JPH0636785B2 - Electronic blood pressure monitor - Google Patents

Description

TECHNICAL FIELD The present invention relates to improvement of pulse wave component detecting means of an electronic sphygmomanometer that employs a vibration method.

(B) Conventional technology Conventionally, as an electronic sphygmomanometer that handles pulse wave signals, a cuff, a pressurizing pump that pressurizes the air in the cuff (hereinafter referred to as pressurizing the cuff), and depressurizes the air in the cuff. An exhaust valve,
A pressure sensor that detects the pressure of the air in the cuff (hereinafter referred to as the cuff pressure), a high-pass filter that detects the pulse wave component of the output signal of this pressure sensor, and a blood pressure value based on the output signals of the pressure sensor and high-pass filter. There is known one provided with a microcomputer (MPU) as a quantitative means for quantitatively determining.

The operation of this one will be described with reference to FIGS. 6 and 7.

FIG. 6 shows the relationship between the cuff pressure and the elapsed time during the measurement operation. A state in which the cuff is wrapped around the upper arm of the human body and the cuff is pressurized to a predetermined pressure is shown as point A. Pressurization is stopped here, and the exhaust valve starts exhausting at a constant fine speed. During this evacuation process, the arteries whose blood flow was stopped by the cuff,
The pulse pressure from the heart trying to flow blood is transmitted to the cuff, and the pulse wave W as shown in FIG. 6 is generated. This pulse wave W
Becomes gradually larger as the cuff pressure decreases, reaches its maximum amplitude, and then gradually attenuates. The reason why the pulse wave is attenuated is that when the cuff pressure is lowered to some extent, the blood smoothly flows into the artery and the pulsation from the heart is not transmitted to the cuff.

FIG. 7 shows the relationship between the amplitude of the pulse wave component and the elapsed time during the measurement operation. At the beginning, the pulse wave component width value gradually increases, but increases sharply from point S in the figure. Then, after reaching the maximum value at the point M, it rapidly decreases and then gradually decreases from the point D. At this time, it is empirically known that the cuff pressure corresponding to the point S becomes the maximum blood pressure value and the cuff pressure corresponding to the point D becomes the minimum blood pressure value. The microcomputer obtains the points S and D from the pulse wave component data and determines the systolic blood pressure value and the diastolic blood pressure value.

When the pulse wave W disappears, the data necessary for calculating the blood pressure value can no longer be obtained, so the exhaust valve is opened, the cuff pressure is rapidly dropped (point B in FIG. 6), and the measurement is completed. To do.

(C) Problems to be solved by the invention However, in this device, the cutoff frequency of the high-pass filter was fixed at about 0.5 Hz, but due to its transient response, as shown in FIG. A pulse wave may be generated before the baseline level of the output signal of the high pass filter is stabilized. In this case, since accurate pulse wave component data cannot be obtained, there is a possibility that accurate blood pressure measurement cannot be performed.

Therefore, in order to take time (usually 2 to 3 seconds) for the baseline level of the output signal of the high-pass filter to rise, the cuff pressure is first increased to a value higher than usual, and the pulse wave is generated from the start of the slow speed exhaustion. It is necessary to take a long time or hold the state for several seconds when the cuff pressure is first applied, but this is not necessary for the person to be measured because the cuff pressure is high or the measurement time becomes long. I was in pain.

Also, in order to speed up the stabilization of the output signal of the high-pass filter to the baseline level, the cut-off frequency of the high-pass filter is increased, for example, 5 Hz. Since the frequency of the pulse wave is usually less than 5 Hz, the pulse wave component However, there was an inconvenience that accurate measurement could not be performed.

The present invention has been made in view of the above inconvenience, and an object thereof is to provide an electronic sphygmomanometer capable of accurately measuring a blood pressure value without giving unnecessary pain to a subject.

(D) Means for Solving the Problems Means for solving the above inconveniences will be described below with reference to FIG. 1 showing the basic concept of the present invention.

