JP3975834B2 - Biological information measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a biological information measuring apparatus for measuring biological information such as blood pressure and pulse wave.
[0002]
[Prior art]
Biological information measuring devices such as blood pressure measuring devices generally measure biological information using the cuff compression method. In this case, the cuff is pressurized until the artery is completely occluded, and then the pressure is gradually reduced to the cuff pressure. The pulse wave signal of the superimposed artery is captured, and the maximum and minimum blood pressures are determined based on the amplitude change or the like, or the pulse wave signal is extracted while being pressurized within a predetermined speed range.
[0003]
At this time, in order to ensure blood pressure determination accuracy in the blood pressure measurement device that determines the blood pressure value in the pressurization process, it is necessary to pressurize at least a section necessary for blood pressure determination within a predetermined speed range. In order to realize the characteristics, pumping feedback control for cuff pressurization is generally performed by measuring the pressurization speed during measurement.
[0004]
[Problems to be solved by the invention]
However, the pressure pulse wave generated from the living body is superimposed on the cuff pressure, and this pulsation component acts as a disturbance in measuring the speed and the like, so at the present time required for feedback control of the pressurization speed. It is difficult to measure the pressurization speed and pressure value, and when the pressurization means (pump) is controlled in response to the pulsation component, the control system falls into an oscillation state and appropriate pressurization control can be performed. The problem of disappearance, the problem of distorting pulse wave information necessary for blood pressure determination or the like, and the resolution of detection on the pressure axis of biological information fluctuate (influence of periodic fluctuation) have occurred. In addition, the control system was sensitive to sudden pressure changes such as pulsation and body movement.
[0005]
Therefore, in order to avoid the influence of the pressure pulse wave superimposed on the cuff pressure, control is performed after the pulsation component is separated from the cuff pressure signal with a low-pass filter, or control is performed only at a relatively low pressure where no pulse wave is generated. The actual situation is that a pump is driven at a predetermined value.
[0006]
However, when a low-pass filter is used, the control system becomes complicated or a time delay occurs. Further, when the control is performed only at a relatively low pressure at which no pulse wave is generated and the pump is driven at a predetermined value thereafter, the stability (linearity) of the pressurizing speed is deteriorated.
[0007]
The present invention has been made in view of the above, and it is possible to accurately measure a blood pressure value and the like without distorting pulse wave information by controlling a cuff pressure on which a pulse wave is superimposed at an appropriate response speed. The purpose is to provide a biological information measuring device.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problems, a biological information measuring apparatus according to the present invention includes a cuff attached to a subject, a pressurizing unit that pressurizes the cuff, a decompressing unit that decompresses the cuff, and a cuff pressure detecting unit that detects the cuff pressure. And a control means for controlling the pressurizing means or the decompression means, and a means for detecting the biological signal of the measurement site from the cuff based on a change in the cuff pressure, wherein the control means has a predetermined time interval. Change amount measuring means for measuring the change amount of the cuff, and a correction amount calculating means for calculating a necessary correction amount from a difference between a result obtained from the change amount measuring means and a predetermined control target value and a predetermined feedback gain And a control value determining means for determining a control value based on the correction amount, and a control value switching means for switching the control value. The predetermined time interval H corresponds to the longest pulse period f to be measured. , It is set to H> 0.5f, and the correction amount calculating means is characterized in that a limit to the correction amount calculated.
[0009]
The correction amount calculation means includes a difference between the upper limit value or lower limit value of the predetermined range and the control target value when the difference between the result obtained from the change amount measurement means and the control target value deviates from the predetermined range. In this case, the correction amount can be suitably used.
[0010]
The correction amount calculation means may calculate the correction amount within a predetermined ratio range with respect to the previous control value.
[0011]
Further, the correction amount calculation means is provided with a control dead zone in which the correction amount is zero when the difference between the result obtained from the change amount measurement means and the control target value is within a predetermined range. May be.
[0012]
The correction amount calculating means may switch the feedback gain at a predetermined pressure.
[0013]
Further, it is preferable that the control value determining means determines the control value within a range not lower than a lower limit value calculated by a predetermined calculation formula defined by the pressure.
[0014]
Further, the control value determining means may switch a predetermined calculation formula defined by pressure at a predetermined voltage.
[0015]
The time interval at which the control value is switched by the control value switching means is preferably the same as or shorter than the interval at which the change amount is measured by the change amount measuring means.
[0016]
Furthermore, it is preferable that the change amount measuring means measures the change amount of the cuff using one or both of the speed and the expected pressure value after a predetermined time has elapsed.
