JPH02111339A - Electronic tonometer - Google Patents

Abstract

PURPOSE:To enable sphygmomanometry to be performed of high repeatability by extracting a pulse wave component in a pressure reducing process of an arm band, calculating pulse wave mean ratio of each pulse wave from its maximum, minimum and mean value and a blood pressure value to be determined from start and end points of a linear increase section of the pulse wave mean ratio. CONSTITUTION:A cuff (arm band) 1 is connected through a pipe 2 to an exhaust valve 3 having fine and rapid speed exhausting functions, pressure pump 4 and a pressure sensor 5. The pressure pump 4 is constituted so as to be on/off turned by a command from a CPU 9, and the exhaust valve 3 is similarly constituted such that its quick exhaust function is turned on by a command signal (a). The pressure sensor 5 converts a pressure in the cuff 1, received through the pipe 2, into an electric signal amplified by an amplifier 6, converted into a digital signal by an A/D converter 7 and fetched to the CPU 9. A cuff internal pressure signal, output from the amplifier 6, is taken out by a band pass filter 8 only in the pulse wave component converted into a digital signal by the A/D converter 7 and fetched to the CPU 9. The CPU 9, executing a process for calculating a blood pressure, displays its measured value in a display device 10.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a non-invasive electronic blood pressure monitor using a wristband, and particularly to an electronic blood pressure monitor employing the oscillometric link method.

(b) Conventional technology In general, when a cuff is wrapped around an arbitrary measurement site and the pressure is gradually reduced after applying pressure with a pressure pump, etc., the pressure inside the cuff increases in synchronization with the pulse. Vibration occurs. This pressure vibration is called a pulse wave, and the oscillometric method is a general term for a method of calculating (determining) blood pressure by analyzing the waveform of this pulse wave. The conventional oscillometric method calculates blood pressure by recognizing changes in the amplitude of the pulse wave described above. In other words, when the arm cuff pressure is increased above the systolic pressure (systolic pressure) and then gradually reduced, the amplitude of the pulse wave is small at first, then gradually increases until the arm cuff pressure becomes equal to the mean blood pressure. After reaching the maximum amplitude,
Conventionally, by taking advantage of the property that the pulse wave amplitude gradually decreases, the pulse wave amplitude is calculated based on the point at which the pulse wave amplitude becomes equal to the relative level (X%, Y%) calculated based on the maximum amplitude. How to determine arm cuff pressure as systolic pressure or diastolic pressure (diastolic pressure) (see Figure 9), and how to determine the arm cuff pressure at the point when the rate of increase or decrease in pulse wave amplitude suddenly increases or decreases. Blood pressure was calculated by determining the systolic pressure and diastolic pressure, respectively (see Fig. 10).

(c) Problems to be Solved by the Invention The behavior of pulse wave amplitude inherently differs greatly from individual to individual. Therefore, in the former conventional method described above, the pulse wave amplitude at the true systolic pressure or diastolic pressure is not necessarily a constant ratio to the maximum pulse wave amplitude. Furthermore, in the latter conventional method, the point of change in the rate of increase or decrease in pulse wave amplitude is often unclear. For the above reasons, no matter which of the conventional oscillometric methods is adopted, there is a problem in that a large ml+constant error often occurs.

This invention has been made by focusing on the above-mentioned problems, and uses a parameter with small individual differences and a clear change in i'jaM, that is, a pulse wave parameter other than pulse wave amplitude.
The objective is to provide a highly accurate and reliable electronic blood pressure monitor that uses the oscillometric method.

(d) Means and Effects for Solving the Problems The electronic blood pressure monitor of the present invention includes an arm cuff, a pressurizing means for pressurizing the arm cuff, a pressure detecting means for detecting the pressure of the arm cuff, and a pressure detecting means for detecting the pressure of the arm cuff. an exhaust means for reducing the pressure of the pressure, a pulse wave extracting means for extracting a pulse wave component from the pressure signal of the pressure detecting means, and a maximum value and minimum value of the pulse wave for each beat of the extracted pulse wave. and means for calculating the average value, and the formula R=(average value of pulse wave−minimum value of pulse wave)/(maximum value of pulse wave−minimum value of pulse wave)×100 [
%]; linear change section detecting means for recognizing a linearly changing section of the pulse wave average ratio R during the slow change process of the pressure of the arm cuff; and blood pressure determination means for determining the blood pressure value from the cuff pressure corresponding to the start point and/or the end point of the change section.

