detecting means is set based on the difference value between the detected peak and bottom values.

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

FIG. 1 is a block diagram of the electronic sphygmomanometer of the embodiment, and FIG. 2 is an external view of the electronic sphygmomanometer of the embodiment. In the figure, this electronic sphygmomanometer includes a main body unit 10 for determining blood pressure, a pressurizing unit 40 for pressurizing / depressurizing a cuff, a K sound detecting unit 50 for detecting Korotkoff sound (K sound), and external charging. Consists of 60 vessels.

In the main body 10, 11 is a rechargeable battery, and as shown in FIG. 2, 4.8V is supplied by four series connection of 1.2V rechargeable batteries. A mounting portion 11a for the rechargeable battery 11 is provided on the main body portion 10 side, and a lid 11b is covered after the rechargeable battery 11 is mounted. Returning to FIG. 1, the rechargeable battery 11 can be charged by an external charger 60. 12 is a power control, and a power switch 13
The supply / cutoff of 4.8V to the main body unit 10 is controlled according to the operation of. Reference numeral 14 is a basic oscillator (X1), which generates a basic clock signal. A mode switch 15 is used to select a use mode of the electronic blood pressure monitor by operation. For example, the (A) mode is a mode for measuring a normal person. (B) mode is
It is a mode in which this device does not automatically measure blood pressure but functions as a mercury column in the conventional doctor's auscultation method.
Only the cuff pressure that changes sequentially is displayed. The mode (C) is a mode for measuring a person having an auscultation gap, and the timing for determining the disappearance time of the Korotkoff sound is extended.
Reference numeral 31 is a start switch, and the user can manually instruct measurement start.

A filter amplifier 16 filters and amplifies the Korotkoff sound (K sound) signal detected by the microphone 51. Reference numeral 17 is a reference power supply unit, which supplies a controlled and stabilized reference power supply, a reference voltage, etc. to an amplifier circuit and an A / D conversion unit that require a stabilized power supply. Reference numeral 18 is a pressure detection unit that detects the cuff pressure. An amplifier 19 amplifies the detected cuff pressure signal. Reference numeral 26 is an A / D converter, which samples the amplified cuff pressure signal and converts it into a digital signal. An external memory 25 temporarily stores various data required for blood pressure measurement. 28 is a normally open exhaust valve, which is closed by a drive signal from the drive unit 27.

Reference numeral 29 is a display (LCD), as shown in FIG. 2, which sequentially displays the cuff pressure during measurement, displays the determined systolic blood pressure SYS and diastolic blood pressure DIA, and a measuring means which gives these measurement results. Priority display, underpressure display, pulse rate, etc. area 29a, pulse wave signal amplitude graph display during measurement, cuff decompression speed range microcomputer display during measurement, sphygmomanometer An area 29b is provided for displaying the selected use mode, a rapid exhaust mark indicating that rapid exhaust is in progress, and the like. Returning to Figure 1, 3
0 is a buzzer that notifies the end of measurement.

Reference numeral 20 denotes a microprocessor unit (LSIC), which performs main control and processing of the main body unit 10. In the microprocessor unit 20, 21 is an A / D converter, which samples the amplified K sound signal and converts it into a digital signal. Reference numeral 22 denotes a control unit, which has a so-called CPU unit built-in, inputs sampled cuff pressure signals and K sound signals, exchanges processing data with an external memory 25, and displays via a display drive unit 24.
It controls the display of the LCD 29. Reference numeral 23 denotes a Korotkoff sound / pulse wave recognition unit, which executes the processing programs of FIGS. 3 to 10 described later together with the control unit 22.

In the pressurizing unit 40, 41 is a cuff wrapped around a person's upper arm, 42 is a constant speed (low speed) exhaust valve, 43 is a manual exhaust valve, 44 is a rubber ball, and 70 is a tube forming an air flow path. As shown in FIG. 2, the manual exhaust valve 43 includes a knob 43a for adjusting the low speed exhaust speed, and a fully open switch 43b for manually performing rapid exhaust.

FIG. 3 is a flow chart of the main process including the oscillometric measurement of the embodiment. In step S301, "pressurization detection" is performed.

This pressurization detection is performed, for example, by the method shown in FIG.
The horizontal axis of the figure is the time t, and the vertical axis is the cuff pressure P. Since the constant velocity exhaust valve 42 of this embodiment is always open and the exhaust valve 28 is normally open, when pressure is applied by the rubber ball 44, the cuff pressure detection signal PS is initially zero. , Pulsates up and down as shown in the figure in response to the pump operation by the rubber ball 44, and accordingly the respective bottom detection signals BM
The value of (i) also rises for a while. Therefore, the control unit 22
It is determined as "pressurization detection" by detecting that the content of BM (i) has increased n times (n = 3 or 4) consecutively.
FIG. 11B shows a case where the arm around the cuff 41 is simply moved without performing the pump operation with the rubber ball 44. In this case, each bottom detection signal BM (i) is continuously n
The pressure cannot be detected because the pressure cannot be raised once. The above details will be described later according to the flow chart of FIG.