The cuff 1 has a pressurizing unit 2, a depressurizing unit 3, and a pressure detecting unit 4.
, But connected via a conduit. One of the outputs of the pressure detection means 4 is input to the quantification means 6, and the other output is detected by the pulse wave component detection means 5 as a pulse wave component and input to the quantification means 6.

The pulse wave component detecting means 5 is additionally provided with a cutoff frequency varying means 7 for varying the cutoff frequency.

(E) Operation The operation of the present invention will be described with reference to FIG.

First, at the time when the cuff is pressurized and the slow speed exhaust is started, the cutoff frequency varying means 7 causes the pulse wave component detecting means 5 to operate.
Set the cutoff frequency of to higher than usual. Therefore, the baseline level of the pulse wave component rapidly decreases as shown in FIG. On the other hand, the cutoff frequency varying means 7
As the time passes or the cuff pressure value decreases, the cutoff frequency of the pulse wave component detecting means 5 is lowered to a normal value in a stepwise or continuous manner. To be detected.

(F) Embodiment An embodiment of the present invention will be described below with reference to FIGS. 2 to 5.

FIG. 2 shows an external perspective view of the electronic sphygmomanometer of the present invention,
Reference numeral 1 denotes a cuff that is in the shape of an air pillow when expanded, and is connected to the sphygmomanometer body 25 by a flexible tube 23 made of rubber or the like. On the upper surface of the sphygmomanometer main body 25, a display device 20 including a liquid crystal display device, a power switch 21, and a measurement switch 22 are provided.

FIG. 3 shows a block diagram of an air system and a measuring circuit of the electronic blood pressure monitor of this embodiment. Cuff 1, tube 23 and piping 2
It is connected to the pressurizing pump 12, the exhaust valve 13 and the pressure sensor 14 via 4a, 24b and 24c. Pressure sense 1
As for 4, a diaphragm type pressure converter using a strain gauge, a semiconductor pressure converting element, or the like can be appropriately used. The pressurizing pump 12 and the exhaust valve 13 are controlled by a microcomputer (MPU) 16 described later.

On the other hand, the output of the pressure sensor 14 is the amplifier 18 and the A / D.
It is input to the microcomputer 16 via the converter 19. The microcomputer 16 includes a pulse wave component detecting means 5, a quantifying means 6 for quantifying a blood pressure value, and a controlling means for controlling the pressurizing pump 12 and the exhaust valve 13.

The microcomputer 16 includes a display device 20 for displaying the blood pressure value obtained by the quantification means 6 and a power switch 21.
And the measurement switch 22 is connected.

Next, the operation of the electronic sphygmomanometer according to this embodiment will be described below with reference to FIGS. 4 and 5.

First, the cuff 1 is wrapped around the upper arm of the person to be measured, the power switch 21 is turned on, and then the measurement switch 22 is turned on.

Continuing the description with reference to the flowchart of FIG. 4, the microcomputer 16 operates the pressurizing pump 12 to start pressurizing the cuff 1 (step ST1). In the next step ST2, it is determined whether or not the cuff pressure has reached a predetermined value, and if the cuff pressure has not reached the predetermined value, this determination process is repeated. When the cuff pressure reaches a predetermined value, the pressurizing pump 12 is stopped (step ST3), and the exhaust valve 13 starts exhausting at a constant fine speed (step ST4). Next, the flag value F is set to 0 and the control variable j is set to 1 (step S
T5), starts to count the timer _{T 3} for switching the cutoff frequency fc of the pulse wave detecting means 5 (step ST6).

In the next step ST7, the control variable i and Pt described later are
Are both zero. In step ST8, the timer _{T 2} for measuring the time interval for detecting the pulse wave component, step ST9
Then, the count of the timer T ₁ for measuring the cycle of sampling the cuff pressure value Pc (i) is sequentially started. In step ST10, it is determined whether or not the timer T ₁ has timed out, and if it has timed out, the next step ST
Proceed to 11.

In step ST11, the control variable i is incremented by 1 and the cuff pressure value Pc (i) is sampled (step ST1).
2). In the next step ST13, this cuff pressure value Pc
(i) is added to the cumulative value Pt for obtaining the sum of the cuff pressure values and calculating the average value. Further, in step ST14, the value Pu (i) of the pulse wave component is detected, the details of which will be described later.

