Temperature Measurement Device and Temperature Measurement Method

Abstract

An embodiment is a temperature measuring device including a sensor that measures the temperature of a skin surface of a living body and a heat flux on the skin surface, a time constant calculation unit that calculates a time constant of changes in the temperature over time on the basis of the measurement result of the temperature, a thermal resistance derivation unit that derives the thermal resistance of the living body on the basis of the time constant, and a temperature calculation unit that calculates the internal temperature of the living body on the basis of the temperature of the skin surface and the heat flux on the skin surface measured by the sensor and the thermal resistance derived by the thermal resistance derivation unit.

Claims

1.-4. (canceled)

5. A temperature measuring device comprising: a sensor configured to measure a temperature of a surface of a subject and a heat flux on the surface; a time constant calculator configured to calculate a time constant of changes in the temperature over time based on a measurement result of the temperature; a thermal resistance deriver configured to derive thermal resistance of the subject based on the time constant; and a temperature calculator configured to calculate an internal temperature of the subject based on the temperature, the heat flux, and the thermal resistance.

6. The temperature measuring device according to claim 5, further comprising a storage device configured to store in advance a calibration table in which thermal resistance corresponding to the time constant is registered for each time constant.

7. The temperature measuring device according to claim 6, wherein the thermal resistance deriver derives the thermal resistance by acquiring, from the calibration table, a value of thermal resistance corresponding to the time constant calculated by the time constant calculator.

8. The temperature measuring device according to claim 5, wherein the time constant calculator is configured to calculate the time constant immediately after the sensor is attached to the surface of the subject.

9. The temperature measuring device of claim 5, further comprising: a display device to display the calculated internal temperature.

10. A temperature measuring method comprising: measuring a temperature of a surface of a subject; calculating a time constant of changes in the temperature over time based on a measurement result of the temperature; deriving thermal resistance of the subject based on the time constant; measuring a heat flux on the surface of the subject; and calculating an internal temperature of the subject based on measurement results of the temperature and the heat flux and the calculated thermal resistance.

11. The temperature measuring method according to claim 10, further comprising: storing in advance a calibration table in which thermal resistance corresponding to the time constant is registered for each time constant.

12. The temperature measuring method according to claim 10, wherein the thermal resistance is derived by acquiring, from a calibration table stored in advance, a value of thermal resistance corresponding to the calculated time constant.

13. The temperature measuring method according to claim 10, further comprising: outputting the calculated internal temperature to a display device.

14. The temperature measuring method according to claim 10, further comprising: sending the calculated internal temperature to a communication device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a block diagram illustrating the configuration of a temperature measuring device according to an embodiment of the present invention.

[0013] FIG. 2 is a diagram illustrating a thermal equivalent circuit model of a living body and a sensor according to the embodiment of the present invention.

[0014] FIG. 3 is a diagram illustrating an example of the relationship between a time constant of changes in a skin surface temperature over time immediately after sensor attachment and the thermal resistance of a living body.

[0015] FIG. 4 is a flowchart for explaining operations of the temperature measuring device according to the embodiment of the present invention.

[0016] FIG. 5 is a block diagram illustrating an example of the configuration of a computer that implements the temperature measuring device according to the embodiment of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram illustrating the configuration of a temperature measuring device according to an embodiment of the present invention. The temperature measuring device includes a sensor 1 that measures a temperature T.sub.skin of a skin surface of a living body 10 (subject) and a heat flux H.sub.skin on the skin surface, a storage unit 2 that stores in advance a calibration table in which thermal resistance R.sub.Body of the living body 10 corresponding to a time constant τ of changes in the temperature T.sub.skin over time is registered, a time constant calculation unit 3 that calculates the time constant τ of the changes in the temperature T.sub.skin over time on the basis of the measurement result of the temperature T.sub.skin, a thermal resistance derivation unit 4 that derives the thermal resistance R.sub.Body of the living body 10 on the basis of the time constant τ, a temperature calculation unit 5 that calculates a deep body temperature T.sub.core (internal temperature) of the living body 10 on the basis of the temperature T.sub.skin, the heat flux H.sub.skin, and the thermal resistance R.sub.Body, and a calculation result output unit 6 that outputs the calculation result of the deep body temperature T.sub.core.

[0018] The sensor 1 includes a thermal insulation member 100, a temperature sensor 101 disposed on a surface of the thermal insulation member 100 in contact with the skin of the body 10, and a temperature sensor 102 disposed on a surface of the thermal insulation member 100 on a side opposite to the surface in contact with the skin. By the temperature sensor 101, it is possible to measure the temperature T.sub.skin of the skin surface of the living body 10. Furthermore, it is possible to derive the heat flux H.sub.skin of the skin surface on the basis of a difference between the temperature T.sub.skin of the skin surface and a temperature T.sub.upper measured by the temperature sensor 102. The sensor 1 is attached to the skin surface of the living body 10 by, for example, a thermally conductive double-sided tape. The configuration illustrated in FIG. 1 is an example, and the sensor 1 may have a configuration different from that illustrated in FIG. 1.