Here, FIG. 1, which describes the properties of the pulse wave average ratio R, shows changes in the pulse wave average ratio R during the process of decreasing the internal cuff pressure. This is based on clinical data obtained from 260 subjects, and the systolic pressure (SYS) and diastolic pressure (
It is plotted on the arm cuff internal pressure axis normalized by DIA). The numerical value on the horizontal axis indicates the pressure difference when 5YS-DIA is taken as 100%. This figure shows that during the cuff decompression process, the pulse wave flat and restraint R tend to decrease slightly in the cuff internal pressure region that is higher than the systolic pressure, but suddenly start to decrease from around the systolic pressure point (point 873 in the figure). It begins to increase and increases almost monotonically and linearly until the diastolic pressure point (DIA point). Then, it reaches about 50% at the diastolic pressure point, and thereafter tends to decrease again. The properties of such pulse wave average ratio R are shown in Figure 2 (a
) (b) As shown in (C), the change is caused by the change in the pulse waveform during the cuff decompression process, but it is a stable change without individual differences, and there is a noticeable change in the feature amount corresponding to blood pressure. Observed. Thus, by using the pulse wave average ratio R, it is possible to measure blood pressure with high reproducibility.

That is, in this electronic blood pressure monitor, for example, the pulse wave component is extracted during the decompression process of the arm cuff, the maximum value, minimum value, and average value of each pulse wave are calculated, and the pulse wave component is calculated from these maximum, minimum, and average values. The wave average ratio is calculated, and during the decompression process, a linearly increasing section of this pulse wave average ratio is detected, and the systolic pressure and diastolic pressure are calculated and determined from the start and end points of the detected linearly increasing section. be done. Although the above description has been made of a blood pressure monitor that detects changes in the pulse wave average ratio during the depressurization process of the cuff and calculates the blood pressure value, this may also be performed during the slow pressurization process.

(E) Examples The present invention will be explained in more detail with reference to Examples below.

FIG. 3 is a block diagram showing the hardware configuration of an electronic blood pressure monitor in which the present invention is implemented.

In the figure, a cuff (arm cuff) 1 is connected via a vibrator 2 to an exhaust valve 3 having a slow exhaust function and a rapid exhaust function, a pressure pump 4, and a pressure sensor 5. The pressurizing pump 4 is turned on by a command from the CPU 9,
Further, the exhaust valve 3 is configured so that the rapid exhaust function is turned on by the same command signal a from the CPU 9.

The pressure sensor 5 converts the pressure inside the cafe received through the pipe 2 into an electrical signal, outputs this and amplifies it with the amplifier 6, converts it into a digital signal with the A/D converter 7, and sends it to the CPU 9.
be taken in. On the other hand, since the arm cuff internal pressure signal outputted from the amplifier 6 includes a pulse wave component, only the pulse wave component is derived by the band pass filter 8, and this is converted into a digital signal by the same A/D converter 7. Convert and import into CPU9.

The CPU 9 executes processing for calculating blood pressure, which will be described later, and displays the measured value on the display 2310.

However, the hardware configuration of the electronic blood pressure monitor shown here is not particularly different from the configuration of the conventional oscillometric link electronic blood pressure monitor. Therefore, the pressure sensor 5 is the semiconductor sensor J
It may also be a combination of a J. or bellows type sensor and an oscillator. Moreover, the band pass filter 8
It may also be a digital filter constructed in software within Q. The present invention is characterized by the blood pressure calculation algorithm executed by the CPU 9.

Next, the blood pressure measurement operation of the electronic blood pressure monitor will be explained with reference to the flowcharts shown in FIGS. 4, 5, and 6.

When a start switch (not shown) is turned on, the process shown in FIG. 4 starts, and first, in step ST (hereinafter abbreviated as STI) 1, each variable used for blood pressure calculation is initialized. Here, if we enumerate the functions of each variable, t is the pulse wave data PW (
t) counter, n is a pulse counter (also a counter for the calculated pulse wave average ratio R), DH, M, Dl, IAX
are the minimum and maximum values of the first and second order differences of the pulse wave average ratio R, F
SVS and F DIA are flags indicating that systolic pressure and diastolic pressure have been obtained.