Although the contents of the signal BM (i) are compared in this embodiment, the present invention is not limited to this. For example, peak detection signals PM (0), PM
(1), ... May be obtained and these may be compared.

Further, as shown in FIG. 11 (C), when the pressure route is tightly closed, the inflection points IP0 to IP6 can be detected. In this case, inflection points IP0, IP2, IP4, ... or inflection points IP1, IP3, IP5, ...
Etc. may be compared. The inflection point may be detected by detecting the rising gradient of the cuff pressure per unit time and obtaining the point where the gradient changes.

Returning to FIG. 3, in step S302, the exhaust valve 28 is closed. At step S303, the process waits for "pressurization stopped". That is, the operator operates the pump until the desired cuff pressure is reached, and the pressurization is stopped. Then, due to the action of the constant velocity exhaust valve 42, the cuff pressure is adjusted at that time (for example, 2 to 4 mmHg /
S) decrease. For example, as shown in FIG. 12, the control unit 22 determines that “pressurization is stopped” by detecting that the cuff pressure signal PS decreases at a constant speed for 0.5 seconds.

In step S304, measurement is started. By this measurement start, in addition to the oscillometric measurement after step S305, “K sound measurement with gate” and “K sound measurement without gate” described later are performed in parallel. In step S305, initial setting for oscillometric measurement is performed. That is, a flag UF for holding the rising of the cuff pressure signal PS, a flag UDF for holding the rising of the cuff pressure signal, a bottom counter BC for counting the number of times of bottom occurrence of the pulse wave signal component of the cuff pressure, and a K sound detection. All gate signals KG are reset. In step S306, "pulse wave detection" is performed.

This pulse wave detection is performed, for example, by the method shown in FIG. That is,
When the point at which the cuff pressure signal PS first rises is detected after the start of measurement, this is the start point of the first pulse wave signal component, and the bottom signal BM (0) at that time is stored. At the same time, the K sound gate KG for detecting Korotkoff sounds is opened. Next, the top (peak) of the cuff pressure signal PS is detected, the top signal TM (0) at that time is stored, and the bottom counter BC is +
Do 1 Next, the point where the cuff pressure signal PS becomes equal to the bottom signal BM (0) is detected, and the K sound gate KG is closed. The above is one cycle of pulse wave signal component detection, and the same pulse wave detection processing is repeated thereafter. The above details will be described later according to the flow chart of FIG.

Returning to FIG. 3, the bottom counter BC is set to 3 in step S307.
If it is not 3 or more, it is determined at step S309 whether the signal * END is true or not. * END is a signal that becomes true when both “K sound measurement with gate” and “K sound measurement without gate” are in the end state. Signal * at this point
Since END is not true, step S310 checks whether PS <20 mmHg. Here, 20 mmHg is the lowest cuff pressure at which blood pressure measurement can be performed. At this point, it is not PS <20 mmHg, so the process returns to step S306. Thus, if a plurality of pulse waves are detected and BC ≧ 3 is satisfied in step S307, the process proceeds to step S308 and BM (C-3) <BM (C-2) <BM (C-
1) Determine whether <BM (C). Here, (C) is the address of the external memory 25 indicated by the bottom counter BC. That is, in this process, the bottom signal BM (C-
The bottom signal BM (C) from 3) to the present time is examined,
If these are continuously rising, it means that the pressurization state by the rubber ball 44 was detected again during the measurement,
Control returns to step S303. If it is not continuously increased as determined in step S308, the process proceeds to step S309. Thus, at step S309, the signal * END is true, or at step S310
When PS <20 mmHg is discriminated in step S311, the "oscillometric analysis" is executed.

This oscillometric analysis is performed, for example, by the method shown in FIG. 13 (A). In the figure, when the cuff pressure PS starts to fall,
The pulse wave signal PA appears before the systolic blood pressure SYS, reaches the maximum value PAmax (mean blood pressure) at the position of ⊚, and then temporarily decreases toward the diastolic blood pressure DIA. The control unit 22 checks the pulse wave signal PA stored in the external memory 25 in advance, first detects the maximum value PAmax, and before this, the pulse wave signal P
Immediately before the amplitude of the pulse wave signal PA falls below the threshold TH2 = 0.8 × PAmax after the maximum value PAmax is determined with the cuff pressure PS when the amplitude of A exceeds the threshold TH1 = 0.5 × PAmax. Determine the lowest blood pressure DIA with the cuff pressure PS at the time point of. In addition, SYS, DIA of this embodiment
There is a feature in the determination method of, and its details will be described later according to the flow chart of FIG.