[0017]
Further, the change amount measuring means may use a predetermined number of moving average values of output values obtained from the cuff pressure detecting means when measuring the change amount of the cuff.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on an example of the embodiment . FIG. 2 is a block diagram showing a configuration of the biological information measuring apparatus of the present embodiment. In the cuff 1, a pressurizing means for sending air into the cuff 1 The pump 2, the pressure sensor 3, and the quick exhaust valve 4 are connected. The cuff pressure detected by the pressure sensor 3 is taken into a control circuit (hereinafter referred to as MPU) 5 comprising a microcomputer, and the quick exhaust valve 4 is also controlled to be opened and closed by the MPU 5. The pump 2 is driven by a DC motor, and pressurization control is performed by PWM control of the rotational speed of the DC motor by a pulse signal (duty ratio) from the MPU 5. Further, a display unit 6 and a measurement start button 7 are connected to the MPU 5.
[0019]
The MPU 5 has a function of controlling the pump 2 and the quick exhaust valve 4, a function of taking in the cuff pressure detected by the pressure sensor 3, a function of measuring a pressurization speed at a predetermined time interval, and the pressurization speed. A function for calculating a necessary correction amount from a speed difference between a predetermined pressure control target value and a predetermined feedback gain, and a duty ratio for controlling the rotation speed of the pump 2 is determined based on the correction amount. A function, a duty ratio switching function for switching the duty ratio, and a function of extracting a pulse wave component from the cuff pressure signal to determine a blood pressure value and a pulse value. The blood pressure value and the pulse value are displayed on the display unit 6 after the measurement is completed.
[0020]
Hereinafter, the operation of the biological information measuring apparatus according to the present embodiment will be described. When the cuff 1 is wound around the wrist of the subject and the measurement start button 7 is pressed, the biological information measuring device is turned on and pressurization is started. The cuff pressure is rapidly pressurized to a pressure value (for example, 30 mmHg) that does not affect the measurement of the minimum blood pressure value, and then switched to a slight pressure (for example, 4 ± 1 mmHg / sec) for blood pressure measurement. The MPU 5 sequentially measures the pressurization speed per predetermined time interval H based on the cuff pressure detected by the pressure sensor 3. The time interval H is set so that H> 0.5f with respect to the longest pulse cycle f to be measured. In this embodiment, the longest pulse cycle is 2.0 sec (30 beats / minute), and the time interval H is 1.2 sec.
[0021]
The time interval H is set as described above for the following reason. FIG. 1 shows a part of the cuff pressure signal in a subject whose pulse cycle is 2.0 sec. However, since the pulse wave component is superimposed on the cuff pressure signal, timing synchronized with the peak and valley of the pulse wave (1 sec interval) ), The over- and under-evaluation is repeated with respect to the actual pressurization speed. As a result, the control system falls into an oscillation state, and appropriate pressurization control cannot be performed. There is a fear. In order to avoid such a situation, the time interval H for measuring the pressurization speed is set to H> 0.5f with respect to the longest pulse period f to be measured, so that the influence of periodic fluctuation of the pulse wave is exerted. It is hard to receive. According to the relational expression described above, it is clear that the longer the time interval H, the less affected by the periodic fluctuation of the pulse wave, and the value close to the actual pressurization speed can be measured. .
[0022]
The MPU 5 feeds back the pressurization speed and calculates a necessary control correction amount based on a speed difference from a predetermined pressurization control target value α (for example, 4 mmHg / sec) and a predetermined feedback gain. At this time, if the measured pressurization speed deviates from a preset speed range (for example, 4 ± 2 mmHg / sec), it is considered that the pressure is affected by sudden pressure fluctuations such as body movement and pulsation. The correction amount is calculated using the upper limit value or the lower limit value of the speed range instead of the measured pressurization speed. Specifically, when the measured pressurization speed is 7 mmHg / sec, based on the speed difference between the upper limit value 6 mmHg / sec of the speed range and the pressurization control target value 4 mmHg / sec and the feedback gain. A necessary correction amount is calculated.
[0023]
Further, when the measured pressurization speed is less than 2 mmHg / sec, it is necessary based on the speed difference between the lower limit value of 2 mmHg / sec and the pressurization control target value of 4 mmHg / sec and the feedback gain. A correct correction amount is calculated. As described above, in this embodiment, the control system is not sensitive to sudden pressure fluctuations such as body movement and pulsation, and as a result, the pulse wave information necessary for blood pressure determination is not distorted. A limit is set for the calculated correction amount.
[0024]
After the correction amount is calculated, the MPU 5 determines a duty ratio for controlling the rotation speed of the pump 2 based on the correction amount, and performs switching at the same timing as when the pressurization speed is measured (FIG. 3). reference). T in the figure indicates the duty ratio switching interval. Note that the duty ratio switching may be shorter than the time interval for measuring the pressurization speed as shown in FIG. 4, and in this case, the effect of making it less susceptible to the periodic fluctuation of the pulse wave is maintained. The response speed of the control system can be increased.