Following initialization, the pulse wave data PW(t) is read through the A/D converter 7 (Sr1), and the pulse wave data PW(t)
The counter t is incremented by 1 (5T3), and the break point is detected in order to break the pulse wave after one beat (Sr1).
. Detection of this break point is realized by processing such as detecting the intersection of the pulse wave and the dark value provided in the pulse wave data, as shown in FIG. Next, it is determined whether or not a breakpoint is detected (5T5), and until a breakpoint is detected,
The processes from Sr1 to Sr1 are repeated, that is, the pulse wave data PW(t) is read. When the break point is detected, the determination in ST'5 becomes YES, and the pulse wave average ratio R(n) is calculated here.

The details of the calculation process of this pulse wave average ratio R(n) will be described later.

Once the pulse wave average ratio R(n) is determined, the variable n is then incremented by 1 (5T7), and the primary and secondary difference values of the pulse wave average ratio R are calculated (Sr1).

This calculation is based on the formula: first difference value = R1l Rfn-1 and second difference value Dz+n1=D++n+ DI+I! -11. Subsequently, the −th order difference value D10. , the minimum value D
HIN and the maximum value D□8 are updated (Sr1).

This updated value is Dl from the start of measurement.

are the minimum and maximum values of Next, blood pressure determination processing is performed using the minimum value [), +s, and maximum value DHAX of the negative difference values (STIO). Details of this blood pressure determination process will be described later. It is determined whether the blood pressure has been determined (STII), and if both the systolic pressure and the diastolic pressure have been determined, the process proceeds to 5T12 and subsequent steps, but if not, the process returns to Sr1 and is repeated. Whether or not the blood pressure has been determined is determined by whether the systolic pressure determination flag FSYI and the diastolic pressure determination flag FDIA are both 1. After blood pressure has been determined, moving to 5T12, the elephant of exhaust valve 3,
ONL quick exhaust, the pressure inside the cuff is released. and,
The blood pressure value is displayed on the display 10 (ST13), and the entire process ends. .

Next, details 4111 of the calculation process of the average pulse wave ratio R(n) in ST6 will be explained with reference to the flowchart shown in FIG.

First, in Sr61, each variable is initialized.

Here, t' is a time counter dedicated to the following average ratio calculation process, and TOEV is the value of the counter t at the break point one beat before. Therefore, by assigning the variable T DEVO value to the variable t', the series of processes for calculating the average ratio is started from the break point one beat before. P
WHAX is a variable that indicates the maximum value of pulse wave data, PWMIN
is a variable indicating the minimum value of pulse wave data. In ST62, the value of pulse wave data PW(L') is compared with the variable PWMAX, and if PW, , <PW(L'), PW(t
') as the new PWMAX and update PWHAX (
ST63). That is, the maximum value of PW(t') is stored in PW□8 every time.

Therefore, in the subsequent processing, PW,^,<PW(t”)
If not, ST63 is skipped. Next, ST
In ST64, the variable PW1.11N is compared with PW(t'), and if PW,N>PW(t"), PW(t") is set as a new PWHlN and pw, , are updated (ST6
5). Then, in ST66, PW(L') is sequentially added to the variable T OT A L.

Next, in ST67, the counter t' is compared with a variable indicating the current time, and if t' = t, that is, if the series of processing has been performed up to the current break point, the process advances to ST69. On the other hand, if it is not t'-t, the process returns to 5T62 and the process is repeated again. In 5T69, the variable TOTAL counters the counter value T, at the previous breakpoint. and P
The pulse wave average ratio R(n) is calculated using WMAX% R and 41N as shown in the following equation.

Then, in preparation for the next average ratio calculation process, the current breakpoint time is stored in the variable T_DEV, the process ends, and the process returns to the main flow.

Next, details of the 5TIO blood pressure determination process will be explained with reference to the flowchart shown in FIG.

First, check the systolic pressure determination flag FSYS at 5TIOI and see if Fsvs=1? In other words, it is determined whether the systolic pressure has been determined. If Fsys=O1, that is, the systolic pressure has not been determined, the process advances to 5T102 and the subsequent systolic pressure determination process begins.