Returning to FIG. 3, the buzzer sounds at step S312, and the exhaust valve 28 is opened at step S313, and the measurement is completed.

In the above, the display of the results by each measurement method is given a priority, and for example, the priority is low in the order of “K sound measurement with gate”, “Oscillometric measurement”, and “K sound measurement without gate”. I'm running. Therefore, normally, the result of the K-tone measurement with gate is preferentially displayed. However, by pressing the mode switch 15, the result of the oscillometric measurement or the gateless K sound measurement can be preferentially displayed in advance. Alternatively, after the measurement is completed, it is possible to simply change the display to arbitrarily select these measurement results.

In the present embodiment, the rate of decrease of the cuff pressure can be adjusted, and when the rate of decrease of the cuff pressure is high, it becomes difficult to extract the pulse wave true PA, which hinders the oscillometric measurement and the K sound measurement with the gate. May come. However, even in such a case, according to the present embodiment, since the gateless K sound measurement is performed, an accurate measurement result can be obtained.

FIG. 4 is a flow chart showing details of pressurization detection in the embodiment. In step S401, UF, UDF, BC are cleared, and the register PR that holds the sampled cuff pressure signal PS
To clear. In step S402, the cuff pressure signal PS is sampled. This sampling may be, for example, 32 mS cycle. In step S403, (PR + ΔP) −PS is calculated. Here, ΔP gives a small threshold value. (PR + Δ
If P) -PS≥0, the process proceeds to step S406, where (PR-Δ
P) -PS is calculated. When (PR−ΔP) −PS ≦ 0, PS is
Since it is in the range of ± ΔP compared to PR (0 at the beginning), nothing is done and the process returns to step S402.

When (PR + ΔP) −PS <0 in the calculation of step S403, the cuff pressure PS is found to increase by the threshold value ΔP or more, so the process proceeds to step S404 and UF is checked. Until now, the cuff pressure has continued to drop at a constant level, so UF = 0 at this point. Control proceeds to step S410, where UF is set and UDF is reset. That is, the cuff pressure starts to increase. External memory 25 bottom memory for step S411
Store the contents of PR in BM (C). Here, (C) is an address indicated by the bottom counter BC. BC in step S412
= 3 is determined. Since BC = 0 at the beginning, the process proceeds to step S405, and the contents of PR are updated with the contents of PS. Thus, while PS continues to rise, steps S402, S403, S4
04, loop S405.

If (PR−ΔP) −PS> 0 in the calculation of step S406,
Since a decrease of not less than the threshold value ΔP is recognized, the process proceeds to step S407 and UF is checked. Since UF = 1 here, proceed to step S408 to reset UF and set UDF. The descent starts after the cuff pressure rises. In step S409, the bottom counter BC is incremented by 1.

In this way, when BC = 3 is determined in step S412 while the pulsating rise due to the pressurization operation by the rubber ball 44 is detected, the process proceeds to step S413, and BM (0) <BM (1) <BM.
(2) <BM (3) is determined. If YES, it means “pressurization detection”, so the process is exited. If NO, BM (0) ← BM (1) ← BM (2) ← BM (3) is downshifted in step S414, and the bottom counter BC is decremented by 1 in step S415. Thus, thereafter, it is determined whether or not the pressurization is detected every time the bottom BM is detected.

FIG. 5 is a flow chart of pulse wave detection of the embodiment. This process is similar to the pressure detection process of FIG. 4 except for a part. The initial setting is performed in step S305 in FIG. In step S501, the cuff pressure signal PS is sampled and the step
In S502, check the UDF. Since UDF = 0 at the beginning, the flow advances to step S505 to calculate (PR + ΔP) -PS. (PR +
When ΔP) -PS ≧ 0, step S510 (PR-ΔP) -PS
Is calculated. When (PR−ΔP) −PS ≦ 0, the sampled cuff pressure PS is in the range of ± ΔP compared to the contents of the register PR (here, the previous value is held), so nothing is done. Then, return to step S501.

When (PR-.DELTA.P) -PS> 0 in the calculation of step S510, the cuff pressure PS is recognized to fall below the threshold value .DELTA.P. Control proceeds to step S511 to check UF. At the start of measurement, the cuff pressure was originally falling, so UF = 0.
Control proceeds to step S515, where the contents of register PR are simply PS
Update with the contents of.

When (PR + ΔP) −PS <0 in the calculation of step S505, the cuff pressure PS is recognized to rise above the threshold value ΔP. Control proceeds to step S506, where UF is examined. If UF = 0, it means that the rise is detected from the fall of the cuff pressure, so step S507
Go to to reset UF and reset UDF. Step S
At 508, the contents of PR are stored in the bottom memory BM (C).
At step S509, the gate signal KG for K sound detection is opened. After that, while the cuff pressure PS continues to rise, the step S505,50
Loop through 6,515 routes.

