JPS62167532A - Heating type blood flowmeter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention is a blood flow meter that measures the amount of blood flowing through blood vessels. , relates to a heating blood flow meter that measures blood flow by measuring the heating power necessary to maintain the heating member at a constant temperature against the cooling effect of subcutaneous blood flow.

[Prior Art] When diagnosing a patient's pathological condition, it is meaningful to know the amount of blood flowing through the patient's blood vessels.

Conventionally, electromagnetic induction method, nuclear magnetic resonance method, heated body cooling effect method, etc. have been used as methods to measure blood flow. It is an invasive method and has the disadvantage that the equipment is expensive. Further, the nuclear magnetic resonance method also has disadvantages in that its equipment is expensive, and the heated body cooling effect method is also an invasive method.

In contrast, a heating member is attached to the subject's skin surface,
By maintaining the above-mentioned heating member at a constant temperature against the cooling effect of subcutaneous blood flow and measuring the heating power required at that time, the heating member can be heated within a certain range under the skin of a specific part of the bloodstream, more specifically, by measuring the heating power required at that time. A heating type blood flow meter has been proposed that measures the local circulating blood flow, which is the sum of the blood flow in the blood flow area. When this heating type blood flow meter is used, it is non-invasive, has a simple structure, and is inexpensive.

[Problems to be Solved by the Invention] When measuring blood flow with the above-mentioned heating type blood flow meter, the cooling factor of the heating member attached to the skin surface includes the local circulating blood flow to be measured. In addition, (a) heat dissipation by static heat conduction to human tissue near the heating member attachment part, (b) heat dissipation from the sensor part including the heating member into the air, and (c) heat dissipation between the sensor part and the measurement part. There is heat radiated into the air from the sensor lead wires that connect the two, and the cooling effect of these three types of heat radiation causes measurement errors. Among these, static heat conduction (a) has small differences between individuals and measurement sites, and its value can be determined by stopping blood flow at peripheral sites due to constriction, so it is easy to compensate. On the other hand, the heat dissipated into the air from the sensor parts and sensor lead wires in (b) and (c) fluctuates depending on the indoor temperature and air flow, and therefore is not easy to compensate for.

By the way, in order to improve the measurement accuracy of this heating type blood flow meter, it is known that the sensor part is covered with a heat insulating material (
JP-A-55-88750, JP-A-55-1332
However, even with this, there is some heat radiated into the air from the sensor section and the sensor lead wire, and the amount of heat radiated varies depending on the ambient temperature, resulting in measurement errors.

There are also known sensors in which the sensor part is covered with a temperature-controlled metal jacket (Japanese Unexamined Patent Publication Nos. 55-88749 and 1988-88737); The structure is complicated by the need for a device to heat the jacket and control the temperature, and although the amount of heat radiated from the sensor part can be made constant, the amount of heat radiated from the sensor lead wire cannot be made constant. A constant error remains.

This invention was made to solve the above-mentioned conventional problems, and has a simple structure that accurately compensates for measurement errors caused by the amount of heat radiated into the air from the sensor section and sensor lead wire of a heating blood flow meter. The purpose is to

[Means for Solving the Problem] As a result of various considerations and experiments, the inventors determined the temperature of the outer surface of the heat insulating cover that covers the sensor section and the heating power required to maintain the heating member at a constant temperature. We discovered that there is a proportional (linear) relationship between the two.

This invention was made based on the above fact, and detects the temperature of the outer surface of the heat insulating cover that covers the sensor section, and detects the sensitivity indicating the rate of change in the heating power of the heating member with respect to the temperature of the cover. From this sensitivity, cover temperature, and heating power, temperature compensation for the above heating power is performed based on a linear calculation formula for the cover temperature. It is configured to calculate the blood flow heating power that supplies the amount of heat taken away by the blood flow.

[Function] According to the above configuration, three error factors when measuring blood flow:
In other words, (a) heat dissipation due to static heat conduction to human tissue near the heating member attachment part, (b) heat dissipation from the sensor part including the heating member into the air, and (c) heat dissipation between the sensor part and the measurement part. Since all measurement errors due to heat radiation into the air from the sensor lead wire connecting the sensor are compensated for, an accurate blood flow heating power, that is, an accurate blood flow rate can be obtained. Further, a heating device for the cover becomes unnecessary. Furthermore, the blood flow heating power measurement section can be configured by a combination of simple arithmetic circuits.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 shows a blood flow sensor, and 11 is a cylindrical thermally conductive heating member that applies heat to the subject from the skin surface 12, and is made of silver, copper, aluminum, or an alloy thereof. . This heating member 11 has grooves 13 on its outer periphery.
A heating body 14 made of a heating wire for heating the heating member 11 is wrapped around the heating member 11.
A first temperature detection element 15 that detects the temperature of 1 is attached.