In 5T102 to 5T106, it is determined whether the pulse wave average ratio R has entered the linear increasing section. In 5T102, -
It is determined whether the order difference value DI (Ill is positive or not. In other words, DI+, , ) > O, the pulse wave average value ratio R is on an increasing trend, and there is a possibility that it is in a linear increasing part. In this case, move to 5TIO3 and set counter C1 to 1.
Increment.

However, in 5TI02, if D+tn)≦0, it is assumed that there is no possibility and returns without performing any processing.

The counter C2 is for counting the number of beats after the pulse wave average ratio R starts to increase. At 5T104, it is determined whether the count value of the counter C2 is 4 or more, and if it is 4 or more, it is determined that the pulse wave average ratio R is definitely increasing, and the process moves to 5TI05. If the count value of the counter C1 is less than 4, it is determined that the increasing tendency of the pulse wave average ratio R cannot be determined, and the process returns without performing any processing.

5T105, the -order difference value D10. The minimum value of DMIN
The maximum value, the ratio of Ai, and the value of DMAi/D□9 are compared with constants, and it is determined whether D□X/D)11N is greater than or equal to 1. This comparison process is to determine whether the pulse wave average ratio R is increasing linearly, and as shown in FIG. 8(a), when the pulse wave average ratio R enters the linear increasing section, It takes advantage of the property that the rate of increase is clearly greater than the rate of decrease up to that point. That is, the maximum rate of decrease before it is determined that the pulse wave average ratio R has entered the increasing section at 5T104, 4. , and the rate of increase D since it started increasing.
If the ratio with HAX is not above a certain level (K, above), it is determined that the linear increasing section is dangerous and the process returns from ST105. This takes into account, for example, the influence of noise.

5T105, 1 is YES for DMAK/DMIN≧
In the case of determination, it is definitely a linear increasing section, and 5T
Moving on to 106. In this 5T106, it is determined whether condition 1 is satisfied. Condition 1 here means D2+-1+D2
I-2. ≦ 2, and the sum of the quadratic difference values D2 after entering the interval that is considered to be a linear increase is 2 to a certain constant.
less than or equal to 1'. This judgment is also aimed at more reliable judgment of the linearly increasing section, and utilizes the fact that D2 in the linearly increasing section is almost close to O as shown in Figure 8 (C). . Here, if the sum of the quadratic difference values after entering the linear increasing section is larger than the constant 2, then
Returns without determining that it is a linearly increasing section, but if it is less than the constant 2, it is determined that it is a linearly increasing section and returns 5T.
Proceed to step 107.

In STI'07, the arm cuff internal pressure P c (n-4
1 is stored in the variable SYS, and the systolic pressure determination flag F sv
Set s to 1 cent (ST10B) and return.

On the other hand, the systolic pressure determination flag F svs is 1 at 5 TIOI.
If so, diastolic pressure determination processing from 5T109 to 5T113 is performed. First, in 5T109, it is determined whether the first-order difference (1fi D + +□1. R is on a decreasing trend, and the linear increasing section may have ended, but D I (
. If -1, ≧O, it is determined that the benefit increase section is still continuing, and the process returns without performing any processing.

D. If -0 is negative, then in 5TIIO,
Increment the counter CM by 1. This counter C
N is for counting the number of beats after the pulse wave average ratio R stops increasing, and when it is determined that the count value is 3 or more at the next 5TILL, it is counted as the number of beats after the pulse wave average ratio R stops increasing. It is determined that the process has ended, and the process moves to 5T112, but if it is less than 3, it is assumed that the linearly increasing section has not yet definitively ended, and the process returns without performing any processing.

At 5T112, the cuff internal pressure PCfn-31 three beats ago, that is, when the pulse wave average ratio R has finished the linear increasing section, is stored in the variable DIA, and at 5T113, the diastolic pressure determination flag F is stored.
Set DlA to 1 cent and return.

In the above example, the pulse wave average ratio is obtained when the arm cuff internal pressure is slowly reduced, the linear increasing section of this pulse wave average ratio is detected, and the arm cuff internal pressure corresponding to the starting point is determined as the systolic pressure. The cuff internal pressure corresponding to the end point is determined as the diastolic pressure, but instead of this, the pulse wave average ratio is determined when the cuff internal pressure is slowly pressurized, and the linear decreasing interval of this pulse wave average ratio is calculated. The cuff internal pressure corresponding to the detected starting point may be determined as the diastolic pressure, and the cuff internal pressure corresponding to the ending point may be determined as the systolic pressure.

