Patent Publication Number: US-2023145806-A1

Title: Temperature Measurement Device and Temperature Measurement Method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase entry of PCT Application No. PCT/JP2020/018095, filed on Apr. 28, 2020, which application is hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a temperature measuring device and a temperature measuring method that measure the internal temperature of a subject such as a living body. 
     BACKGROUND 
     In a substance, for example, a living body, when a certain depth is exceeded from the epidermis toward a deep body, there is a temperature area that is not affected by changes in outside air temperature, or the like, and the temperature of this area is called a deep body temperature or a core body temperature. On the other hand, the temperature of a surface layer of a living body that is susceptible to changes in outside air temperature is called a body surface temperature. The body surface temperature may be measured by a percutaneous thermometer in the related art. The body temperature measured by such a percutaneous thermometer in the related art may not reflect the deep body temperature. Therefore, it is difficult to directly measure the deep body temperature, which is the temperature in the deep area of the living body, like the body surface temperature. 
     Therefore, the inventor proposed a noninvasive deep body temperature measurement technology for measuring a skin surface heat flux H Skin  and a skin surface temperature T Skin  by a sensor installed on a skin surface and estimating a deep body temperature T core  by using these measured values and biothermal resistance R Body  given by initial calibration (see NPL 1 and NPL 2). An equation for estimating the deep body temperature T core  is as follows. 
         T   core   =T   Skin   +R   Body   H   skin   (1)
 
     However, the technology disclosed in NPL 1 and NPL 2 requires the biothermal resistance R Body  to be derived by inputting an initial value of the deep body temperature T core  at the time of initial calibration before the start of measurement, so the burden on a person who measures the deep body temperature T core  is heavy. 
     CITATION LIST 
     Non Patent Literature 
     
         
         NPL 1: Daichi Matsunaga, Yujiro Tanaka, Tomoko Seyama, “Study for miniaturization of a noninvasive deep body temperature sensor considering convection change”, 2020 Institute of Electronics, Information and Communication Engineers (IEICE) General Conference, Communication lecture Proceedings 1, B-19-9, 2020 
         NPL 2: Daichi Matsunaga, Yujiro Tanaka, Tomoko Seyama, “Study of a noninvasive deep body temperature estimation method for convection change in outside air”, 2019 Institute of Electronics, Information and Communication Engineers (IEICE) Communication Society Conference, Communication lecture Proceedings 1, B-19-15, 2019 
       
    
     SUMMARY 
     Technical Problem 
     The present invention has been made to solve the above problems, and an object of the present invention is to provide a temperature measuring device and a temperature measuring method, capable of reducing the burden on a person who measures the internal temperature of a subject such as a living subject. 
     Means for Solving the Problem 
     A temperature measuring device according to embodiments of the present invention includes: a sensor configured to measure a temperature of a surface of a subject and a heat flux on the surface; a time constant calculation unit configured to calculate a time constant of changes in the temperature over time on the basis of a measurement result of the temperature; a thermal resistance derivation unit configured to derive thermal resistance of the subject on the basis of the time constant; and a temperature calculation unit configured to calculate an internal temperature of the subject on the basis of the temperature, the heat flux, and the thermal resistance. 
     Furthermore, a temperature measuring method according to embodiments of the present invention includes: a first step of measuring a temperature of a surface of a subject; a second step of calculating a time constant of changes in the temperature over time on the basis of a measurement result of the temperature; a third step of deriving thermal resistance of the subject on the basis of the time constant; a fourth step of measuring the temperature of the surface of the subject and a heat flux on the surface; and a fifth step of calculating an internal temperature of the subject on the basis of a measurement result in the fourth step and the thermal resistance calculated in the third step. 
     Effects of the Invention 
     According to embodiments of the present invention, providing a time constant calculation unit and a thermal resistance derivation unit enables to derive the thermal resistance of a subject at the start of measurement, so that it is not necessary to input the initial value of the internal temperature of the subject and it is possible to reduce the burden on a person who measures the internal temperature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram illustrating the configuration of a temperature measuring device according to an embodiment of the present invention. 
         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. 
         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. 
         FIG.  4    is a flowchart for explaining operations of the temperature measuring device according to the embodiment of the present invention. 
         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 
     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 skin  of a skin surface of a living body  10  (subject) and a heat flux H skin  on the skin surface, a storage unit  2  that stores in advance a calibration table in which thermal resistance R Body  of the living body  10  corresponding to a time constant τ of changes in the temperature T skin  over time is registered, a time constant calculation unit  3  that calculates the time constant τ of the changes in the temperature T skin  over time on the basis of the measurement result of the temperature T skin , a thermal resistance derivation unit  4  that derives the thermal resistance R 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 core  (internal temperature) of the living body  10  on the basis of the temperature T skin , the heat flux H skin , and the thermal resistance R Body , and a calculation result output unit  6  that outputs the calculation result of the deep body temperature T core . 
     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 skin  of the skin surface of the living body  10 . Furthermore, it is possible to derive the heat flux H skin  of the skin surface on the basis of a difference between the temperature T skin  of the skin surface and a temperature T 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   . 
       FIG.  2    is a diagram illustrating a thermal equivalent circuit model of the sensor  1  and the living body  10 . In  FIG.  2   , T 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 Air  denotes an outside air temperature, R Body  denotes the thermal resistance of the living body  10 , R sensor  is the thermal resistance of the sensor  1 , R Air  denotes the heat resistance of outside air, C Body  denotes the heat capacity of the living body  10 , and C sensor  denotes the heat capacity of the sensor  1 . 
     The changes T skin (t) in the temperature of the skin surface of the living body  10  over time immediately after sensor attachment and the changes T 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 Air , the deep body temperature T Core  of the living body  10 , the thermal resistance R Body  of the living body  10 , the thermal resistance R sensor  of the sensor  1 , the thermal resistance R Air  of the outside air, the heat capacity C Body  of the living body  10 , and the heat capacity C sensor  of the sensor  1 . 
     
