JP2855767B2 - Electronic sphygmomanometer - Google Patents

Description

The present invention relates to an electronic sphygmomanometer that can determine a blood pressure value in a short time using fuzzy logic.

(B) Conventional technology As a conventional electronic sphygmomanometer, there is known an electronic sphygmomanometer in which a cuff is wound around an upper arm or the like (Rivaloch method). This electronic sphygmomanometer changes air pressure in the cuff (hereinafter simply referred to as cuff pressure) at a predetermined speed, detects cardiovascular information (pulse wave, Korotkoff sound, etc.) generated in the process of this change, and detects systolic pressure and diastolic pressure. Determine the period pressure (so-called systolic blood pressure, diastolic blood pressure).

In the above-mentioned conventional electronic blood pressure monitor, the cuff pressure needs to be changed over a range from the systolic pressure to the diastolic pressure, so that the measuring time ranges from several tens of seconds to one minute or more, and takes a long time, There is a problem that it is not possible to catch the rapid fluctuation of the information and to cause pain for the user.

Further, in the above-mentioned conventional electronic sphygmomanometer, the pressure of the cuff is insufficient and the blood pressure cannot be determined if the initial cuff pressure is low. In particular, it is difficult to detect insufficient pressurization during measurement with an electronic sphygmomanometer that uses a pulse wave as cardiovascular information (so-called oscillometric method). There was a problem that the measurement had to be repeated again.

Therefore, the applicant of the present application has solved the above problem,
An electronic sphygmomanometer to which fuzzy logic is applied has already been filed. The electronic sphygmomanometer according to the prior application focuses on the fact that the waveform of a pulse wave changes depending on a cuff pressure level based on a systolic pressure or a diastolic pressure (hereinafter referred to as a relative cuff pressure), The relative cuff pressure is estimated from the pulse waveform.

In order to evaluate the pulse wave waveform, for example, waveform parameters such as a pulse wave amplitude AMP, a pulse wave integration level RAV, and a waveform width ratio WID refractive index CON are used. Considering now the pulse wave amplitude AMP, FIG. 9 (a) shows the pulse wave amplitude AMP and relative cuff pressure (systolic pressure P _SYS standard) obtained for many subjects.
This is a dot plot of the relationship of P _C ′. This ninth
FIG. 7A shows a probability density distribution in which the pulse wave oscillation AMP and the relative cuff pressure P _C ′ are variable, and a membership function can be generated using the probability density distribution.

If the pulse wave amplitude AMP is actually measured, when the established density distribution shown in FIG. 9A is cut by the pulse wave amplitude AMP ^* , the cut is as shown in FIG. 1A. Wave amplitude AMP ^*
Membership function with relative cuff pressure as a variable for
Can be P _amp . Such a membership function can be obtained for other parameters by cutting each of the probability density distributions with the actual measurement values RAV ^* , WID ^* , and CON ^* [(b) (c) ( d), FIG. 9 (b)
(See (c) and (d)).

The membership functions P _amp , _Prav ,
A function P obtained by performing a predetermined logical calculation such as multiplication or addition on P _wid and P _con is as shown in FIG. 1 (e), for example, and corresponds to the maximum value P _max of this function P. Relative cuff pressure P _c ′
_* Can be presumed to be the most likely. If the relative cuff pressure P _c ′ _* can be estimated, this relative cuff pressure
The systolic or diastolic pressure can be easily calculated using P _c ′ _* and the current cuff pressure.

In the electronic sphygmomanometer according to the prior application, the probability density distribution for each parameter is stored in the memory as data in the form of a discretized matrix, and the pulse wave parameter is calculated from the actually detected pulse wave, Select the membership function for each parameter from the data in memory,
A predetermined logic operation is performed on the selected membership function to determine a blood pressure value. In order to calculate the pulse wave parameter, in principle, only one pulse wave needs to be detected, so that the measurement time can be shortened and the measurement can be performed quickly. In order to detect a pulse wave, it is necessary to pressurize the cuff, but the pressure only needs to be a value at which the pulse wave can be detected.

(C) Problems to be Solved by the Invention In the electronic sphygmomanometer according to the above-mentioned prior application, the function P obtained as a result of the logical calculation should always increase near the actual relative cuff pressure, but sometimes increases from there. Deviated relative cuff pressure
Also at P _c ′ ₊ , a large maximum point may occur as shown by a broken line (see FIG. 1 (e)). This may occur, for example, when pressure noise or the like is mixed during the measurement to disturb the pulse waveform and some waveform parameters are affected. In such a case, when the blood pressure value is determined using the relative cuff pressure _{Pc +} , a large error occurs.