[0025]
The MPU 5 further extracts a pulse wave signal from the cuff pressure signal, extracts a pulse wave value from the pulse wave signal, and measures, for example, blood pressure. After determining the blood pressure value, the MPU 5 stops the pump 2 and opens the quick exhaust valve 4 to exhaust, displays the maximum blood pressure value, the minimum blood pressure value, the pulse value, etc. on the display unit 6 and ends the measurement. The method for determining the blood pressure value is not limited to the oscillometric method, and the Korotkoff method may be used.
[0026]
As described above, according to this example, the time interval H for measuring the pressurization speed is set so that H> 0.5f with respect to the longest pulse period f to be measured, and the correction amount is limited. By providing a simple configuration, the cuff pressure with which the pulsating waves are superimposed at an appropriate response speed without being affected by periodic fluctuations due to pulsation or sudden pressure fluctuations due to body movement or pulsation. It becomes possible to control.
[0027]
In the above example, when the measured pressurization speed deviates from the predetermined speed range, the correction amount is calculated based on the upper limit value or the lower limit value of the speed range. Regardless of the pressure or duty ratio, it is provided uniformly in the control pressure range. However, the correction amount may be limited at a predetermined ratio with respect to the previous control value. In this case, if the predetermined ratio is, for example, 5%, the correction amount is calculated within a range of 5% with respect to the duty ratio which is the previous control value. The discharge flow rate of the pump 2 varies depending on the thickness of the wrist, the way of winding the cuff, and the pressure, and even if the correction amount is the same value, the weight for performing the control differs depending on the target and the situation. By changing the limit of the correction amount in accordance with the change in pressure, more appropriate pressure control can be performed.
[0028]
FIG. 5 illustrates another example when the MPU 5 calculates the correction amount. Here, in addition to the limitation of the correction amount, the speed difference between the measured pressurization speed and the pressurization control target value α is a predetermined speed. When it is within the range, a control dead zone B with a correction amount of zero is provided. A in the figure is a control target area. After measuring the pressurization speed during measurement, the MPU 5 calculates the necessary control correction amount from the speed difference from a predetermined pressurization control target value α (for example, 4.0 mmHg / sec). If it is within the speed range (for example, ± 0.5 mmHg / sec), the correction amount is set to zero, and the MPU 5 continuously outputs the previous duty ratio. By providing the control dead zone B in this way, the control system does not react sensitively to minute speed changes or cuff pressure fluctuations that do not affect the blood pressure determination accuracy, thereby further improving control stability. be able to.
[0029]
In this example, the feedback gain for calculating the correction amount may be a constant value in the control pressure range, or may be switched at a predetermined pressure. If such switching is performed, even if the correction amount is uniformly limited in the control pressure range, the pressure is not controlled at low pressure, and the pressurization speed is reduced due to a decrease in control capability due to insufficient gain at high pressure. Can be eliminated, and appropriate control according to the pressure becomes possible.
[0030]
In the above example, when the duty ratio for controlling the rotation speed of the pump 2 is determined, a comparison with the lower limit value of the duty ratio that can be controlled by the pump 2 is performed, so that more stable measurement can be performed.
[0031]
If the controllable flow range of the pump cannot cover the flow range necessary to absorb variations in wrist thickness, cuff winding, etc., for example, the measurement site is narrow and the cuff is tightly wrapped around the measurement site. If the required flow rate is lower than the minimum flow rate that can be controlled by the pump, the pressurization speed will increase and the MPU5 will continue to lower the duty ratio and operate the pump below the minimum drive power. There is a possibility that the pump stops.
[0032]
In order to avoid such a situation, the MPU 5 temporarily determines the duty ratio An for controlling the rotation speed of the pump 2 and then further determines the duty ratio based on the current cuff pressure from a predetermined calculation formula defined by the pressure. A lower limit value Api is calculated, and it is determined whether or not the duty ratio An exceeds the duty ratio lower limit value Api. If this determination is YES, the duty ratio An is output as it is and the previous value is switched. On the other hand, if the determination is NO, the duty ratio lower limit value Api is output and the previous value is switched. Thus, when determining the duty ratio for controlling the rotation speed of the pump 2, the comparison with the lower limit of the duty ratio makes it possible to perform measurement without causing a problem that the pump stops. .
[0033]
The predetermined calculation formula for obtaining the lower limit value of the duty ratio may use one formula in the battery voltage usage range, but switches the calculation formula at a predetermined battery voltage. Also good. Since the lower limit of the duty ratio varies depending on the voltage applied to the pump, and the degree of variation varies depending on the pressure, it is difficult to provide a calculation formula that can be applied to all measurement conditions. Increases the load on the MPU. Therefore, if a plurality of calculation formulas are provided and the calculation formulas are switched at a predetermined battery voltage, the lower limit value of the duty ratio can be obtained appropriately even if the battery voltage, pressure, or the like changes.
[0034]
In the above embodiment, the control correction amount is calculated using the pressurization speed measured at a predetermined time interval. As another embodiment, the predicted pressure value after the predetermined time is set as the control target value. The control correction amount may be calculated from the pressure difference from the actual pressure value by changing the target value with time, and both may be used. Further, when measuring the amount of change in cuff pressure (cuff pressure itself or pressurization speed), a moving average value of a predetermined number (for example, 3 to 5) of cuff pressure signals detected by the pressure sensor 3 is used. In this case, smoothing makes it less susceptible to noise such as pump ripple.
[0035]
【The invention's effect】
As described above, in the present invention, with respect to the influence of periodic fluctuation of pulsation, H> 0 ... For the longest pulse period f to be measured so that the predetermined time interval H is not synchronized with pulsation. Set to be 5f, and body motion, the effects of rapid pressure fluctuations due to pulsation, since the correction amount calculating means is a limit to the correction amount calculated, synchronization and rapidly with pulsation Therefore, the cuff pressure with which the pulse wave is superimposed can be controlled at an appropriate response speed, and at the same time, the pulse wave information necessary for blood pressure measurement can be distorted. It is possible to accurately measure a blood pressure value and the like.
[Brief description of the drawings]
FIG. 1 is an operation explanatory diagram of an example of an embodiment of the present invention.
FIG. 2 is a block diagram of the above.
FIG. 3 is an operation explanatory diagram of another example of the above.
FIG. 4 is a diagram illustrating the operation of still another example of the above.
FIG. 5 is an operation explanatory diagram of another example of the above.
[Explanation of symbols]
1 Cuff 2 Pump 3 Pressure sensor 4 Quick exhaust valve 5 Control circuit (MPU)

Claims (10)

A cuff attached to the subject, a pressurizing means for pressurizing the cuff, a decompressing means for depressurizing the cuff, a cuff pressure detecting means for detecting the cuff pressure, a control means for controlling the pressurizing means or the decompressing means, and the cuff. In the biological information measuring apparatus further comprising means for detecting a biological signal of the measurement site based on a change in cuff pressure, the control means includes a change amount measuring means for measuring a change amount of the cuff at a predetermined time interval, and the change. Correction amount calculating means for calculating a necessary correction amount from a difference between a result obtained from the amount measuring means and a predetermined control target value and a predetermined feedback gain, and control value determination for determining a control value based on the correction amount And a control value switching means for switching the control value, wherein the predetermined time interval H is set to H> 0.5f with respect to the longest pulse period f to be measured, and the correction amount calculation means To the correction amount calculated is a limit biological information measuring apparatus according to claim.   When the difference between the result obtained from the change amount measuring means and the control target value deviates from the predetermined range, the correction amount calculating means determines the difference between the upper limit value or the lower limit value of the predetermined range and the control target value. The biological information measuring device according to claim 1, wherein the correction amount is calculated using   2. The biological information measuring apparatus according to claim 1, wherein the correction amount calculating means calculates a correction amount within a range of a predetermined ratio with respect to the previous control value.   When the difference between the result obtained from the change amount measuring means and the control target value is within a predetermined range, the correction amount calculating means is provided with a control dead zone in which the correction amount is zero. The living body information measuring device according to claim 1 characterized by things.   The biological information measuring apparatus according to claim 1, wherein the correction amount calculating means switches a feedback gain at a predetermined pressure.   2. The biological information measuring apparatus according to claim 1, wherein the control value determining means determines the control value within a range not lower than a lower limit value calculated by a predetermined calculation formula defined by pressure.   2. The biological information measuring apparatus according to claim 1, wherein the control value determining means switches a predetermined calculation formula defined by pressure at a predetermined voltage.   2. The biological information measurement according to claim 1, wherein a time interval at which the control value is switched by the control value switching means is the same as or shorter than a time interval at which the change amount measuring means measures the change amount. apparatus.   2. The biological information measuring apparatus according to claim 1, wherein the change amount measuring means measures a change amount of the cuff using one or both of a speed and an expected pressure value after a predetermined time has elapsed.   2. The living body according to claim 1, wherein the change amount measuring means uses a predetermined number of moving average values of output values obtained from the cuff pressure detecting means when measuring the change amount of the cuff. Information measuring device.

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