JPH02147047A - Finger tip volume pulse wave meter - Google Patents

Abstract

PURPOSE:To detect the lowering of blood pressure on an early stage before a shock condition by calculating a lower limit pulse waveheight value from a stored reference pulse waveheight value and outputting an alarm when a present pulse waveheight value goes to be smaller than the lower limit pulse waveheight value. CONSTITUTION:When a sample switch 13 is depressed, a pulse waveheight value signal (j) is taken into a sample-hold circuit 12 as a storing means and the pulse waveheight value at a time, when the sample switch is separated, is held as the reference pulse waveheight value. A reference pulse waveheight value signal is amplified by an amplifying circuit 14, for which a gain is smaller than 1, as a lower limit pulse waveheight value calculating means and goes to be the lower limit signal of the pulse waveheight value. A pulse frequency counting circuit 22 counts the pulse number of a pulse signal (d) and outputs a pulse frequency. The pulse frequency is compared with a pulse frequency upper limit value, which is set to an upper limit value setting switch 24, and a pulse frequency lower limit value, which is set to a lower limit value setting switch 26, respectively by comparators 23 and 25. When the pulse frequency is larger than the upper value and when the pulse frequency is smaller than the lower limit value, the alarm is outputted by an alarm generating circuit 28.

Description

[Detailed Description of the Invention] "Industrial Application Field" This invention is applicable to patients undergoing hemodialysis treatment, Φ stroke after surgery, etc.
The present invention relates to a fingertip plethysmometer suitable for monitoring a drop in blood pressure in patients who may experience hypotensive shock.

"Prior Art" One of the side effects of hemodialysis is the occurrence of hypotensive shock due to insufficient circulating blood volume in the body due to water removal. When the shock is severe, the patient may experience discomfort such as vomiting, convulsions in the limbs, and in the worst case, death. therefore,
It is desirable to detect signs of a drop in blood pressure early and take necessary measures before a syjinx situation develops.

In conventional dialysis, nurses regularly measure pulse rate and blood pressure, and adjust the rate of water removal based on the results to prevent a sudden drop in blood pressure.

``Problem to be Solved by the Invention'' Blood pressure measurement by wrapping a cuff around the upper arm and pulse measurement by counting the pulse are time consuming and place a heavy burden on nurses. In addition, since it has a great effect on the patient, such as interfering with sleep, it is limited to regular use at most once every 30 minutes. With these methods, it was not always possible to quickly detect a drastic drop in blood pressure, and in many cases the drop in blood pressure was only discovered after the patient complained of symptoms of shock.

Not only in dialysis, but in the current medical field, is it the patient's blood? & Circulatory conditions often need to be monitored.

It has been desired to develop a method that can easily and continuously monitor the blood circulation state.

Fingertip plethysmography is widely known as a method for non-invasively and non-invasively testing peripheral blood circulation dynamics. However, since the amplitude of the pulse wave signal varies greatly from person to person, the state of the circulatory system is usually diagnosed by analyzing only the waveform. There are also pulsometers that use the principle of a fingertip plethysmometer, but these only have the function of measuring and displaying the pulse rate.

When the amount of blood circulating decreases, blood vessels constrict to prevent blood pressure from falling, increasing peripheral resistance and reducing peripheral blood flow. The occurrence of hypotensive shock during dialysis varies depending on the case, but the typical process is as follows.

■ Peripheral resistance gradually increases and blood circulation in the periphery decreases.

■ Cardiac output decreases.

■ Pulse rate increases.

■ Blood pressure is maintained within a certain range by ■ ~ ■.

■ It can no longer be maintained, peripheral resistance rapidly decreases, and blood pressure falls.

Depending on peripheral reactivity, blood pressure may gradually decrease from the beginning, may not change much, or may rise over time.
There are various patterns depending on the case. However, −
When boat fishing, blood circulation in the periphery decreases prior to the drop in blood pressure. Therefore, by continuously measuring and monitoring the blood circulation volume in the periphery, it is possible to prevent shock symptoms from occurring.
A drop in blood pressure can be detected at an early stage.

