JPH0565090B2 - - Google Patents

Description

[Detailed Description of the Invention] "Industrial Application Field" The present invention relates to a body temperature measuring device suitable for use in clinical temperature measurement, particularly continuous measurement of body temperature, measurement of basal body temperature, etc., which is difficult to measure with conventional thermometers. The purpose is to make it possible to obtain continuous body temperature information during daily life.

"Prior Art" Conventionally, body temperature has generally been measured by using a mercury thermometer or an electronic thermometer, and by inserting the thermometer into the armpit or oral cavity. However, it is difficult to measure the area under the armpit or the oral cavity for long periods of continuous measurement. Therefore, conventionally, rectal temperature measurement has been mainly used for long-term body temperature measurement. However, measuring rectal temperature is accompanied by discomfort and is difficult to perform for long periods of time. Other methods include measuring esophageal temperature, tympanic membrane temperature, external auditory canal temperature, and bladder temperature, but these methods are limited to measurements during surgery and are not generally performed because they are uncomfortable or dangerous.

Thermometers using heat flow compensation method (e.g. British patent no.
1354874 and Japanese Patent Application Laid-open No. 111684/1984), it was possible to continuously measure body temperature by attaching a probe to the body surface, and it was the only method that could measure body temperature for a long time without discomfort. .

"Problems to be Solved by the Invention" Among the conventional techniques, thermometers using the heat flow compensation method, which are suitable for long-term body temperature measurement, have the following problems.

(a) A heating element is used to compensate for heat flow, which consumes a large amount of power, making it difficult to use a small battery continuously for long periods of time.

(b) Since a heating element is used, there is a risk of overheating due to malfunction.

(c) Since an electronic circuit is required to control the amount of heat generated, the structure becomes complicated and expensive.

It is an object of the present invention to provide a body temperature measuring device that solves the above-mentioned problems and has performance comparable to that of thermometers using conventional heat flow compensation methods.

"Means for Solving the Problem" According to the present invention, the present invention comprises a probe and a calculation unit, and when the probe is attached to the body surface, the probe has a plurality of temperature sensors that maintain thermal contact with the body surface. and a heat insulating body that covers these temperature sensors, and the heat insulating body has different heat radiation resistance from the positions of at least two temperature sensors to the outside world through the heat insulating body when the probe is attached to the body surface. In other words, the body surface temperatures at these locations with different heat dissipation resistances to the outside world are detected, and the temperature deep within the body surface is estimated from the detected temperatures. The detected temperatures from the plurality of temperature sensors are input to the calculation section, and the calculation section performs an estimation calculation of the deep temperature from the detected temperatures.

In order to improve performance, it is necessary to cover the outside of the heat insulator with a thermally conductive layer with low thermal resistance, to detect the temperature of the thermally conductive layer and use it to estimate deep tissue temperature along with the body surface temperature, and to Various measures such as further covering the outside of the conductive layer with a heat insulating layer and using three or more temperature sensors in contact with the body surface to reduce errors due to poor thermal contact with the body surface are added simultaneously or selectively. It's okay.

"Example" Hereinafter, an example of the present invention will be described using the drawings.

FIGS. 1 and 2 respectively show a cross section and a bottom surface of an example of the probe in the body temperature measuring device of the present invention. The probe is used by being attached to the body surface, and the temperature sensor 11, 1 maintains thermal contact with the body surface when the probe is attached to the body surface.
2 is provided. Therefore, the almost disk-shaped heat insulator 1
3 is provided, and a disc-shaped heat conductive layer 1 is provided at the center of the surface (contact surface) 14 that is to be in contact with the body surface of the heat insulator 13.
5 is attached, and a ring-shaped thermally conductive layer 16 is attached near the periphery of the contact surface 14. Temperature sensors 11 and 12 are attached to the inner surfaces of these thermally conductive layers 15 and 16 in contact with each other, respectively. Therefore temperature sensor 1
1 and 12 are heat insulators 1 except for the heat conductive layers 15 and 16 side
Covered by 3. Also, in this example, the thermally conductive layer 1
The outer surfaces of 5 and 16 are located on the same plane as the contact surface 14.

In this example, the thickness of the heat insulator 13 is greater at the center than at the periphery, that is, the height at the center where the temperature sensor 11 is provided is higher than at the periphery where the temperature sensor 12 is provided. In this way,
When the probe is attached to the body surface 21, the heat radiation resistance from the positions of the temperature sensors 11 and 12 to the outside world is different, that is, in this example, the position of the temperature sensor 11 has a higher heat radiation resistance than the position of the temperature sensor 12. This is the case when the value is increased.