Next, it is determined whether or not the timer T ₂ has timed out (step ST15). When the timer T ₂ is determined to not timed in step ST15, step ST
Returning to step 9, the processes of steps ST9 to ST14 are repeated.
On the other hand, if the timer T ₂ in step ST15 is determined to be time-up, that is, if one pulse wave period has elapsed, the flow proceeds to the next step ST16.

In step ST16, the pulse wave amplitude value Ap (j) is calculated. As the calculation means, in this embodiment, step ST1
The pulse wave amplitude value Ap (j) is the value obtained by subtracting the minimum value from the maximum value in the Pu (i) sequence obtained in 4. In the next step ST17, Pt is divided by i to obtain Pc (i)
Of the cuff pressure value P (j) corresponding to the pulse wave amplitude value Ap (j). The means for obtaining the cuff pressure value P (j) is not limited to this, and can be appropriately changed, for example, the latest one of the cuff pressure values Pc (i) is set to P (j). In the subsequent step ST17, the control variable j is incremented by 1.

In the next step ST19, when it is determined that the pulse wave amplitude value Ap (j) is not increasing, the process proceeds to step ST21,
If it is determined that the number is increasing, step ST20
Then, the flag value F is set to 1, and the process returns to step ST7. Hereinafter, while the pulse wave amplitude value Ap (j) continues to increase, step S
Repeat T7 to ST18 to obtain new cuff pressure value Pc (i) sequence and pulse wave component value Pu obtained in steps ST9 to ST14.
The pulse wave amplitude value Ap (j) is continuously searched from the column (i).

When the pulse wave amplitude Ap (j) ceases to increase (when it exceeds the point M shown in FIG. 7), the flag value F =
It is determined whether or not 1, and if F = 1, it means that the increasing pulse wave amplitude value has turned downward, and thus step ST22 follows.
If F ≠ 1, the process proceeds to step ST25.

In step ST22, among the pulse wave amplitude value Ap (j) columns,
Extract the maximum value ApMAX. In the next step ST23, the pulse wave amplitude value A that is about 50% of the maximum value ApMAX.
p () (1 << j) is searched, and the cuff pressure value P () corresponding to the searched pulse wave amplitude value Ap () is set as the systolic blood pressure value P _SYS , and the memory of the microcomputer 16 (not shown). ) To remember. Furthermore, step ST24
Then, the flag value F is set to zero, the process returns to step ST7, and steps ST7 to ST19 are performed again.

When the process proceeds to step ST21 again, since the flag value F is zero, that is, the pulse wave amplitude value has already turned down, the process proceeds to step ST25, and thereafter, the pulse wave amplitude value Ap (j) is Of the pulse wave amplitude values Ap (j) that are about 70% of the maximum value ApMAX, the latest value Ap (m) (1 <
m ≦ j), and the cuff pressure value P corresponding to this Ap (m)
(m) is stored in the memory of the microcomputer 16 as the minimum blood pressure value P _DIA (step ST25).

In the next step ST27, the systolic blood pressure value P _SYS and the diastolic blood pressure value P _DIA stored in the memory are read out and displayed on the display 9. Further, in step ST28, the microcomputer 16 causes the exhaust valve 13 to perform rapid exhaust, and ends one measurement operation.

The means used for obtaining the systolic blood pressure value P _SYS and the diastolic blood pressure value P _DIA in steps ST23 and ST26, respectively, are simple, but as in the prior art, from the pulse wave amplitude Ap (j) sequence, The S point at which the pulse wave amplitude value suddenly increases and the D point at which the pulse wave amplitude suddenly decreases shown in FIG. 7 are obtained, and the systolic blood pressure value P _{SYS is calculated} from the corresponding cuff pressure value P (j) column. And the minimum blood pressure value P _DIA can also be determined.

Next, the pulse wave component Pu (i) detection processing in step ST14 will be described in more detail with reference to FIG.