``Means for Solving the Problems'' In the fingertip plethysmometer of the present invention, the difference between the maximum value and the minimum value of the pulse wave signal is calculated as the pulse wave height value by the pulse wave height calculation means, The patient's pulse wave height value at the start of blood circulation state monitoring is stored in the storage means as a reference value. From this reference value, the lower limit of the pulse wave height value is determined by the lower limit pulse wave height value calculation means, and the lower limit pulse wave height value is compared with the current pulse wave height value by the comparison means, and the current pulse wave height value is determined. When the blood pressure falls below the lower limit, an alarm is issued by the alarm generating means as a sign of a drop in blood pressure.
In this way, since a warning is issued based on a relative decrease in pulse wave peak value, individual differences in pulse wave peak value do not matter.

Since the pulse rate is also greatly involved in the mechanism of blood pressure maintenance, it is effective to also use a pulse rate-based alarm in order to increase the reliability of the alarm. In the fingertip plethysmometer of the present invention, the pulse rate is counted by shaping the pulse wave No. 13, and when this value deviates from the range given by the upper and lower limits, which can be set arbitrarily, issue an alarm.

"Example" FIG. 1 shows a block diagram of an embodiment of the invention.

A constant current circuit 1 supplies a constant current to a light emitting diode 2 as a light source. The light emitted from the light emitting diode 2 passes through the fingertip 3 to be measured or is reflected and enters the photodiode 4 as a light receiving element.
excites a photocurrent.

The photocurrent is amplified by a current amplification circuit 5 and converted into a voltage signal. Since this voltage signal is a signal in which a pulse wave signal is superimposed on a direct current, only the alternating current component is extracted and amplified by the alternating current amplifier circuit 6, and the induced noise of the commercial power supply is cut by the low pass filter circuit 7. , a pulse wave signal (a) as exemplified in the time chart of FIG. 2 is obtained. Here, a light emitting diode is used as the light emitting element and a photodiode is used as the light receiving element, but it is also possible to use other elements such as a tungsten lamp for the light emitting element and CdS for the light receiving element. In that case, it is necessary to change the processing circuits before and after the device to match the device.

The pulse wave signal (a) is waveform-shaped by the waveform shaping circuit 17 to become a shaped signal (b), and further integrated by the integrating circuit 18 to produce an integral signal (c) in which only fluctuation components slower than the pulse are extracted. becomes. A comparator 19 compares the shaped signal (b) and the integral signal (c) to obtain a pulse signal (
d).

Furthermore, the one-shot generation circuit 20 generates a pulse signal (
A one-shot pulse synchronized with d) is generated and the sample signal (e) is given to the sample/hold circuit 11, and the reset signal (f), which is slightly delayed from the sample signal by the delay circuit 21, is generated at the maximum peak. It is applied to hold circuit B and minimum peak hold circuit 9.

The pulse wave signal (a) is supplied to the maximum peak hold circuit 8 and the minimum peak hold circuit 9. The maximum peak hold circuit 8 and the minimum peak hold circuit 9, which have been reset by the reset pulse and whose output has become O■, hold the maximum and minimum values of the pulse wave signal (a) and output the maximum value signals (g) and Outputs the minimum value signal (h). In the next differential amplifier circuit 10, the minimum value signal is subtracted from the maximum value signal, and a pulse height signal (i) is output.

The pulse height signal (1) is taken into the sample/hold circuit 11 by the sample signal (e) output in synchronization with the next pulse, and is held as the pulse wave peak value signal (j) until the next sample signal (e). be done.

The reset signal (f) is slightly delayed from the sample signal (e).
) resets the maximum peak hold circuit 8 and minimum peak hold circuit 9 again. By repeating this operation, the pulse wave height value for each pulsation becomes an electric signal (j)
& can be obtained.