(f) Effects of the Invention According to this invention, the pulse wave component of the cuff internal pressure is extracted during the slow change process of the cuff internal pressure, the maximum value, the minimum value and the average value of each pulse wave are determined, and Calculate the pulse wave average (IαR = (average value - minimum value) / (maximum value - minimum value)) from these maximum, minimum and average values, detect the linear change section of this pulse wave average ratio, and Since the blood pressure value is determined from the cuff internal pressure at the start and/or end points of the change interval, it is easy to detect the linear change interval of the pulse wave average ratio, compared to conventional oscillometric electronic blood pressure monitors. , accurate measurements can be made.In addition, there is almost no difference in the relationship between pulse wave average ratio and arm cuff pressure between individual subjects, so it is possible to perform measurements with high accuracy for a wide range of subjects.
Correct measurements can be taken.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between arm cuff internal pressure, pulse wave average ratio, and heel for explaining the concept of pulse wave average ratio used in this invention. FIG. 3 is a block diagram of an electronic blood pressure monitor in which the present invention is implemented; FIGS. 4, 5, and 6 are diagrams showing the operation of the electronic blood pressure monitor. FIG. 4 is a main flow diagram, FIG. 5 is a flow diagram showing details of the pulse wave average ratio calculation process in the main flow diagram, and FIG. 6 is a flowchart that does not need to be explained. FIG. 7 is a flowchart showing the blood pressure determination process in detail. FIG. 7 is a diagram for explaining the division of each pulse wave, and FIG. 8 (a) (g)) (c) shows the pulse wave average ratio, FIGS. 9 and 10 are diagrams for explaining blood pressure determination in the conventional oscillometric link method. 1:l15i! Band, 4: Pressure pump, 7: A/D converter, 9: CPU0 3: Exhaust valve, 5: Pressure sensor, 8: Band pass filter, Patent applicant: Tateishi Electric Co., Ltd. Agent, Patent attorney: Shigeru Nakamura 1 to 31 monthly pressure (a) 1 yakuf circular pressure = average blood pressure (b) yoke internal pressure ≦ solitary space (C) Diastolic jE @, diastolic anti-Fl'il q inside L CXi'! a
Direction) - Procedural amendment (spontaneous) Display of the case Patent application No. 264976 filed in 1988 Name of the invention Electronic blood pressure monitor Correction person Relationship with the case Patent applicant address 1 Hanazono Tsuchido-cho, Ukyo-ku, Kyoto Name (294) Tateishi Electric Co., Ltd. Representative: Yoshio Tateishi 0-4, Agent address ■604 1 Kyobu Saiwai Building 5F 7, 3-3 Mibu Kayo Gosho-cho, Nakagyo-ku, Kyoto-shi Contents of amendment (1) No. 5 on page 5 of the specification In the third line, “100%”
The statement was corrected to "100% and SYS was used as the reference." (2) Figure 1 of the drawings is amended as separately attached. 8. List of attached documents (1) Corrected drawings [Figure 1] One or more voluntary amendments

Claims (1)

[Claims] (1) An arm cuff, a pressurizing means for pressurizing the arm cuff, a pressure detecting means for detecting the pressure of the arm cuff, an exhaust means for reducing the pressure of the arm cuff, and a pressure of the pressure detecting means. A pulse wave extraction means for extracting the pulse wave component from the signal, a means for calculating the maximum value, minimum value, and average value of the pulse wave for each beat for the extracted pulse waves, and the formula R=(pulse wave average means for calculating a pulse wave average ratio expressed as (value - minimum value of pulse wave) / (maximum value of pulse wave - minimum value of pulse wave) x 100 [%]; and a slow change process of the pressure of the arm cuff. a linear change section detecting means for recognizing a linearly changing section of the pulse wave average ratio R; and a blood pressure determining means for determining a blood pressure value from the cuff pressure corresponding to the starting point and/or the final point of this linear changing section. An electronic blood pressure monitor characterized by being equipped with.