When (PR-.DELTA.P) -PS> 0 in the calculation of step S510, the cuff pressure is recognized to fall below the threshold value .DELTA.P. Control proceeds to step S511 to check UF. This time UF = 1, so go to step S512 to reset UF and set UDF. After the cuff pressure rises, it begins to fall. Step S5
At 13, the contents of PR are stored in the top memory TM (C). In step S514, the bottom counter BC is incremented by 1.

When UDF = 1, that is, when the fall start after the increase of the cuff pressure is detected, the determination in step S502 is YES, the control proceeds to step S503, and it is determined whether PS <BM (C-1). PS
If <BM (C-1), the process proceeds to step S504 to close the K sound detecting gate signal KG.

Thus, the external memory 25 stores the number of data BM (C) and TM (C) necessary for the subsequent oscillometric analysis,
At the same time, a gate signal KG for K sound detection is generated in real time.

FIG. 6 is a flow chart of the oscillometric analysis of the embodiment. In step S601, data BM (C) and TM
The pulse wave signal PA is obtained from (C). In FIG. 12, when the decompression rate of the cuff at that time is −KmmHg / s, for example, the amplitude of the pulse wave signal PA3 is {TM (3) −BM (3) + KΔ.
t}. Here, Δt is the time from BM (C) to TM (C). Similarly, the amplitude PAn is calculated for other pulse wave signals. At step S602, PAmax is detected.
In Fig. 13 (A), PAmax is the amplitude P of the pulse wave signal.
A is the largest. PAmax can be easily detected by checking the amplitude PA of the pulse wave signal from the young address of the external memory 25.
In step S603, systolic blood pressure SYS is determined. There are two methods for determining the systolic blood pressure SYS in this embodiment.

FIG. 13 (B) is a diagram for explaining the first method of determining the systolic blood pressure SYS. The first method is to read the amplitude PA of the pulse wave signal in the external memory 25 from a young address.
If the threshold value TH1 = 0.5 × PAmax, the pulse wave signal exceeding the threshold value TH1 is first detected. When the amplitude PA3 of the next pulse wave signal exceeds the threshold value (PA2-C4), the systolic blood pressure SYS is determined using the cuff pressure PS corresponding to the pulse wave signal. Here, C4 is a fourth predetermined value, which is statistically determined in advance based on the variation in the amplitude PA of the actual pulse wave signal. If the amplitude PA3 of the pulse wave signal does not exceed (PA2-C4), confirm that the amplitude PA4 of the next pulse wave signal exceeds the threshold TH1. When the difference in amplitude is obtained and the difference is equal to or greater than the fifth predetermined value C5,
The systolic blood pressure SYS is determined by using the cuff pressure PS corresponding to the pulse wave signal. Similarly, the fifth predetermined value C5 is also statistically determined in advance based on the variation in the amplitude of the actual pulse wave signal PA.

That is, the amplitude PA3 of the pulse wave signal does not exceed (PA2-C4), the amplitude PA4 of the next pulse wave signal exceeds the threshold TH1, and the amplitude difference between the pulse wave signal and the pulse wave signal is the first. 5
When the pulse wave signal is greater than or equal to the predetermined value C5, the pulse wave signal is determined as noise. On the other hand, when the amplitude PA3 of the pulse wave signal does not exceed (PA2-C4) and the amplitude PA4 of the next pulse wave signal does not exceed the threshold TH1, or the difference between the amplitudes of the pulse wave signal and the pulse wave signal is the fifth. When it is less than the predetermined value C5 of, the pulse wave signal is determined to be noise.

Thus, although it frequently occurs in practice, the systolic blood pressure SYS can be reliably determined even if the amplitude PA of the pulse wave signal varies.

FIG. 13 (C) is a diagram for explaining the second method of determining the systolic blood pressure SYS. The second method is to read the amplitude PA of the pulse wave signal in the external memory 25 from the position of PAmax toward a young address. Similarly, threshold TH1 = 0.5 x PAma
When x is set, first, a pulse wave signal below the threshold TH1 is detected. Then, the amplitude PA2 of the next pulse wave signal becomes the threshold value (PA3
+ C6) is not exceeded, the cuff pressure PS corresponding to the pulse wave signal
Therefore, the systolic blood pressure SYS is determined. Here, C6 is a sixth predetermined value, which is statistically determined in advance based on the variation in the amplitude PA of the actual pulse wave signal. Also, the amplitude PA of the pulse wave signal
When 2 exceeds the threshold (PA3 + C6), the pulse wave signal amplitude PA
When 1 is TH1 or less, the difference in amplitude between the pulse wave signal and the pulse wave signal is obtained, and when the difference is the seventh predetermined value C7 or more, the cuff pressure PS corresponding to the pulse wave signal is less than About systolic blood pressure
Judge as SYS. Similarly, the seventh predetermined value C7 is also statistically determined in advance based on the variation in the amplitude PA of the actual pulse wave signal.