The present invention has been made in view of the above, and an object of the present invention is to provide an electronic sphygmomanometer that can accurately determine a blood pressure value even when a pulse wave waveform is disturbed.

(D) Means for Solving the Problems In order to solve the above problems, an electronic sphygmomanometer according to the present invention includes: a cuff to be mounted on a subject; a pressurizing unit configured to pressurize air in the cuff to a predetermined pressure; Exhaust means for exhausting air in the cuff, pressure detecting means for detecting air pressure in the cuff, pulse wave detecting means for detecting a pulse wave of the subject, and a pulse wave detected by the pulse wave detecting means. A pulse wave parameter calculating means for calculating a plurality of parameters representing the pulse wave waveform, and for each of these parameters, a membership function for varying each parameter and the relative pressure of the air pressure in the cuff to the blood pressure value. Storing the membership function storing means, and the membership function corresponding to each parameter calculated by the pulse wave parameter calculating means, A membership function selecting means for selecting each from the membership functions stored in the storage means; and a membership function for each parameter selected by the membership function selecting means, performing a predetermined logical calculation to perform the relative pressure calculation. An electronic sphygmomanometer comprising: a blood pressure value determining unit that estimates a blood pressure value by estimating the relative pressure. The membership function storage unit stores an estimated range limited membership function that limits an estimated range of the relative pressure. The blood pressure value determining means estimates the relative pressure by using the estimated range limited membership function in addition to the selected member sheep function.

(E) Action In a living body, the systolic pressure is usually in the range of 50 mmHg to 260 mmHg (physiological range). Therefore, a membership function that limits the relative cuff pressure within this physiological range, for example, a membership function that is zero outside the physiological range, is used together with the membership function for each parameter, and is subjected to logical calculation to be estimated. The relative cuff pressure falls within the physiological range. Therefore, even if the pulse wave waveform is disturbed due to the mixing of pressure noise or the like, the determined blood pressure value can be prevented from being outside the physiological range.

(F) Embodiment One embodiment of the present invention will be described below with reference to the drawings.

FIG. 5 is a block diagram illustrating the configuration of the electronic blood pressure monitor of this embodiment. Reference numeral 2 denotes a cuff to be attached to the upper arm of the subject. The cuff 2 is connected to an exhaust valve 3, a pressurizing pump (pressurizing means) 4, and a pressure sensor (pressure detecting means) 5. The exhaust valve 3 and the pressure pump 4 are controlled by the MPU 10. After an output signal of the pressure sensor 4 (hereinafter referred to as a cuff pressure signal) is amplified by an amplifier 6, one of the output signals is directly input to an analog / digital (A / D) converter 8 to be digitally converted and taken into the MPU 10. . On the other hand, the cuff pressure signal is input to the band pass filter 7 and a pulse wave signal is detected. This pulse wave signal is also digitally converted by the A / D converter 8 and taken into the MPU 10.

The MPU 10 determines a blood pressure value by performing a logical operation on a function of calculating a parameter of a pulse waveform, a function of selecting a membership function based on the calculated parameter, and a selected membership function and an estimated range limited membership function. Function.

In the memory 10a in the MPU 10, a data table of the membership function and an operation program are stored. The display unit 9 is connected to the MPU 10, and the determined blood pressure value and the like are displayed.

Next, FIG. 3 and FIG.
This will be described below with reference to the drawings.

First, the cuff 2 is wrapped around the upper arm of the subject to start blood pressure measurement. First, the MPU 10 closes the exhaust valve 3 (step (hereinafter referred to as ST) 1; see FIG. 6), and turns on the pressurizing pump 4 (ST2). MPU10 takes in the cuff pressure signal from the A / D converter 8 (ST3), determines whether the current cuff pressure reaches a predetermined pressure P _co (ST4). This judgment
If NO, the process branches to ST3, and if YES, the process branches to ST5. That is, until the current cuff pressure reaches the set value P _co, processing of ST3, ST4 is repeated. This set value P _co is
Desirably lower than systolic pressure and higher than diastolic pressure,
There is no need to set it strictly.