       
         
           
             
               
                 
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     The value of the thermal resistance R 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 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 Body  and the heat capacity C Body  of the living body  10  is peculiar to the tissue of the living body  10 . Consequently, the heat capacity C Body  can be expressed by the equation below by using the thermal resistance R Body . 
         C   Body   =αR   Body   (6)
 
     In Equation 6 above, a denotes a coefficient. From the above, the thermal resistance R Body  of the living body  10  is proportional to the square root of the time constant τ. 
     Consequently, as for the body  10  whose deep body temperature T core  is to be measured, when the relationship between the time constant τ of the changes T skin (t) in the skin surface temperature over time immediately after the sensor attachment and the thermal resistance R 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 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 Body  plotted in  FIG.  3   , when the deep body temperature T 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 skin  and the skin surface heat flux H skin  are measured by the sensor  1 , the thermal resistance R Body  corresponding to the time constant τ can be obtained by Equation 1. 
       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 Body  of the living body  10  corresponding to the time constant τ is registered for each time constant τ. 
     The time constant calculation unit  3  of the temperature measuring device calculates the time constant τ of the changes T 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 S 100  in  FIG.  4   ) of the skin surface temperature T skin  by the sensor  1  (step S 101  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 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 skin  reaches 63.2% of the steady-state value from the rising time point of the skin surface temperature T skin . 
     The thermal resistance derivation unit  4  of the temperature measuring device derives the thermal resistance R Body  by acquiring, from the calibration table of the storage unit  2 , the value of the thermal resistance R Body  of the living body  10  corresponding to the time constant τ calculated by the time constant calculation unit  3  (step S 102  in  FIG.  4   ). 
     Next, the temperature calculation unit  5  of the temperature measuring device calculates the deep body temperature T Core  of the living body  10  by Equation 1 on the basis of the of result of the measurement (step S 103  in  FIG.  4   ) of the skin surface temperature T skin  and the skin surface heat flux H skin  in a steady state after the calculation of the time constant τ and the thermal resistance R Body  derived by the thermal resistance derivation unit  4  ( FIG.  4    step S 104 ). 
     The calculation result output unit  6  of the temperature measuring device outputs the calculation result of the temperature calculation unit  5  (step S 105  in  FIG.  4   ). Examples of the output method include the display of the calculation result, the transmission of the calculation result to the outside. 
     As described above, in the present embodiment, it is not necessary to input an initial value of the deep body temperature T core  because it is possible to derive the thermal resistance R 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 core . 
     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   . 
     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 
     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 
     
         
           1  Sensor 
           2  Storage unit 
           3  Time constant calculation unit 
           4  Thermal resistance derivation unit 
           5  Temperature calculation unit 
           6  Calculation result output unit 
           10  Living body 
           100  Thermal insulation member 
           101 ,  102  Temperature sensor