The heating member 11, the heating body 14, and the first temperature detection element 15 are molded with a shaped body 16 made of epoxy or Teflon to form an integrated sensor part 17 in order to shape the outer shape. The sensor portion 17 is surrounded by a polyacetal heat insulating cover 18, except for the contact portion 11a of the heating member 11 with the skin surface 12.

Here, an air layer 19 is provided between the cover 18 and the sensor section 17 in order to improve the heat insulation effect. The cover 18 has a substantially cylindrical shape, and on its upper surface,
A second temperature detection element 21 that detects the temperature of the outer surface of the cover 18 is attached. 22 is a sensor lead wire that connects the sensor section 17 and the measurement section 23.

The first temperature detection element 15 and the second temperature detection element 21 are made of a thermistor, a platinum resistor, or the like.

At the time of measurement, the sensor section 17 and cover 18 are attached to the skin surface 12 with a thin double-sided adhesive tape 22.

Next, the measurement principle of this invention will be explained.

First, put the sensor shown in Fig. 1 into a thermostat, and heat the heating member 1.
The heating power required to heat the heating member 11 was measured when the temperature of the thermostatic oven was changed, that is, when the ambient temperature was changed while the heating member 11 was maintained at a temperature of 43° C. and 144° C., respectively. The results are shown in FIG. From the figure, it can be seen that there is a linear relationship between the ambient temperature and the heating power, and even if the set temperature of the heating member 11 changes, the slope remains the same and moves in parallel. This is generally a transition from a hot body (sensor) to a cold body (
It is easy to understand that the amount of heat transferred to the surrounding air is proportional to the temperature difference between the two.

Next, the same sensor was attached to the palm of the hand and placed in a thermostatic oven, the heating member 11 was kept at 43°C, the temperature of the thermostatic oven, that is, the ambient temperature was changed, and the cover 18 at that time was changed.
The relationship between temperature and heating power under steady blood flow and hemostatic conditions was investigated. The results are shown in FIG. From the figure, it can be seen that there is a linear relationship between heating power and cover temperature.

This fact is an important basis of this invention. The reason why the above linear relationship was obtained is considered to be because the temperature of the cover 18 and the ambient temperature are in a proportional relationship, considering the results in FIG. 2 as well. If the temperature of the cover 18 is measured using a sensor in which the heating power and the cover temperature are in a proportional linear relationship, measurement errors due to heat radiation can be easily corrected.

Therefore, assuming that the heating power for keeping the heating member 11 at a constant temperature is H, H is expressed by the following equation.

H=-AT+B+H(f)...(1)A
: Temperature coefficient of heating power B: Amount of heat dissipated into the air at a temperature of 0°C H (f): * Current heating power Here, A above corresponds to the sensitivity indicating the rate of change in heating power with respect to cover temperature. Although the size varies depending on the location of the heating member on the human body and individual differences in the amount of heat dissipated due to static heat conduction to the human tissue near the location on which the heating member is attached, it is approximately -6 ~-8mw
/'O. This A measures the heating power and cover temperature under two different ambient temperatures (for example, indoors and in a higher temperature oven) by attaching the sensor to the subject's skin surface, and then calculates the difference between the heating power and the cover temperature. , ΔH/ΔT. In addition, the amount of heat radiated into the air in B above is the previously mentioned (b) amount of heat radiated from the sensor section 17 into the intake air, and (c) the amount of heat radiated into the air.
It includes both the amount of heat released from the sensor lead wire 22 into the intake air. The blood flow heating power of H(f) above refers to the power taken away by the blood flow out of the heating power.

For example, if the cover temperature at a certain ambient temperature (for example, room temperature) and the heating power in the chemical m state are Tl and Hl, respectively, then H(f) = O when hemostasis, so equation (1) is as follows. -1,=-AT, +H Therefore, B -A Tl + Hl Substituting this into equation (1), H=-A (T-TI) +H, +H(f) ・
...(2) Also, the cover temperature at the above ambient temperature, the heating power in the steady blood flow state, and the blood flow heating temperature are respectively T2
．． H2, Hl(f), equation (1) becomes H2=
-A Tl +H+ Hl(f) Therefore, B = A T2+ H2-Hl(f) Substituting this into equation (1), H=-A (T-T2) +H2-H, (f) +H(
f)...(3) It is expressed as follows.

Therefore, by using equation (2) or equation (3), it is possible to correct the measurement error due to heat radiation, that is, to compensate for the temperature of blood flow measurement.

FIG. 4 shows an example of the measuring section 23 that performs temperature compensation using the above equation (2).