In ST5, the MPU 10 stops the pressurizing pump 4. Then, the MPU 10 captures the cuff pressure _Pc (ST6), and further captures a pulse wave signal (ST7). The MPU ₁₀ applies the threshold value TH ₀ as shown in FIG. 3 to separate the pulse wave P _w (t) (ST8),
It is determined whether or not the break points T _st and T _en have been detected (ST
9). When the determination is NO, the process branches to ST7, and when the determination is YES, the process branches to ST10. That is, the processing of ST6 to ST9 is repeated until one pulse wave is obtained. The timing of capturing the cuff pressure _Pc may be during the detection of the pulse wave or after the detection of the pulse wave break point, or may be configured to sample together with the pulse wave signal and take an average value thereof.

In ST10, the MPU 10 uses the pulse wave parameters AMP, RAV, WID, CO
N is calculated, and a blood pressure value is determined using these parameters (ST11). Details of the processing of ST10 and ST11 will be described later.

In ST12, the MPU 10 opens the exhaust valve 3 to reduce the cuff pressure to zero, and causes the blood pressure value determined in ST11 to be displayed on the display 9 (ST11).
13) End the measurement. In the above description, one pulse wave is taken and the pulse wave parameter is calculated for this one beat. However, several pulse waves are taken, the pulse wave parameters are calculated for each of these several beats, and these are calculated. On average, reliability is improved.

Next, regarding the pulse wave parameter calculation process (ST10),
This will be described with reference to FIGS. 4 and 7.

In this example electronic blood pressure monitor, as a pulse wave parameter,
Pulse wave amplitude AMP, integration level RAV, waveform width ratio WID, flexion rate CON
Are adopted. Of course, the pulse wave parameters are not limited to these four.

First, the MPU 10 determines the time T at which the pulse wave Pw (t) becomes maximum and minimum.
_max, searching T _min, T _max, T _min to the corresponding pulse wave maximum value Pw _max, stores the pulse wave minimum value Pw _min in the memory 10a [ST 101, in FIG. 4 (a) refer to Fig. And from Pw _max
The pulse wave amplitude AMP is gathered by subtracting Pw _min (ST102).

Next, an integration level RAV [%], which is a value obtained by normalizing the time average of the pulse wave Pw (t) with the amplitude AMP, is calculated from the following equation (1) [ST103; see FIG. 4 (b)]. .

Subsequently, the waveform width ratio WID [%] is calculated.
04-ST108, see FIG. 4 (c)], and this WID is the pulse wave Pw.
The maximum value Pw _max predetermined time to decrease to the threshold TH ₁ than the appearance of (t), a normalized value in a cycle of the pulse wave (T _en -T _st).

First, to set the threshold TH ₁ by the following equation (2),
X in the equation (2) is a constant that is predetermined in the range of 0 to 1 (ST104).

TH ₁ = Pw _max + AMP × x (2) Next, the time t is set to T _max (ST105), and the sampling width Δt is added to this t (ST106), and the pulse wave P corresponding to the t is added.
w (t) is determined whether or not it is TH ₁ below (ST10
7). When the determination in ST107 is NO, the process branches to ST106, and when the determination is YES, the process branches to ST108. In ST108, WID is calculated from the following equation (3).

Here, T _dec is the time a Pw (t) ≦ TH _1.

Finally, the refractive index CON [%] is calculated (ST109 to ST11).
1). This CON is a reference connecting the maximum point and the minimum point of the pulse wave at a point T _cen which internally _divides the time section [T _max , T _min ] between the maximum point and the minimum point in one beat at a predetermined ratio y. Straight line L and pulse wave
This is a relative ratio to Pw (t).

First, T _cen is obtained by the following equation (4) (ST10
9). Here, y is a constant preset in the range of 0 to 1.

T _cen = T _max + (T _en −T _max ) × y (4) Next, the level Ref of the reference straight line L at T _cen is calculated by the following equation (5) (ST110).

Ref = Pw _max −AMP × y (5) Then, CON is calculated by the following equation (6).

Next, the blood pressure determination processing will be described with reference to FIG. 1, FIG. 8, and FIG. In the following description, the systolic pressure will be described, but the diastolic pressure can be similarly determined.

First, in ST201, the parameters AMP, RA obtained in ST10
Classification (ranking) for each of V, WID, and CON
Processing is performed. Since the data table of the membership function described later is discrete, a classifying process is required to correspond to this. Specifically, the process is performed by the following equations (7) to (10).