First, the principle of the method for obtaining the pulse wave component value Pu (i) from the cuff value Pc (i) sequence will be described. n is an integer, x (n), y (n) and z (n) variables, and α and β are parameters. At the beginning,
Let x (n) be the cuff pressure value Pc (i) [Equation (1)].

x (n) = Pc (i) (1) Here, z (n-1), y (n-1), and x (n-1) are calculated when Pu (i-1) is calculated. , That is, z (n), y (n), x (n)
Means the value immediately before.

αy (n) -βy (n-1) = x (n) -x (n-1) (2) y (n) obtained by the formula (2) is converted to z of the formula (3) described later. Put it as (n).
The expression (3) is an expression of the same form as the expression (2), and finally y (n) is determined here.

αy (n) -βy (n-1) = z (n) -z (n-1) (3) y (n) obtained from the equation (3) is the value of the pulse wave component Pu ( i).

Pu (i) = y (n) (4) The filter cutoff frequency fc of the pulse wave component Pu (i) detecting means is determined by the values of the parameters α and β.
The values of the parameters α and β with respect to the cutoff frequency fc used in this embodiment are as follows.

From the above description, regarding the variable sequences x (n), y (n), z (n), the previous x (n-1), y (n-1), z (n-1) Since it is used only, only the previous value can be stored in the memory in the actual arithmetic processing, and the capacity of the memory can be saved.

As a specific process, as shown in FIG. 5, the timer T ₃ is checked in step SP1. When the count time of the timer T ₃ is less than t ₁ , the process proceeds to step SP2, when it is less than t ₂ , the process proceeds to step SP3, and when it is t ₂ or more, the process proceeds to step SP4.

In step SP2, α = 1.0055 and β = 0.9945 are set, and the cutoff frequency fc is 5 Hz in the following arithmetic processing.
Is done. Similarly, in steps SP3 and SP4, α and β are set as described above, and the cutoff frequencies fc are set to 1 Hz and 0.5 Hz, respectively.

The above t ₁ and t ₂ are respectively 0.1 in this embodiment.
Seconds are set to 0.2 seconds. Step S shown in FIG.
In T6, the cutoff frequency fc from the time the timer T ₃ is started until after 0.1 seconds 5 Hz, the cutoff frequency fc to the elapsed 0.2 seconds 1 Hz, the cutoff frequency fc of after 0.2 seconds is 0.5Hz . Cutoff frequency f
c = 0.5 Hz is a normal value for extracting the value Pu (i) of the pulse wave component, and fc = 1 Hz and fc = 5 Hz are for quickly stabilizing the baseline level of the pulse wave component. is there.

In any of steps SP2 to SP4, the parameter α,
When the value of β is set, the process proceeds to the next step SP5, and it is determined whether or not the control variable j of the main routine (FIG. 4) is 1, and when j = 1, Xb and Y are determined at step SP6.
When b is zero, the process proceeds to step SP7, and when j ≠ 1, the process directly proceeds to step SP7. Xb and Yb are x (n in the above description.
-1), y (n-1), respectively, and is set to zero as an initial value.

In the next step SP7, the cuff pressure value Pc (i) is put into Xa [corresponding to x (n)], and in step SP8, based on the equation (2), Xa, Xb, and Yb are used to calculate Ya [y (n ))
To calculate. Further, in the next step SP9, Ya is set in Za and Yb is set in Zb [Za and Zb are z
(n), corresponding to z (n-1)], based on these equations Yb, Za and Zb, Ya is calculated again in step SP10 based on the equation (5). This Ya is set as the pulse wave component value Pu (i) (step SP11), finally Xa is put into Xb and Ya into Yb (step SP12), and the process returns to the main routine.

In the pulse wave component Pu (i) detecting means of this embodiment, the cutoff frequency fc is reduced in three steps, but it can be reduced in two steps, four steps or more, or continuously. The value of the cutoff frequency in each stage and the duration of each stage can be changed appropriately.