Furthermore, in this example, to improve measurement performance,
Temperature sensors 17 and 18 are disposed on the outer surface of the heat insulator 13 facing the contact surface 14, facing the temperature sensors 11 and 12, respectively, with the heat insulator 13 interposed therebetween. Further, in this example, a heat conductive layer 19 is formed entirely on the surface of the heat insulator 13 opposite to the contact surface 14, covering the temperature sensors 17 and 18.

For the temperature sensors 11, 12, 17, and 18, for example, a negative temperature coefficient resistance element or a transistor that utilizes the temperature characteristics of a PN junction can be used. As the heat insulator 13, a material having low thermal conductivity such as sponge rubber or cork is used. Thermal conductive layer 15,1
For 6 and 19, metals with high thermal conductivity, such as aluminum, copper, and silver, can be used. The thermally conductive layer 1 is designed to maintain good thermal contact between the temperature sensors 11 and 12 and the body surface 21 in contact with the contact surface 14.
5 and 16 have a structure that allows easy contact with the body surface 21, and are bonded to the temperature sensors 11 and 12 with an adhesive having good thermal conductivity. The thermally conductive layer 19 has a sufficient thickness so that the entire thermally conductive layer 19 has approximately the same temperature.

As shown in FIG. 3, a heat insulating layer 22 may be provided on the outside of the heat conductive layer 19 to reduce the influence of outside air, and the heat conductive layer 19 may be embedded in the heat insulating material. The rest is the same as in the case of FIG.

As shown in FIG. 4, a plurality of temperature sensors 12 are arranged around the contact surface 14 in contact with the body surface, and each temperature sensor 12 is adhered to a heat conductive layer 23.
3 is the case where it comes into direct contact with the body surface.
By using the maximum value of the temperatures detected by the plurality of temperature sensors 12 for calculation, errors due to poor thermal contact with the body surface can be reduced.

To measure body temperature, the aforementioned probe is attached to the body surface such as the forehead, chest, abdomen, etc. with the contact surface 14 in close contact, and after a sufficient time has passed, each temperature sensor 11, 12, 17 is attached. , 18 temperatures were measured;
The body temperature is calculated from these measured temperatures. FIG. 5 shows an electrical equivalent circuit of heat flow inside a living tissue and a probe for calculating body temperature. The tissue near the body surface is regarded as a heat transfer layer 24 with almost uniform thermal resistance,
A portion 25 deeper than the heat transfer layer 24 has a uniform temperature TB. Let the respective temperatures of temperature sensors 11, 12, 17, and 18 be T1, T2, T7, and T8.
The thermal resistance values between 2, 11 and 17, and 12 and 18 are R12, R17, and R28, respectively. Further, the thermal resistance values between the deep tissue part 25 and the temperature sensors 11 and 12 are respectively RS and kRs.
5 temperature TB, voltage TB electromotive force, each measurement temperature
Temperature TB considering T1, T2, T7, T8 as measurement voltage
is calculated using the following formula.

TB=(AT2-kBT1)/(A-kB) (1) A=(T1-T7)/R17+(T1-T2)/R12 (2) B=(T2-T8)/R28+(T1-T2)/ R12 (3) Here, R12, R17, R28 and k are constants determined by the structure of the probe. As shown in FIG. 6, each temperature measured by the temperature sensors 11, 12, 17, and 18 is input to the calculation unit 26, calculations (1) to (3) are performed, and the calculation results are displayed on the display unit 27. do. Note that a microcomputer is used as the calculation unit 26, and the temperature sensors 11, 12, 17, 18 are periodically
It is also possible to import digital values into the measured temperature, calculate (1) to (3), and display and record the results.

If the heat conduction layer 19 has good heat conduction and the temperature can be considered uniform, T7=T8, and the temperature sensor 17
Alternatively, either the temperature sensor 18 can be omitted. Further, when a plurality of temperature sensors 12 are used as shown in FIG. 4, the maximum value of the temperatures detected by those temperature sensors 12 is set as T2.

As a simple method of calculating the deep temperature TB, the following linear equation may be used.

TB=T1+α(T1-T2)+β(T1-T7) (4) Here, α and β are constants determined by the structure of the probe. Furthermore, by appropriately designing the structure of the probe, β can be made sufficiently smaller than 1, and in that case, the third term on the right side of equation (4) can be omitted. In other words, TB≒T1+α(T1−T2) (5) When using this formula, temperature sensor 1
7 and 18 can be omitted.