[0019] FIG. 2 is a diagram illustrating a thermal equivalent circuit model of the sensor 1 and the living body 10. In FIG. 2, T.sub.upper denotes the temperature of an upper surface of the sensor 1 on a side opposite to the surface in contact with the skin of the living body 10, T.sub.Air denotes an outside air temperature, R.sub.Body denotes the thermal resistance of the living body 10, R.sub.sensor is the thermal resistance of the sensor 1, R.sub.Air denotes the heat resistance of outside air, C.sub.Body denotes the heat capacity of the living body 10, and C.sub.sensor denotes the heat capacity of the sensor 1.

[0020] The changes T.sub.skin(t) in the temperature of the skin surface of the living body 10 over time immediately after sensor attachment and the changes T.sub.upper (t) in the temperature of the upper surface of the sensor 1 over time immediately after the sensor attachment are expressed as follows by using the outside air temperature T.sub.Air, the deep body temperature T.sub.Core of the living body 10, the thermal resistance R.sub.Body of the living body 10, the thermal resistance R.sub.sensor of the sensor 1, the thermal resistance R.sub.Air of the outside air, the heat capacity C.sub.Body of the living body 10, and the heat capacity C.sub.sensor of the sensor 1.

[00001]$\begin{array}{cc}\left[\mathrm{Math}.1\right]& \\ T_{Skin}\left(t\right)=T_{Core}-R_{\mathrm{Body}}\left(\frac{T_{Skin}\left(t\right)-T_{\mathrm{Upper}}\left(t\right)}{R_{Sensor}}+C_{\mathrm{Body}}{T}_{\mathrm{Skin}}^{\prime }\left(t\right)\right)& \left(2\right)\end{array}$$\begin{array}{cc}{T}_{\mathrm{Upper}}\left(t\right)=T_{Skin}\left(t\right)-R_{\mathrm{Sensor}}\left(\frac{T_{\mathrm{Upper}}\left(t\right)-T_{Air}}{R_{Air}}+C_{Se\mathrm{nsor}}{T}_{\mathrm{Upper}}^{\prime }\left(t\right)\right)& \left(3\right)\end{array}$

[0021] In Equations 2 and 3 above, T.sub.Skin (t) indicates the differential of T.sub.Skin (t) and T.sub.upper (t) indicates the differential of T.sub.upper (t).

[0022] In Equations 2 and 3 above, with C.sub.Body>>C.sub.sensor, Equation 4 below is obtained.

[00002]$\begin{array}{cc}\left[\mathrm{Math}.2\right]& \\ T_{\mathrm{Skin}}\left(t\right)=\left(T_{Skin}\left(0\right)-\frac{T_{Core}\left(R_{Air}+R_{Sensor}\right)+T_{Air}{R}_{\mathrm{Body}}}{R_{\mathrm{Body}}+R_{Air}+R_{Sensor}}\right)\exp \left(\frac{t}{-\frac{R_{\mathrm{Body}}{C}_{\mathrm{Body}}}{1+\frac{R_{\mathrm{Body}}}{R_{Air}+R_{Sensor}}}}\right)+\frac{T_{\mathrm{Core}}\left(R_{Air}+R_{Sensor}\right)+T_{Air}{R}_{\mathrm{Body}}}{R_{\mathrm{Body}}+R_{\mathrm{Air}}+R_{Sensor}}& \left(4\right)\end{array}$

[0023] In Equation 4 above, T.sub.skin(o) denotes the skin surface temperature immediately after the sensor attachment. When curve fitting is used to determine the time constant τ of the changes T.sub.skin(t) in the skin surface temperature over time that best fits the curve of the changes T.sub.skin(t) in the skin surface temperature over time expressed by Equation 4 above, Equation 5 below is obtained.

[00003]$\begin{array}{cc}\left[\mathrm{Math}.3\right]& \\ \tau =\frac{R_{\mathrm{Body}}{C}_{\mathrm{Body}}}{1+\frac{R_{\mathrm{Body}}}{R_{Air}+R_{Sensor}}}& \left(5\right)\end{array}$

[0024] The value of the thermal resistance R.sub.Air of the outside air is a constant value under natural convection and the value does not change. The value of the thermal resistance R.sub.sensor of the sensor 1 is peculiar to the sensor 1 and the value does not change. The value of the ratio of the thermal resistance R.sub.Body and the heat capacity C.sub.Body of the living body 10 is peculiar to the tissue of the living body 10. Consequently, the heat capacity C.sub.Body can be expressed by the equation below by using the thermal resistance R.sub.Body.