By pressing the sample switch 13, the pulse wave peak value signal N) is stored in the sample/hold circuit 1 as a storage means.
2, and the pulse wave peak value when the sample switch is released is held as the reference pulse wave peak value. The reference pulse wave peak value signal is amplified by an amplifier circuit 14, which serves as a lower limit pulse wave peak value calculating means and has a gain smaller than 1, to become a lower limit signal of the pulse wave peak value. Here, if the amplification factor of the amplifier circuit 14 is made variable, the ratio of the lower limit value to the reference can be changed.

The comparator 15 outputs an abnormal signal when the pulse wave peak value signal (j) becomes smaller than the lower limit signal. The timer circuit 16 measures the time during which the abnormal signal is output, and when a certain period of time is exceeded, a pulse wave peak value abnormal alarm is output.

The pulse rate counting circuit 22 calculates a pulse signal (d
) and output the pulse rate per minute. The pulse rate is compared by comparison circuits 23 and 25 with the pulse rate upper limit value set in the upper limit value setting switch 24 and the pulse rate lower limit value set in the lower limit value setting switch 26, respectively, and the pulse rate is greater than the upper limit value. An alarm is output when the pulse rate is lower than the lower limit.

The OR circuit 27 takes the logical sum of the pulse wave high value abnormality alarm, the pulse rate upper limit alarm, and the pulse rate lower limit alarm, and outputs an alarm signal if any one of them occurs.

In response to this, the alarm generation circuit 28 displays an alarm, sounds an alarm, etc., and notifies the user of the occurrence of an alarm.

The OR circuit 27 may be replaced with an OR-AND circuit that takes the logical sum of the pulse rate upper limit alarm and the pulse rate lower limit alarm, and takes the logical product of this logical sum and the abnormal pulse wave height value alarm.

Through the above operations, the pulse wave peak value and pulse rate are continuously measured and monitored, and an alarm is automatically issued when the pulse wave peak value falls below the lower limit or when the pulse rate deviates from the upper and lower limits. emanate.

In the above description, all the processing is performed by hardware, but it is also possible to have a computer perform part of the processing. For example, the pulse wave signal (a) output from the low-pass filter circuit 7 is converted into an A/DI converter, inputted manually into a computer, all subsequent processing is replaced with numerical processing by the computer, and an alarm is displayed on the computer monitor. It may also be possible to output .

"Effects of the Invention" The fingertip plethysmometer according to this invention automatically and continuously measures and monitors the pulse wave height and pulse rate, which are indicators of a patient's blood pressure drop, and detects signs of a blood pressure drop. If this occurs, an alarm will be output to notify doctors and nurses of the danger. By catching signs of a drop in blood pressure early and taking appropriate measures,
This can prevent people from falling into hypotensive shock.

In addition, in conventional dialysis, nurses measure the patient's blood pressure at regular intervals, but by monitoring the patient's peripheral blood circulation status with the fingertip plethysmometer of this invention, blood pressure can be measured without risk. The number of times can be reduced. This reduces the workload of nurses, which helps save labor in medical settings, and also reduces the burden on patients.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a fingertip plethysmometer according to the present invention, and FIG. 2 is a block diagram shown in FIG.
It is a time chart showing signals at points ~(b) on the same time axis.

Claims (2)

[Claims] (1) A light source, a light receiving element that detects the amount of light when the light from the light source is transmitted or reflected from the fingertip, an amplification means that amplifies the pulse wave signal output from the light receiving element, and the amplified pulse wave signal. A pulse wave peak value calculating means for detecting the maximum value and the minimum value of the pulse wave signal and calculating the pulse wave peak value, a storage means for storing the pulse wave peak value serving as a reference for an alarm, and the stored reference pulse value. a lower limit pulse wave height value calculation means for calculating a lower limit pulse wave height value from a wave wave height value; a comparison means for comparing the current pulse wave height value with the lower limit pulse wave height value; A fingertip plethysmometer characterized by comprising an alarm generating means for issuing an alarm when the pulse wave becomes smaller than the pulse wave height. (2) timer means for detecting that a state in which the current pulse wave peak value is smaller than the lower limit pulse wave peak value continues for a certain period of time; and an alarm generating means for issuing an alarm when this state continues for a certain period of time or more; The fingertip plethysmometer according to claim 1, further comprising: