JPH05329113A - Electronic sphygmomanometer - Google Patents

Abstract

PURPOSE:To prevent the generation of errors owing to variations in blood pressure by converting a pressure change to a capacity change to measure changes in capacity in a blood vessel under a pressure cuff and bag accurately. CONSTITUTION:At the step S21, a variation of a pressure of a pressure cuff and bag is extracted as amplitude value. At the step S22, the amplitude value of the pressure of the cuff and bag extracted is converted to a variation of capacity. The variation at this moment is a changing rate (ml/mmHg) of the capacity at the value of the pressure multiplied by the amplitude value at the pressure value. The changing rates of the capacity at various pressures are stored previously into a ROW or the like. At the S23, the average, maximum and minimum blood pressures are determined by an oscillometric method using a capacity change data thus obtained. At the step S24, the respective blood pressure values determined are shown on a display section as results in measurement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic sphygmomanometer using an oscillometric method for measuring blood pressure based on a change in cuff pressure caused by a change in intravascular volume under the cuff which is superimposed on the cuff pressure.

[0002]

2. Description of the Related Art Conventionally, there is an electronic blood pressure monitor using an oscillometric method. In this electronic sphygmomanometer, the pressure of the cuff wrapped around the blood pressure measurement site is detected by the pressure sensor, and the blood pressure is measured by the change in the detected pressure. Then, as a method of detecting the amount of change in pressure, there are the following methods.

First, the pressure signal from the pressure sensor for detecting the cuff pressure is DC amplified. Then, pass a band pass filter (BPF) (f = 0.5-40Hz), and
After amplification, it is converted into a digital signal by the A / D converter. Then, the CPU or the like calculates the amplitude value of the waveform and sets it as the change amount of the cuff pressure.

The pressure signal from the pressure sensor is DC amplified and then converted into a digital signal by a high resolution A / D converter. There is also a method of calculating the amplitude of the waveform or the area of the waveform from this digital signal and using this as the amount of change in the cuff pressure.

In addition, when a sensor for detecting a pressure change as a change in the capacitor is used, this sensor is used as a CR.
The amount of change in pressure is obtained by incorporating it in an oscillator, detecting a change in frequency, counting this with a frequency counter, and calculating the amplitude or area of the waveform.

The blood pressure value is measured by the oscillometric method using the change amount data of the pressure signal obtained as described above.

[0007]

As described above,
In the above-mentioned conventional electronic blood pressure monitor, the blood pressure value is measured based on the cuff pressure data. However, since the elasticity of the cuff is different between when the cuff pressure is high and when the cuff pressure is low, the relationship of the intracuff pressure change with respect to the intravascular volume change under the cuff is different, and the two are not in a proportional relationship. Therefore, in the above-described conventional measuring method using the electronic blood pressure monitor that measures blood pressure assuming that the change in cuff pressure is proportional to the change in intravascular volume, an error occurs in the measurement. That is, a measurement error occurs depending on whether the blood pressure is high or low. Further, there is a problem that an error occurs in the average blood pressure measured from the maximum point of the intravascular volume change under the cuff.

The present invention has been made in view of the above problems, and converts the pressure change in the cuff into a volume change and accurately measures the intravascular volume change under the cuff to obtain an error in high and low blood pressure. An object of the present invention is to provide an electronic sphygmomanometer that prevents the occurrence of.

[0009]

The electronic sphygmomanometer according to the present invention for achieving the above object has the following configuration. That is, by measuring the blood pressure by pressurizing and depressurizing the cuff wound around the blood pressure measurement site, the change in the cuff pressure signal based on the intravascular volume change under the cuff due to the pulsation superimposed on the cuff pressure is detected. A sphygmomanometer, which stores a volume change characteristic with respect to a change in pressure of the cuff, and converts a change in the cuff pressure signal into a volume change based on the change characteristic stored in the storage means. It comprises a conversion means and a measurement means for measuring the blood pressure value based on the volume change calculated by the conversion means.