R _amp = AMP / I _amp … (7) R _rav = (RAV−O _rav ) / I _rav … (8) R _wid = (WID−O _wid ) / I _wid … (9) R _con = CON / I _con (10) where I _amp , I _rav , I _wid , and I _con are rank widths, respectively. Also, O _rav, O _wid is offset value. RAV
Since the minimum values of WID and WID are not zero, the offset values O _rav and O _wid are subtracted from these values, and then divided by the rank widths I _rav and I _wid .

In ST205 and thereafter, the blood pressure value is determined using the parameters R _amp , R _rav , R _wid , and R _con ranked in this manner. Before describing the specific processing, a data table will be described.

FIGS. 9 (a), (b), (c), and (d) are plots of measured data of AMP, RAV, WID, and CON obtained from a large number of subjects, plotted with the relative cuff pressure P _c ′ plotted on the horizontal axis. It is. What is shown in each figure is a so-called probability density distribution with parameters and relative cuff pressures as variables, and these are adopted as membership functions. In FIG. 9, if each pulse wave parameter is AMP ^* , RAV ^* , WID ^* , CON ^* , and if the respective membership functions are cut off at AMP ^* , RAV ^* , WID ^* , CON ^* , The cut edges are as shown in FIGS. 1 (a), (b), (c) and (d), respectively. 1 (a) (b) (c) (d)
It can be seen as a membership function selected for AMP ^* , RAV ^* , WID ^* , CON ^* .

In this embodiment, the parameters and the relative cuff pressure P _c '(for example, fixed in the range of -60 to +40 mmHg) are classified into ranks, and the membership functions are discretized and stored in the memory 10a in the form of a data table. ing. For example, the membership function data table for AMP is P _c ′,
If the AMPs are classified into m and n, respectively, they can be represented by the following matrix.

If AMP is calculated and its ranked value is R
_{In the case of amp} , a vertical column corresponding to R _amp is selected from the above matrix as a membership function corresponding to the value of AMP.

Returning to the description of the processing of ST202, in ST202, the initial value of the pointer j of the relative cuff pressure _Pc 'and the variable _Pmax storing the maximum value of the multiplied membership function are set to 0. ST
In 203, the above j is incremented by one, and in ST204, the membership function is multiplied by the following equation (11).

P (j) = P _amp (j, R _amp ) × P _rav (j, R _rav ) × P _wid (j, R _wid ) × P _con (j, R _con ) (11) In ST205, P (j ) _Is further multiplied by an estimated range limited membership function P _abs (j) to obtain P ′ (j).

P ′ (j) = P (j) × P _abs (j) (12) As shown in FIG. 2, the estimated range membership function sets the range of the absolute cuff pressure within the physiological range and the range of the systolic pressure as In this case, it is intended to limit the range to 50 to 260 mmHg. It is very rare that the systolic pressure is outside the range of 50 to 260 mmHg, and it occurs only in a very serious and special case, and is not measured by a general electronic sphygmomanometer.

Even if the pulse wave waveform is disturbed in P (j), even if the local maximum value occurs at a value far away from the relative cuff pressure corresponding to the actual systolic pressure, at such a value, P _abs (j ) Is zero, and as a result of multiplication, such a maximum value is excluded from P ′ (j), thereby preventing the relative cuff pressure from being erroneously estimated outside the physiological range [FIG. (E) (f)
(G)).

This estimated range limited membership function P _abs is also classified into m ′ and stored in the memory 10a in the form of a matrix.

[P _abs (1),..., P _abs (k),..., P _abs (m ')] Here, k is a pointer of the absolute cuff pressure as shown in FIG. Is converted into the pointer c of the relative cuff pressure by using the following equation. Here, R _pc is the discretization interval or P _cmin is the minimum value of the defined range of the relative cuff pressure.
If it is defined as ~ + 40mmHg, it will be -60mmHg.

j = k + P _cmin / R _pc (13) FIG. 1 (f) shows the estimated range limited membership function P _abs (j) converted in this way.

In ST206, it is determined whether or not P ′ (j) calculated in ST207 is larger than _Pmax . When the determination is YES, the process branches to ST207, and when the determination is NO, the process branches to ST208. ST
At 207, j and P '(j) are put into _Mmax and _Pmax , respectively. In ST208, it is determined whether or not j is equal to or greater than m. If this determination is NO, the process branches to ST203, and if YES, ST20
Branch to 9.

The processing of ST203 to ST208 is repeated until the determination of ST208 becomes YES, and this is repeated for each parameter AM as shown in FIG.
This can be said to be a process of calculating a function P 'obtained by multiplying the membership function and the estimation range limitation membership function for P, RAV, WID, and CON, and extracting the maximum value _Pmax .

In ST209, the following (1) was obtained from the obtained M _max and P _max.
The relative cuff pressure P _c ′ _* is estimated according to equation (4).

P _c ′ _* = P _cmin + (M _max −1) × R _pc (14) where P _cmin and _Rpc are the minimum value of the definition range of the relative cuff pressure and the discretization interval, respectively, as described above. .

In ST210, the systolic pressure P _SYS is calculated by adding the current cuff pressure P _c (ST6) to the estimated relative cuff pressure P _c ′ _* .

P _SYS = P _c ′ _* + P _c (15) In this embodiment, the estimation range limited membership function P _abs is a trapezoidal function as shown in FIG. 2, but is not limited to this. Instead, the design can be changed as appropriate.

Further, in this embodiment, multiplication is applied to the logical calculation. However, other logical calculations such as addition may be applied, and the design can be changed as appropriate.

(G) Effect of the Invention As described above, in the electronic sphygmomanometer of the present invention, the membership function storage means stores the estimation range limiting membership function for limiting the estimation range of the relative pressure, and the blood pressure value determination means In addition to the selected membership function, the relative pressure is estimated using the estimated range limited membership function. Therefore, even if the pulse wave waveform is disturbed by pressure noise or the like and some parameters are affected, the obtained blood pressure value is prevented from being outside the physiological range, and there is an advantage that accurate blood pressure measurement can be performed. doing.

[Brief description of the drawings]

FIG. 1 is a diagram showing a membership function for explaining a blood pressure value determination process of the electronic sphygmomanometer according to one embodiment of the present invention, and FIG. 2 is a diagram showing an estimation range limited membership function of the electronic sphygmomanometer. FIG. 3, FIG. 3 is a waveform diagram for explaining the division of the pulse wave of the electronic sphygmomanometer, FIG. 4 is a waveform diagram for explaining the pulse wave parameter calculation process of the electronic sphygmomanometer, and FIG. FIG. 6 is a block diagram illustrating the configuration of the electronic sphygmomanometer, FIG. 6 is a flowchart illustrating the overall operation of the electronic sphygmomanometer, and FIG.
FIG. 8 is a flowchart illustrating a parameter calculation process of the electronic sphygmomanometer, FIG. 8 is a flowchart illustrating a blood pressure value determination process of the electronic sphygmomanometer, FIG. 9 (a), FIG. 9 (b) , FIG. 9 (c) and FIG. 9 (d) are diagrams showing actually measured data for explaining the relationship between the pulse wave amplitude, the integration level, the waveform width ratio, and the bending ratio with the relative cuff pressure. 2: Cuff, 3: Exhaust valve, 4: Pressure pump, 5: Pressure sensor, 7: Band pass filter, 10: MPU, 10a: Memory, P _c : Cuff pressure, P _c ′: Relative cuff pressure, AMP: pulse wave amplitude, RAV: integration level, WID: pulse wave width ratio, CON: _{tortuosity, P amp · P rav · P} wid · P con: membership functions, P _abs: estimation range limited membership functions.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) A61B 5/022

Claims (1)

(57) [Claims] 1. A cuff worn on a subject, a pressurizing means for pressurizing air in the cuff to a predetermined pressure, an exhausting means for exhausting air in the cuff, and a pressure for detecting an air pressure in the cuff. Detecting means, a pulse wave detecting means for detecting the subject's pulse wave, and a pulse wave parameter calculating means for calculating a plurality of parameters representing the pulse wave waveform from the pulse wave detected by the pulse wave detecting means, For each of these parameters, a membership function storage unit that stores a membership function that changes each parameter and a relative pressure of the air pressure in the cuff with respect to the blood pressure value is calculated by the pulse wave parameter calculation unit. A member function for selecting a membership function corresponding to each parameter from the membership functions stored in the membership function storage means. A membership function selecting means, and a blood pressure value determining means for performing a predetermined logical calculation on the membership function for each parameter selected by the membership function selecting means, estimating the relative pressure and determining a blood pressure value. In the electronic sphygmomanometer, the membership function storage unit stores an estimation range limiting membership function that limits the estimation range of the relative pressure, and the blood pressure value determination unit includes, in addition to the selected membership function, An electronic sphygmomanometer for estimating the relative pressure using the estimated range limited membership function.