In the figure, a first temperature detection element 15 that detects the temperature of the heating member 11 shows a resistance change proportional to the temperature. From this resistance change, the temperature To of the heating member 11 is detected by the temperature measuring bridge 31 having a well-known circuit configuration. Upon receiving a temperature detection signal representing To from the temperature measuring bridge 31,
A heating control circuit 33 of the heating circuit 32 generates a control signal;
The driving circuit 34 is driven to supply heating power to the heating body 14 so that the temperature To is kept at a constant value.

The heating control circuit 33 is, for example, a so-called PID (Propor-
tional Integral Differer+
cial) control system. The drive circuit 34
The heating power outputted by the power measuring device 35 is detected by a power measuring device 35 consisting of a square amplifier having a well-known circuit configuration.

On the other hand, the second temperature detection element 21 attached to the cover 18
From the resistance change, the temperature measuring bridge 36 and the integrating circuit 37
After that, the temperature T of the cover 18 is detected. The integration circuit 37 determines the responsiveness of heating power to changes in ambient temperature;
This is to correct the difference in response from the second temperature detection element 21. Generally, the response time of the second temperature detection element 21 is shorter, so the signal from the second temperature detection element 21 It is used to give a time constant to

38 is a sensitivity setting circuit, which sets the sensitivity (temperature coefficient) A determined in advance.
is set using an external dial. The sensitivity setting circuit 38 and the temperature detection signal representing the temperature T from the integrating circuit 37 are input to a multiplier circuit 40 of the temperature compensation circuit 39, and a signal representing AT is output. This signal is input to the zero point adjustment circuit 41.

In the zero point adjustment circuit 41, -
A bias corresponding to ATI-H is generated, and this -AT
It is adjusted so that I-Hl is the zero point.

In other words, the zero point adjustment is performed in accordance with the ambient temperature.
Therefore, from the zero point adjustment circuit 41, A (T-Tl
)-H, is output. This signal is input to the correction calculation circuit 42 and added to the signal representing the heating power H from the power measuring device 35 to obtain H0A (T-TI).
-HI(-H(f)) is obtained.

The blood flow heating power H(f) thus obtained corresponds accurately to the blood flow rate.

Unlike the above embodiment, when formula (3) is used, the bias value of the adjustment circuit 41 is simply -AT unity Hλ+ H, (f), and the circuit configuration may be completely the same.

Since the present invention has the above-described configuration, it has several advantages.

(1) Non-invasively, the sensor part 17 is attached to the skin surface 12 in FIG.
Blood flow can be measured easily and without causing pain to the subject by simply pasting the is done with high precision.

(3) Since there is no need for a device to heat the cover and control the temperature to a constant temperature, the structure is simplified.

(4) Commercially available transcutaneous blood oxygen concentration sensor (Unexamined Japanese Patent Publication No. 1983-
88749) can be used as is as the sensor section 17, it is inexpensive, and it is possible to simultaneously measure blood oxygen concentration and blood flow.

(5) The sensitivity A input to the sensitivity setting circuit 38 by external operation can be easily determined by measuring the heating power H and the cover temperature T at two ambient temperatures in advance, as described above. Easy to operate.

[Effects of the Invention] As explained above, according to the present invention, blood flow can be measured with high precision, and the structure is simple and operation is easy.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing the sensor section of a blood flow meter according to an embodiment of the present invention, FIGS. 2 and 3 are characteristic diagrams showing the temperature characteristics of the sensor of the same embodiment, and FIG. FIG. 2 is a system diagram showing the overall configuration of an example. 11...Heating member, lla...Contact part, 12...
Skin surface, work 4... Heating body, 15... First temperature detection element, 17... Sensor section, 18... Heat insulating cover, 21... Second temperature detection element, 22 ...sensor lead wire, 23...measuring section, 32...heating circuit, 3
5... Power measuring device, 38... Sensitivity setting circuit, 39.
...Temperature compensation circuit, A...Sensitivity.

Claims (1)

[Claims] (1) A thermally conductive heating member attached to the skin surface of the subject, a heating body that heats this heating member, and heating the heating member with the heating member leaving a contact area with the skin surface. an insulating cover that covers the body; a first temperature detection element that detects the temperature of the heating member; and a temperature detection signal from the first temperature detection element to maintain the heating member at a constant temperature. a heating circuit that supplies heating power to the heating body so as to hold the heating body; a power measuring device that measures the power; a second temperature detection element that detects the temperature of the outer surface of the cover; A sensitivity setting circuit that sets the sensitivity indicating the rate of change in the heating power by external operation, a sensitivity signal from the sensitivity setting circuit, a cover temperature signal from the second temperature detection element, and a signal from the power measuring device. By receiving the heating power signal and performing temperature compensation on the heating power signal based on a linear calculation formula with respect to the cover temperature, the blood flow heating power that supplies the amount of heat taken away by the blood flow out of the heating power is calculated. A heating type blood flow meter equipped with a temperature compensation circuit.