[0010]

With the above configuration, the detected change amount of the cuff pressure is converted into the volume change amount, and the blood pressure value is measured based on the obtained volume change amount.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

Generally, when the cuff pressure is high, the cuff is in a stretched state and its elasticity is poor, so that the cuff approaches a rigid body. Therefore, when the cuff pressure is higher than when the cuff pressure is low, the change in the intracuff pressure with respect to the change in the intravascular volume under the cuff becomes large. Further, the change in pressure with respect to the change in the volume inside the cuff is non-linear. And this change in pressure changes its characteristics depending on the cuff material,
It also changes depending on factors such as how the cuff is wrapped, the thickness of the arm, the elasticity of the arm, and the temperature. However, the material of the cuff has the greatest influence on the characteristic of the pressure change with respect to the volume change of the cuff. Therefore, in this embodiment, the characteristic of the volume change with respect to the pressure change of the cuff is obtained in advance and stored in the memory. Then, the measured amount of change in pressure is converted into the amount of change in volume based on the stored characteristic of change in volume with respect to change in pressure. A correct blood pressure measurement value is obtained by using the volume change amount thus obtained. The conversion method in this case may be performed using a conversion formula or a conversion table obtained from the characteristics.

FIG. 1 is a block diagram showing a schematic configuration of an electronic blood pressure monitor according to this embodiment. Reference numeral 1 is a cuff, which is used by being wrapped around the blood pressure measurement site. The cuff 1 has a built-in air bag for blood flow prevention. Reference numeral 2 denotes a pressure sensor, which detects a pressure change in the cuff. Reference numeral 3 denotes a constant speed exhaust valve, which reduces the cuff pressure by exhausting the cuff at a predetermined speed when measuring the cuff pressure. An exhaust valve 4 exhausts air to release the cuff after the measurement of the pulse wave is completed. A pump 5 pressurizes the cuff 1. An air pipe 6 connects the cuff 1, the pressure sensor 2, the constant speed exhaust valve 3, the exhaust valve 4, and the pump 5. A constant current source 7 is a power source for driving the pressure sensor. Reference numeral 8 denotes an amplifier, which amplifies the signal from the pressure sensor 2 by DC. An A / D converter 9 converts the signal output from the amplifier 8 into a digital signal.
Reference numeral 10 denotes a CPU, which performs comprehensive control of the electronic blood pressure monitor. Reference numeral 11 denotes a ROM, which stores various processing programs executed by the CPU 10, a volume change characteristic table with respect to the cuff pressure, and the like. A RAM 12 stores measurement data such as cuff pressure and measurement results. A display unit 13 displays a blood pressure measurement result and the like. Reference numeral 14 is a drive unit, which drives the exhaust valve 4 and the pump 5 according to a command from the CPU 10. 15 is a system bus,
The above-described components are connected to each other, and data can be exchanged between the components.

Next, the operation of the electronic blood pressure monitor having the above-mentioned structure will be described.

FIG. 2 is a flow chart showing the procedure for measuring the cuff pressure by the electronic blood pressure monitor. This process is started by setting the cuff 1 at the blood pressure measurement site and pressing the blood pressure measurement start switch.

First, in step S11, initialization such as setting the cuff pressure value to zero is performed. Next, in step S12, the pump 5 is driven by the drive unit 14 to start pressurizing the cuff 1. In step S13, it is determined whether the pressure value of the cuff 1 detected by the pressure sensor 2 has exceeded a predetermined value. Here, the predetermined value is a value predicted as a systolic blood pressure value that can be taken by a human, and this value is stored in the ROM 11 in advance. In step S13,
If the pressure value of the cuff 1 (cuff pressure) does not exceed the predetermined value, the process returns to step S12 to continue pressurizing the cuff. On the other hand, if the cuff pressure exceeds the predetermined value, the process proceeds to step S14, and the measurement of the pulse wave by the cuff pressure is started.