That is, even if the amplitude PA2 of the pulse wave signal exceeds the threshold value (PA3 + C6), the amplitude PA1 of the pulse wave signal is TH1 or less, and the amplitude difference between the pulse wave signal and the pulse wave signal is the seventh predetermined value C7 or more. When, the pulse wave signal is determined to be noise. On the other hand, when the amplitude PA2 of the pulse wave signal exceeds the threshold value (PA3 + C6) and the pulse wave signal is TH1 or more, or when the amplitude difference between the pulse wave signal and the pulse wave signal is less than the seventh predetermined value C7. Determines that the pulse wave signal is noise.

Thus, the accurate systolic blood pressure SYS can be determined even if the amplitude PA of the pulse wave signal varies, and since the external memory 25 can be traced back from the position where PAmax is detected, the pulse wave signal data read control is simple. .

Returning to FIG. 6, in step S604, the diastolic blood pressure DIA is determined.

FIG. 13 (D) is a diagram illustrating a method of determining the diastolic blood pressure DIA according to the embodiment. In this method, the amplitude PA of the pulse wave signal in the external memory 25 is read back from the position of PAmax. If the threshold TH2 = 0.8 x PAmax, the threshold T
Detect pulse wave signals below H2. When the amplitude of the next pulse wave signal does not exceed the threshold value (PA6 + C8), the cuff pressure PS corresponding to the pulse wave signal is used to determine the diastolic blood pressure DIA. Here, C8 is an eighth predetermined value, which is statistically determined in advance based on the variation in the amplitude PA of the actual pulse wave signal. When the amplitude PA7 of the pulse wave signal exceeds the threshold value (PA6 + C8) and the pulse wave signal is TH2 or less, the difference between the pulse wave signal and the pulse wave signal is calculated, and the difference is the ninth predetermined value. When C9 or more, the cuff pressure PS corresponding to the pulse wave signal is used to determine the diastolic blood pressure DIA. Similarly, the ninth predetermined value C9 is also statistically determined in advance based on the variation in the amplitude of the actual pulse wave signal PA.

That is, when the amplitude PA7 of the pulse wave signal exceeds the threshold value (PA6 + C8) and the pulse wave signal is TH2 or more, or when the difference between the pulse wave signal and the pulse wave signal is less than the ninth predetermined value C9, the pulse wave Judge the signal as noise. On the other hand, the amplitude PA7 of the pulse wave signal exceeds the threshold value (PA6 + C8), and the pulse wave signal becomes TH2.
Hereinafter, when the difference between the pulse wave signals is greater than or equal to the ninth predetermined value C9, the pulse wave signal is determined to be noise.

Thus, an accurate diastolic blood pressure DIA can be determined even if the amplitude of the pulse wave signal PA varies, and the same determination algorithm as the second determination method of the systolic blood pressure SYS described in FIG. 13 (C) is used. Therefore, the programs can be standardized and simplified.

FIG. 12 is a diagram for explaining the K-tone measurement with a gate according to the embodiment. The gated K sound measurement is to determine the systolic blood pressure SYS and the diastolic blood pressure DIA based on the appearance and disappearance of the Korotkoff sound gated by the gate signal KG.

It is known to measure Korotkoff sound in the gate for K sound. Further, the part that determines the onset and disappearance of the Korotkoff sound, which is a characteristic part of the present embodiment, is the same as in the gateless K sound measurement described later, and thus the description thereof is omitted.

FIG. 7 is a flow chart for K-tone measurement without a gate according to the embodiment. Initial settings are made in step S701. That is, a register BN that stores the magnitude of the base noise (BN), a flag 2ndF that holds that the first K sound has been detected, a flag DIAF that indicates that the control is in the detection process of the diastolic blood pressure DIA, and this gate is not present. Flag KE indicating that K sound measurement is completed
Reset each NDF. In step S702, base noise detection "BN detection" is performed. In the gateless K sound measurement, the gate signal KG for K sound detection is not used, so noise and Korotkoff sounds must be distinguished by unique processing. Therefore, it is necessary to detect BN in the initial stage of measurement.

This BN detection is performed, for example, by the method shown in FIG. In the figure, the 2 seconds after the start of measurement is divided into 16 equal parts, each 125 mS window is set, and the noise level in each window is measured.