The performance of the body temperature measuring device of this invention was theoretically analyzed using a model that is thermally almost equivalent to a living body.
The area 2-10mm from the body surface is considered to be a uniform heat transfer layer with a thermal conductivity of 0.2-1.6W/mK, and the temperature deeper than that is 37℃. The probe has a diameter of 40 mm and a central thickness of d ₁ .
10 mm, and the thickness d ₂ of the peripheral part is 6 mm, and each heat conductive layer 15, 16, 19 has a sufficiently small thermal resistance and the temperature can be considered to be uniform. Further, the thermal conductivity of the heat insulator 13 is 0.08 W/mK. The outside temperature is 22°C, and the heat transfer from the body surface and the probe surface to the atmosphere uses the values for vertical plate convection heat conduction.
The temperature of each temperature sensor when thermal equilibrium is reached under these conditions is determined using the finite element method, and a constant is determined so that the error is small under conditions close to actual body temperature measurement.
The error E when changing the thickness D and thermal conductivity of the heat transfer layer was calculated. FIG. 7 shows an example of the results obtained when formulas (1), (2), and (3) are used. Here, curve a,
b, c, and d are for the thermal conductivity of the heat transfer layer of 0.2, 0.4, 0.8, and 1.6 W/mK, respectively. Moreover, FIG. 8 shows the results when formula (4) is used. The graphs of curves a, b, c, d correspond to the same conditions as in FIG. In this example, α=1.011 and β=−0.003 in equation (4), and even if equation (5) is used, the error is less than 2%.

Experimentally, on a copper plate at 37°C, the thermal conductivity is approx.
When a 0.2W/mK rubber sheet is placed and a 48mm diameter probe with a structure similar to that shown in Figure 1 is placed,
It was confirmed that the temperature of the copper plate could be calculated with an error of less than 0.2°C when the rubber sheet was 6 mm or less thick at outside temperatures of 25°C and 30°C.

In addition, in experiments using the human body, the diameter was 48 mm.
When the probe is attached to the forehead, the difference from the sublingual temperature is 0.28°C at room temperature of 25°C, and 0.28°C at room temperature of 30°C.
It was 0.16℃.

In the above description, the thickness of the heat insulating body 13 is varied in order to vary the heat radiation resistance from the positions of the temperature sensors 11 and 12 to the outside world, but the thickness may be the same and the comparative conductivity may be varied.

"Effects of the Invention" According to the body temperature measuring device of the present invention described above, the following effects can be expected.

(a) A simple portable continuous body temperature recorder can be realized.

No discomfort like traditional body temperature probes
In addition, since it does not consume large amounts of power like a probe using the heat flow compensation method, by attaching the probe to the head or trunk and carrying a device that operates on a small battery, it can be used for several hours or several hours without restricting physical activity. It is possible to continuously measure body temperature throughout the day.

(b) A thermometer that can easily measure temperature can be realized.

Temperature measurement under the armpit or under the tongue restricts activity during the temperature measurement, and assistance is required for children, the elderly, and critically ill patients. However, according to the body temperature measuring device of the present invention, by simply fixing the probe with a band or adhesive tape, temperature can be measured without restricting activities or requiring assistance.

(c) A highly safe body temperature monitor can be realized.

Body temperature monitors using probes based on the heat flow compensation method use a heating element in the probe, so
Although there is a risk of overheating due to malfunction, the probe of the body temperature measuring device of the present invention does not have a heating element, so there is no risk of overheating. In addition, body temperature monitors using probes based on the heat flow compensation method consume a lot of power, so it is necessary to use a commercial power supply, and there is a risk of electric shock due to poor insulation.However, the probe of the body temperature measurement device of this invention has low power consumption. Since it can be used with a small battery, it does not require commercial power and there is no risk of electric shock.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an example of the probe of the body temperature measuring device of the present invention, FIG. 2 is a bottom view of FIG. 1,
Figure 3 is a longitudinal cross-sectional view of the probe with insulation;
The figure is a bottom view showing an example in which multiple temperature sensors are arranged around the surface of the probe in contact with the body surface.
Fig. 5 is a diagram showing an electrical equivalent circuit of heat flow in deep tissue and inside the probe, Fig. 6 is a block diagram showing an embodiment of the present invention, and Fig. 7 is a diagram using thermal equilibrium temperature distribution analysis results using the finite element method. Figure 5 shows the relationship between body temperature measurement error and the thickness of the skin heat transfer layer when calculated from the equivalent circuit diagram in Figure 5. Figure 8 shows the same relationship as Figure 7 obtained from a simple calculation formula. FIG.

Claims (1)

[Scope of Claims] 1. A probe comprising a plurality of temperature sensors that maintain thermal contact with the body surface when attached to the body surface, and a heat insulator that covers these temperature sensors; and a calculation unit into which each detected temperature is input and calculates the temperature of the deep part of the body surface based on these detected temperatures, and when the probe is attached to the body surface, heat dissipation resistance from at least two positions of the temperature sensor to the outside world is provided. A body temperature measuring device in which the heat insulating body is configured differently.