In step S14, the pump 5 is stopped by the drive unit 14 and constant speed exhaust by the constant speed exhaust valve 3 is started. The constant speed exhaust reduces the cuff pressure, and in the process of reducing the pressure, the cuff pressure is measured in step S15. In step S15, the pressure sensor 2 detects changes in the cuff pressure due to depressurization and pulsation of the measurement site. The pressure signal obtained from the pressure sensor 2 is DC-amplified by the amplifier 8, converted into a digital signal by the high resolution A / D converter 9, and stored in the RAM 12.

In step S16, it is determined whether the cuff pressure is below the lower limit value. The lower limit value is a value predicted as the lowest blood pressure value that can be taken by humans. If the cuff pressure is not below this lower limit, step S15.
Then, the process described above, that is, the measurement of the cuff pressure is repeated. If the cuff pressure is below the lower limit, the process proceeds to step S17, the exhaust valve 4 is driven by the drive unit 14 to release the cuff 1, and this processing is ended.

Next, a method of calculating the volume change amount from the cuff pressure data obtained by the above-mentioned cuff pressure measurement and determining the blood pressure value will be described with reference to FIGS.

FIG. 3 is a flow chart showing the processing procedure for determining the blood pressure value of the electronic blood pressure monitor according to this embodiment. Also, FIG.
FIG. 6 is a diagram showing cuff pressure data and cuff volume data stored in the RAM 12. Further, FIG. 5 is a diagram showing the characteristic of the cuff volume change stored in the ROM 11 with respect to the cuff pressure change.

First, in FIG. 3, the amount of change in the cuff pressure is extracted in step S21. Here, the amount of change in the cuff pressure is divided into a change associated with decompression by the constant velocity exhaust valve and a change associated with pulsation, and the amount of change in cuff pressure due to pulsation is represented by its amplitude value. The amount of change in the extracted cuff pressure is RA
It is stored in M12. The data at this time is shown in a graph as shown in FIGS. 4 (a) and 4 (b). Where (a)
Represents the change data of the cuff pressure due to the pressure reduction by the constant velocity exhaust valve, and (b) shows the amplitude value data of the change of the cuff pressure due to the pulsation.

Next, in step S22, the amount of change in the cuff pressure due to the pulsation (that is, the cuff pressure amplitude value) is converted into a volume change value and stored in the RAM 12. In this conversion, the characteristic of the cuff volume change with respect to the cuff pressure change shown in FIG. 5 is used to convert the cuff pressure amplitude value shown in FIG. 4B into a volume change amount. The conversion method is as follows: The volume change rate (ml / mmHg) at the pressure value for which the amplitude value is obtained is obtained from the characteristic data of FIG. 5, and this volume change rate is calculated as the amplitude value (m
It is converted to the volume change value (ml) by multiplying by mHg). The cuff volume change data obtained by this conversion process is shown in FIG.

Then, in step S23, blood pressure value extraction is executed using this cuff volume change data. First, the change in the cuff volume is maximum when the pressure difference between the blood vessel inside and outside the cuff is zero, and this pressure becomes the average blood pressure, so the maximum point of the amount of data change is the mean blood pressure (MEAN). Next, assuming that the volume change amount at this time is P (ml), the point immediately before the volume change amount falls below P × α (0 <α <1) is searched from this mean blood pressure position. The maximum blood pressure point (SYS.) Is used. In addition, searching from the position of mean blood pressure to the lowest blood pressure side, P × β (0 <β <
The point just before falling below 1) is the lowest blood pressure point (DI
A. ). Here, α and β are constants for obtaining the amount of change in volume at the highest and lowest blood pressure values, respectively, and are stored in the ROM 11 in advance.

As the blood pressure value extraction method, the above α,
There are various methods other than determining the blood pressure value using β.
For example, a method in which a point where the change amount suddenly increases from the average blood pressure value is set as the maximum blood pressure point, and a point where the change amount is broader than the average blood pressure is detected as the minimum blood pressure is detected. There is also.

Finally, in step S24, the obtained blood pressure value is displayed on the display unit 13, and this processing ends.