The noise level in this window can be measured, for example, with the 14th
The method shown in the figure is used. The vertical axis of the figure is the 8-bit A / D conversion output, and the K sound signal KS changes within the range of A / D conversion output level 0-255. The horizontal axis represents time t, and when measuring within the window, the noise level is measured within the section of t = 0 to 125 mS. The K sound signal KS observed in each window is a signal having various amplitudes pulsating around the substantially central portion of the vertical axis. Therefore, the peak and the bottom in the window are detected, the respective values are stored in the peak register KP and the bottom register KB, and the difference (KP-KB) between these values is obtained and set as the noise level in the window. When the initial pressure of the cuff 41 is not sufficient, Korotkoff sound may be included in the window as shown in the figure.

Returning to FIG. 15, the area counter AC is + for each window.
It is counted as 1 and counts 0 to 15. The control is AC = 0.
About each window of 1 (KP0, KB0), (KP1, KB
1) detects and stores the peak memory P ₀ of connexion window 0 preparative KP0 and larger KP1 of them, also KB0 and K
Taken the smaller B1 and stores it in the bottom memory B ₀ of go-between window 0. Next, the control detects (KP1, KB1), (KP2, KB2) for each window of AC = 1, 2 and
KP1 and stored larger peak memory P ₁ of connexion window 1 preparative of KP2, also stored in the bottom memory B ₁ of connexion window 1 preparative smaller KB1 and KB2. And so on
Get up to P ₁₅ , B ₁₅ . Then, the differences (P ₁ −B ₁ ), (P ₂ −B ₂ ), ..., (P ₁₅ −B ₁₅ ) are obtained for each of these 15 pairs, and the minimum one of the 15 differences is taken. Base noise BN. The above details will be described later with reference to the flow charts of FIGS. 8 and 9.

The method of determining the base noise BN is not limited to this. The base noise BN may be, for example, an average value of 15 differences. Further, it is also possible to use an average value of n extracted from the smaller of 15 differences.

Returning to FIG. 7, in step S703, the counter SC that determines the determination timing of the systolic blood pressure SYS and the register T that determines the determination timing of the disappearance of the Korotkoff sound are respectively cleared, and the register THK that holds the threshold for the Korotkoff sound is used to determine the systolic blood pressure. Threshold value BN + C1 (for example, 100 mmHg) is set. Here, BN is the base noise detected in step S702.
BN and C1 is a first predetermined value. In step S704, the registers KP and KB, the control flag RSKF for initializing the K message detection processing described later, and the timer t are reset. In step S705, K sound sampling interrupt (KSIN
T) is enabled. The control advances to step S706 and stands by (executes IDLE).

FIG. 10 is a flow chart of the K sound sampling interrupt processing of the embodiment. In step S1001, the K sound signal KS is sampled, and in step S1002, the control flag RSKF is checked. Since RSKF = 0 at the beginning, the flow advances to step S1003 to check the contents of the timer t. Since t = 0 at the beginning, the K sound signal KS sampled in the registers KP and KB is set in step S1008. Initialization of registers KP and KB. In step S1006, the timer t is + Δt
(For example, if the sampling cycle is 1 mS, Δt = 1 mS).

If t = 0 is not found in step S1003, the operation proceeds to step S1004 to perform calculation (KP-KS). (KP-KS) <
When it is 0, an increase in KS with respect to KP is recognized, so the flow advances to step S1005 to update the contents of KP with the contents of KS. When (KP-KS) ≧ 0, no increase in KS with respect to KP is recognized, and therefore the process proceeds to step S1009 to perform calculation (KB-KS). When (KP-KS) ≤0, the decrease of KS with respect to KB is not recognized, so the timer t is simply updated. But (KB
When −KS)> 0, a decrease in KS with respect to KB is recognized, so the flow advances to step S1010 to update the contents of KB with the contents of KS. Thus, the content of the register KP or KB is updated every time the K sound signal KS is sampled.

Returning to FIG. 7, when the K sound sampling interrupt processing is completed, the input is made to step S707. Here, KSINT is disabled to prevent duplicate interrupts. In step S708, it is determined whether or not (KP-KB) ≧ THK. If YES, the first Korotkoff sound is detected, so the flow proceeds to step S709, and the flag 2ndF is checked. 2n because it is the first Korotkoff sound
Since dF = 0, the control advances to step S711, and 1 is set in 2ndF. In step S712, the cuff pressure PS at that time is saved in the external memory 25. Check DIAF in step S713. DIAF ＝ because it is not yet the measurement process of diastolic blood pressure DIA
0, and the control advances to step S715 to increment the counter SC by 1. In step S716, the counter SC is checked. Since SC = 1 here, the process returns to step S704. Step
In S704, register to detect the next Korotkoff sound.
KP, KB, timer t, etc. are reset.