Further, in this embodiment, although reduced by switching the cutoff frequency fc by the timer T _3, the cut-off frequency fc, for example, by whether the cuff pressure is initially reduced percentage than when the cuff is pressurized Alternatively, the cutoff frequency may be manually changed by providing a cutoff frequency changeover switch in the sphygmomanometer main body 25.

Further, the pulse wave component Pc (i) detecting means of this embodiment is included in one microcomputer 16 together with the quantifying means 6 etc., but a microcomputer for the pulse wave component Pu (i) detecting means etc. Can be separately provided, and the design can be appropriately changed.

In addition, in this embodiment, the pressurizing pump 12 and the exhaust valve 13 are configured to be automatically operated by the microcomputer 16, but the pressurizing pump 12 and the exhaust valve 13 may be manually operated. it can.

(G) Effect of the Invention Since the present invention is provided with the cutoff frequency varying means for switching the cutoff frequency of the pulse wave component detecting means, and the determining means for determining the switching time point of the cutoff frequency, the pulse wave Since the baseline level of the output signal of the component detecting means is rapidly stabilized, it is not necessary to pressurize the cuff additionally, the measuring time is shortened, and the pain felt by the person to be measured can be suppressed to the necessary minimum.

Further, in order to rapidly stabilize the baseline level of the output signal of the pulse wave component detection means, the cutoff frequency is set high, and as a result, there is no inconvenience that the pulse wave component cannot be accurately detected, and accurate blood pressure measurement is possible. There is an advantage that can be done.

[Brief description of drawings]

FIG. 1 is an explanatory view for explaining the basic concept of the present invention, and FIG.
FIG. 1 is an external perspective view of an electronic sphygmomanometer according to an embodiment of the present invention, FIG. 3 is a circuit block diagram showing an outline of a circuit of the electronic sphygmomanometer, and FIG. 4 shows an operation of the electronic sphygmomanometer. 5 is a flow chart for explaining the details of the pulse wave component detection processing in the electronic blood pressure monitor, and FIG. 6 is an explanatory diagram for explaining the relationship between the elapsed time during the measurement operation and the cuff pressure. , FIG. 7 is an explanatory view for explaining the relationship between the elapsed time and the pulse wave amplitude value,
FIG. 8 is an explanatory view for explaining the relationship between the elapsed time and the pulse wave component in the conventional electronic blood pressure monitor, and FIG. 9 is an explanatory view for explaining the relationship between the elapsed time and the pulse wave component in the electronic blood pressure monitor according to the present invention. It is a figure. 1: cuff, 2: pressurizing means, 3: depressurizing means, 4: pressure detecting means 5: pulse wave component detecting means, 6: quantitative measuring means, 12: pressurizing pump, 13: exhaust valve, 16: microcomputer.

Claims (3)

[Claims] 1. A cuff, a pressurizing means for pressurizing a fluid in the cuff, a depressurizing means for depressurizing the fluid in the cuff at a constant slow speed or rapidly, and a pressure detecting means for detecting the fluid pressure in the cuff. , A pulse wave component detecting means for cutting a component having a frequency equal to or lower than a predetermined frequency of the output signal from the pressure detecting means, and detecting a pulse wave component included in the output signal, and the pressure detecting means and the pulse wave component detecting means. An electronic sphygmomanometer including a quantifying means for quantifying a blood pressure value based on an output signal, a cutoff frequency varying means for switching a cutoff frequency of the pulse wave component detecting means, and a discriminating means for discriminating a switching time point of the cutoff frequency. The cutoff frequency varying means sets the cutoff frequency higher than the cutoff frequency at the time of detecting the pulse wave component immediately after the pressure reduction is started, and the cutoff frequency varying means sets the cutoff frequency based on the output of the determining means. An electronic sphygmomanometer characterized by switching the toff frequency. 2. The electronic sphygmomanometer according to claim 1, wherein the cutoff frequency varying means includes a clocking means, and the cutoff frequency is changed based on the time counted by the clocking means. 3. The electronic sphygmomanometer according to claim 1, wherein the cutoff frequency varying means changes the cutoff frequency based on an output signal from the pressure detecting means.