The difference between the average blood pressure point obtained by the conventional cuff pressure and the average blood pressure point obtained by the electronic sphygmomanometer of this embodiment will be described. For example,
Since the maximum point of the change in the cuff pressure amplitude value shown in FIG. 4B is 144 mmHg, the average blood pressure is calculated to be 144 mmHg. However, when the average blood pressure is obtained from the volume change value ((c) in FIG. 4), the maximum point of the volume change value is 110 mmHg. Needless to say, the point determined based on this change in volume is an accurate measurement value that better reflects the change in blood vessel volume under the cuff. Since the correct mean blood pressure point can be detected, the systolic blood pressure and the diastolic blood pressure point determined by the size of the mean blood pressure point are also accurate values.

As described above, according to the electronic sphygmomanometer of the present embodiment, by correcting the non-linearity between the change in blood vessel volume under the cuff and the change in the cuff pressure due to the cuff pressure, it is possible to determine whether the cuff pressure is large or small. Instead, it is possible to correctly detect the volume change under the cuff based on the detected change in the cuff pressure, and it is possible to accurately measure the blood pressure regardless of whether the blood pressure is high or low.

In order to cope with the measurement error that occurs when the systolic blood pressure is high and when the systolic blood pressure is low, the multiplication factor α for obtaining the threshold value of the systolic blood pressure point is changed according to the systolic blood pressure value, and the The method of data processing is adopted.
Even in this case, since the correction is performed according to the characteristics of the used cuff, more accurate measurement is possible.

In the above embodiment, the characteristic data of pressure-volume change of the cuff to be used is stored in the ROM 11 and the pressure change is converted into volume change using this characteristic data, but the present invention is not limited to this. .. It is also possible to store characteristic data of pressure-volume changes of a plurality of types of cuffs in advance and switch the characteristic data to be used according to the cuff to be used.

Further, in the configuration of the above embodiment, the pump 5 is a pump such as a piston pump that can determine the amount of air to be sent, and the characteristic data of the pressure-volume change of the cuff is measured when the cuff is pressurized. It is possible. That is, the change characteristics of the cuff pressure and the change in the cuff volume as shown in FIG. 5 are measured from the amount of air sent into the cuff 1 at the time of pressurizing the cuff, the cuff pressure obtained from the pressure sensor 2, and the compression rate. You can Here, the compression rate is stored in the ROM 11 in advance. In this way, by using the characteristic data measured during pressurization, the type of cuff used,
It is possible to perform measurement while correcting the winding method, the elasticity of the arm, the temperature, and the like, and it is possible to further improve the blood pressure measurement accuracy.

[0031]

As described above, according to the electronic sphygmomanometer of the present invention, it is possible to convert a pressure change into a volume change and to accurately measure the intravascular volume change under the cuff, which results in an error in high and low blood pressure. Is prevented and the measurement accuracy is improved.

[0032]

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an electronic blood pressure monitor of the present embodiment.

FIG. 2 is a flowchart showing a processing procedure of cuff pressure measurement of the electronic blood pressure monitor of the present embodiment.

FIG. 3 is a flowchart showing a data processing procedure for determining a blood pressure value.

FIG. 4 is a diagram showing a relationship between cuff pressure data and volume change data obtained by conversion.

FIG. 5 is a diagram showing a relationship between a change in cuff pressure and a change in cuff volume.

[Explanation of symbols]

 1 cuff 2 pressure sensor 3 constant speed exhaust valve 4 exhaust valve 5 pump 8 amplifier 9 A / D converter 10 CPU 11 ROM 12 RAM 13 display section 14 drive section 15 system bus

Claims (1)

[Claims] 1. A blood pressure is detected by pressurizing and depressurizing a cuff wrapped around a blood pressure measurement site, thereby detecting a change in a cuff pressure signal based on a change in intravascular volume under the cuff due to a pulsation superimposed on the cuff pressure. An electronic sphygmomanometer for measuring, wherein a storage means for storing a change characteristic of a volume with respect to a change in the pressure of the cuff, and a change in volume of the cuff pressure signal based on the change characteristic stored in the storage means. An electronic sphygmomanometer, comprising: a conversion unit that converts into the following: and a measurement unit that measures a blood pressure value based on the volume change calculated by the conversion unit.