When the next Korotkoff sound is detected in step S708, the process proceeds to step S709, and this time 2ndF = 1. Control is step
Proceed to S710, and check whether t ≧ 0.3S. According to medical statistics, the next Korotkoff sound does not occur within 0.3 seconds after the previous Korotkoff sound was generated. Therefore, the K sound signal in this section is ignored to prevent erroneous determination due to noise. Therefore, when the determination of step S710 is NO,
In step S714, the control flag RSKF is set to 1.

Returning to FIG. 10, when RSKF = 1 in the determination of step S1002, the process proceeds to step S1007, and RSKF is reset. In step S1008, K sampled in registers KP and KB
Set sound signal KS. Thus, KP and KB so far
The contents of the are canceled, and the detection of Korotkoff sounds is restarted.

Returning to FIG. 7, when it is determined in step S710 that t ≧ 0.3S,
It is a regular Korotkoff sound detection. Control is step S71
Proceed to 2, S713, S715, S716. Since SC = 2 this time, proceed to step S717 and set 1 to DIAF. Step S7
In step 18, the threshold THN for determining the minimum blood pressure is set in the register THK BN + C2. Here, C2 is a second predetermined value. Step
In S719, if the display priority allows,
The first cuff pressure value PS saved in step S712 is displayed in the systolic blood pressure SYS portion of the display LCD29. After that, diastolic blood pressure DI
This is the process of detecting A.

If NO in step S708, the process proceeds to step S720 to determine whether t = 2S. According to medical statistics, it is considered that the second Korotkoff sound generation is limited within 2 seconds from the previous Korotkoff sound generation. Therefore, the process returns to step S705 until t = 2S, and waits for the generation of Korotkoff sound. However, if Korotkoff sound does not occur even when t = 2S,
Proceed to step S721 and check DIAF. If DIAF = 0, return to step S705. Such a case can occur between the start of measurement and the detection of the first Korotkoff sound. Since DIAF = 1 now, the process proceeds to step S722, and the register T is incremented by + t. In the first case, T = 2S. In step S723, it is checked whether T> n beats. Here, in the case of (A) mode measurement, it is desired to detect that two Korotkoff sounds are missing. However, since the cycle of one Korotkoff sound differs depending on the subject, a process (not shown) is performed in advance. Then, the cycle of one Korotkoff sound is obtained, and in step S723, it is checked whether or not T> (cycle of 2 × 1 beat). Also, in the case of (C) mode measurement for a person with an auscultation gap, it is detected that Korotkoff sound is missing for 5 beats, so in step S723, it is checked whether T> (5 × 1 beat cycle). . In any case, if the subject's one-beat cycle is relatively long (for example, about 2 seconds), the process of step S722 is performed multiple times, and in the case of the second time, T = 4S and the third time. In this case, T = 6S. Thus, if the determination in step S723 is YES, the process proceeds to step S724, and if the display priority allows it, the indicator
The last cuff pressure value PS saved in step S712 is displayed on the diastolic blood pressure DIA part of the LCD 29. In step S725, 1 is set to the measurement end flag KENDF of the K sound without gate.

FIG. 8 is a BN detection flow chart of the example. In step S801, the area counter AC is cleared. Step
In S802, the contents of the registers KP and KB and the timer t are cleared. Step S803 enables KSINT,
At 804, it stands by (executes IDLE).

When the K sound signal KS is sampled according to the processing of FIG. 10 in the same manner as described above, the control is performed in step S805 of FIG.
To enter. In this case, KSINT is disabled, the process proceeds to step S806, and it is determined whether t = 125 mS. t = 125mS
Until it becomes, the control is returned to step S803 because it is within one window. When t = 125 mS, the process proceeds to step S807 to detect area noise (AN detection).

FIG. 9 is a flow chart for AN detection according to the embodiment. In step S901, the contents of the area counter AC are checked. Initially
Since AC = 0, the process proceeds to step S911 and the register P _A ,
The contents of registers KP and KB are set in B _A respectively.

Returning to FIG. 8, in step S808, the area counter AC is checked. AC = 15 yet, so add AC to step S814
Then go back to step S802.

Returning to FIG. 9, the next time the processing is input, AC = 1. Control proceeds to step S904, the register P _B, to B _B respectively register KP, the contents of the KB to excisional. With this, AC = 0
The peak bottoms P _A , B _A of AC and the peak bottoms P _B , B _{B of} AC = 1 were aligned. In step S905, calculation (P _A -P _B ) is performed,
When (P _A -P _B ) <0, P _B is high, so the flow advances to step S907 to set the contents of P _{B in} P (C) of the external memory 25.
Here, (C) is an address indicated by the area counter AC. When (P _A −P _B ) ≧ 0, P _A is high, so the step
In S906, the contents of P _A are set in P (C). Similarly, in step S908, calculation (B _A −B _B ) is performed and (B _A −
If B _B )> 0, B _B is low, so the flow advances to step S910 to set the contents of B _B to B (C) of the external memory 25. When (B _A −B _B ) ≦ 0, B _A is low, so the flow advances to step S909 to set the contents of B _{A in} B (C).