C.sub.Body=αR.sub.Body  (6)

[0025] In Equation 6 above, a denotes a coefficient. From the above, the thermal resistance R.sub.Body of the living body 10 is proportional to the square root of the time constant τ.

[0026] Consequently, as for the body 10 whose deep body temperature T.sub.core is to be measured, when the relationship between the time constant τ of the changes T.sub.skin(t) in the skin surface temperature over time immediately after the sensor attachment and the thermal resistance R.sub.Body of the living body 10 is determined by an experiment, a calibration curve L can be obtained as illustrated in FIG. 3, and the thermal resistance R.sub.Body for each time constant τ can be obtained from the calibration curve L. In order to obtain the experimental value (300 in FIG. 3) of the thermal resistance R.sub.Body plotted in FIG. 3, when the deep body temperature T.sub.core at a part around the sensor 1 after the calculation of the time constant τ is measured by, for example, a heat flow compensation method or an eardrum thermometer and at the same time, the skin surface temperature T.sub.skin and the skin surface heat flux H.sub.skin are measured by the sensor 1, the thermal resistance R.sub.Body corresponding to the time constant τ can be obtained by Equation 1.

[0027] FIG. 4 is a flowchart for explaining operations of the temperature measuring device of the present embodiment. The storage unit 2 of the temperature measuring device stores in advance the calibration table in which the thermal resistance R.sub.Body of the living body 10 corresponding to the time constant τ is registered for each time constant τ.

[0028] The time constant calculation unit 3 of the temperature measuring device calculates the time constant τ of the changes T.sub.skin(t) of the skin surface temperature over time immediately after the sensor attachment on the basis of the result of the continuous measurement (step S100 in FIG. 4) of the skin surface temperature T.sub.skin by the sensor 1 (step S101 in FIG. 4). When the skin surface of the living body 10 is covered with the sensor 1, heat is less dissipated from the skin in the covered portion, so the skin surface temperature T.sub.skin rises as compared to a portion exposed to the outside air and then reaches a steady-state value. The time constant calculation unit 3 sets, as the time constant τ, the time until the skin surface temperature T.sub.skin reaches 63.2% of the steady-state value from the rising time point of the skin surface temperature T.sub.skin.

[0029] The thermal resistance derivation unit 4 of the temperature measuring device derives the thermal resistance R.sub.Body by acquiring, from the calibration table of the storage unit 2, the value of the thermal resistance R.sub.Body of the living body 10 corresponding to the time constant τ calculated by the time constant calculation unit 3 (step S102 in FIG. 4).

[0030] Next, the temperature calculation unit 5 of the temperature measuring device calculates the deep body temperature T.sub.Core of the living body 10 by Equation 1 on the basis of the of result of the measurement (step S103 in FIG. 4) of the skin surface temperature T.sub.skin and the skin surface heat flux H.sub.skin in a steady state after the calculation of the time constant τ and the thermal resistance R.sub.Body derived by the thermal resistance derivation unit 4 (FIG. 4 step S104).

[0031] The calculation result output unit 6 of the temperature measuring device outputs the calculation result of the temperature calculation unit 5 (step S105 in FIG. 4). Examples of the output method include the display of the calculation result, the transmission of the calculation result to the outside.

[0032] As described above, in the present embodiment, it is not necessary to input an initial value of the deep body temperature T.sub.core because it is possible to derive the thermal resistance R.sub.Body of the living body 10 only from the calibration table generated in advance, which makes it possible to reduce the burden on a person (a person wearing the sensor 1 or a measurer other than the person) who measures the body temperature T.sub.core.

[0033] The storage unit 2, the time constant calculation unit 3, the thermal resistance derivation unit 4, the temperature calculation unit 5, and the calculation result output unit 6 described in the present embodiment can be implemented by a computer including a central processing unit (CPU), a storage device, and an interface, and a program that controls these hardware resources. An example of the configuration of the computer is illustrated in FIG. 5.

[0034] The computer includes a CPU 200, a storage device 201, and an interface device (hereinafter abbreviated as an I/F) 202. The I/F 202 is for connecting sensor 1, a display device, a communication device, or the like. In such a computer, a program for implementing the temperature measuring method according to embodiments of the present invention is stored in the storage device 201. The CPU 200 executes the processing described in the present embodiment in accordance with the program stored in the storage device 201.

INDUSTRIAL APPLICABILITY

[0035] The embodiments of the present invention can be applied to a technology for measuring the internal temperature of a subject such as a living subject.

REFERENCE SIGNS LIST

[0036] 1 Sensor [0037] 2 Storage unit [0038] 3 Time constant calculation unit [0039] 4 Thermal resistance derivation unit [0040] 5 Temperature calculation unit [0041] 6 Calculation result output unit [0042] 10 Living body [0043] 100 Thermal insulation member [0044] 101, 102 Temperature sensor