Thus, the next time you enter this process, the AC will be greater than or equal to 2. The control proceeds to step S903 to shift the contents of the registers P _B and B _B into the registers P _A and B _A , respectively. Step S904 the register P _B, respectively register KP to _B B, the contents of the KB to excisional. Now, with AC = 1 peak bottoms P _A and B _A
The peak bottoms P _B and B _{B of} AC = 2 were lined up. Hereinafter, the area noises P (15) and B (15) are similarly detected.

Returning to FIG. 8, when AC = 15 is determined in step S808, the flow advances to step S809 to set the base noise BN to the minimum value of (P _j −B _j ). This is the detected base noise
It is BN. Here, j is 0 to 15. In step S810 that exceeds (P _j -B _j) of (BN + C3) whether to determine certain. Here, C3 is a third predetermined value, for example (BN
+ C3) = 100 mmHg. If the determination is NO, the process ends. If YES, it means that there is a signal corresponding to the Korotkoff sound during the detection of the base noise, and the initial pressurization by the rubber ball 44 is insufficient. The control proceeds to step S811, and the systolic blood pressure SYS can no longer be measured. Therefore, set 1 to DIAF, and further proceed to step S812 to display LCD2.
“−−−−−” is displayed preferentially on the display of systolic blood pressure SYS of 9
Is displayed. In this case, in the process of FIG. 7, DIAF = 1 is input to step S703, but if the measurement is continued as it is, the measurement of systolic blood pressure SYS can be ignored and only measurement of diastolic blood pressure DIA can be performed. it can. Further, as described above, the user can re-pressurize during the measurement.

[Effects of the Invention] As described above, according to the present invention, a true Korotkoff sound signal and noise can be distinguished based on only Korotkoff sound signal, and unique accurate blood pressure determination can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram of an electronic blood pressure monitor of the embodiment, FIG. 2 is an external view of the electronic blood pressure monitor of the embodiment, FIG. 3 is a flow chart of a main process including oscillometric measurement of the embodiment, and FIG. FIG. 5 is a flow chart showing details of pressurization detection of the embodiment, FIG. 5 is a flow chart of pulse wave detection of the embodiment, FIG. 6 is a flow chart of oscillometric analysis of the embodiment, and FIG. FIG. 8 is a flow chart for measuring the K sound without gate, FIG. 8 is a flow chart for detecting BN in the embodiment, FIG. 9 is a flow chart for detecting AN in the embodiment, and FIG. 10 is a flow chart for sampling K sound in the embodiment. Flow chart, FIGS. 11 (A) to 11 (C) are views for explaining the method of detecting pressure in the embodiment, and FIG. 12 is a view for explaining the method of detecting pulse wave and measuring K sound with gate in the embodiment, 13 (A) to (D) are oscillometric analysis of Examples. Description figures, FIG. 14 is a diagram illustrating a method of measuring the noise level in the window embodiment, FIG. 15 is a diagram illustrating a method of the base noise (BN) Detection Example. In the figure, 10 ... Main body part, 11 ... Rechargeable battery, 12 ... Power supply control, 13 ... Power supply switch, 14 ... Reference oscillation part, 15 ... Mode switch, 16 ... Filter amplifier, 17 ... Reference power supply part, 18 ... Pressure detection part , 19 ... Amplifier, 20 ... Microprocessor part (LS
IC), 21 ... A / D conversion section, 22 ... control section, 23 ... Korotkoff sound / pulse wave recognition section, 24 ... display drive section, 25 ... external memory, 26 ...
A / D converter, 27 ... Drive, 28 ... Exhaust valve, 29 ... Display (LCD), 30 ... Buzzer, 31 ... Start switch, 40 ... Pressure, 41 ... Cuff, 42 ... Constant speed (low speed) Exhaust valve, 43 ... Manual exhaust valve, 43a ... Knob, 43b ... Fully open switch, 44 ...
A rubber ball, 51 ... Microphone, 60 ... Charger, 70 ... Tube.

Claims (1)

[Claims] 1. An electronic sphygmomanometer for determining blood pressure based on Korotkoff sounds, detection means for detecting Korotkoff sound signals, and window setting for setting a plurality of time windows continuous in time for a predetermined time after the start of measurement. Means, and in each of the plurality of time windows, a peak-bottom detection means for detecting respective peak and bottom values of the detection signal by the detection means, and a difference between respective peak and bottom values detected by the peak-bottom detection means An electronic sphygmomanometer comprising: setting means for setting the base noise level of the detection signal by the detecting means based on the value.