JPH047458B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of the Invention The present invention relates to an electronic thermometer, and particularly to an electronic thermometer that can measure the body temperature of a subject at an early stage after starting measurement.

(b) Prior art and its problems Generally, electronic thermometers using temperature sensors such as mercury thermometers and thermistors are used to measure body temperature. Normally, the detection part of these thermometers is inserted under the armpit or under the tongue when taking measurements, but since it takes time for the detection part to reach a state of thermal equilibrium with the body temperature, there is a problem in that it takes a long time to complete the measurement. be.
Therefore, in order to solve this problem and measure body temperature early, conventional electronic thermometers insert the sensor part into the armpit, etc., and add a certain temperature (for example, 0.5 degrees Celsius) after a certain period of time after starting the measurement. A method was used to predict body temperature. However, the degree of increase in detected temperature during body temperature measurement varies depending on the individual (for example, the time constant for reaching an equilibrium state differs). The above-mentioned conventional electronic thermometer completely ignores such individual variations, and therefore has the disadvantage that the obtained measurement results are low in accuracy. Therefore, in order to solve this drawback, the applicant of this application has decided to calculate the logarithm of the time differential of the body temperature to be measured.
There is a linear relationship between T _L and time t, and T _L = A
Focusing on the fact that the temperature can be expressed as -τ't, constants A and τ' are determined by a regression method, and an application has already been filed for an electronic thermometer in which convergence body temperature is predicted from these constants.

On the other hand, in body temperature measurement, if we consider the process until the equilibrium state value (saturation value is obtained), the rise immediately after the start of measurement is the response characteristic of the temperature sensor that moves from the initial value To to the surface temperature of the measurement site ( (see ○B in Figure 1) is dominant, and then passes through a transitional intermediate region to a region where the response of the organism (see ○C in Figure 1) becomes significant, reaching an equilibrium state. The area where the response is dominant is, for example, under the tongue, where the initial surface temperature To' of the measurement site equilibrates to the deep temperature by closing the mouth and bringing the probe into close contact with the tongue.

As mentioned above, the actual response curve of the thermometer (first
When considering how the temperature (see Figure ○A) changes over time, it is thought that two time constants are dominant. That is, it is necessary to calculate by a logical formula using two time constants. However, if two formulas are used, the calculation becomes very complicated, so conventionally, including the electronic thermometer using the regression method of the earlier application, a logical formula using one time constant has been used to simplify the calculation. It was already undergoing a transformation. Therefore, there was a problem that the accuracy was not sufficient.

(c) Purpose of the Invention In view of the above, the purpose of the present invention is to provide an electronic thermometer that is capable of short-time measurement and is highly accurate.

(d) Structure and Effects of the Invention In order to achieve the above object, the electronic thermometer of the present invention focuses on the fact that the dominant response region of the time constant of the temperature sensor after the start of measurement is relatively short. Data is not taken in using the regression method for a predetermined time after the start of measurement, and the convergence body temperature is predicted and calculated using the regression method after the predetermined time has elapsed.
That is, the electronic thermometer of the present invention includes a sensor for detecting body temperature, a timer for measuring a predetermined time after the start of measurement, a means for storing the output of the sensor as an initial value T _p after the elapse of the predetermined time, and the predetermined sampling the output of the sensor after a period of time;
means for calculating the logarithm value T _Li of the time differential of each detection output at each of the n sampling times ti; Based on the logarithm value of the time differential of the output T _L1 ,...T _Lo , the linear equation T _L = A-1/
Means for calculating the constants A and 1/τ of τ・t by a regression method, and means for predicting and calculating the body temperature Ts after thermal equilibrium based on the calculated constants A and 1/τ and the detected initial temperature T _p It is configured.

According to the electronic thermometer of this invention, a constant that differs for each individual is calculated by a regression method to predict convergence body temperature, so body temperature can be measured quickly and accurately without being influenced by individual variations. I can do it. Furthermore, since the converged body temperature prediction calculation is performed using a regression method after a predetermined period of time after the start of measurement, the body temperature can be measured by considering only the biological time constant without being affected by the time constant of the temperature sensor. Furthermore, it is possible to measure body temperature with higher accuracy using a simple logical formula.

Here, in order to facilitate understanding of the electronic thermometer of the present invention, the principle of its adoption will be explained.

Generally, when time is plotted on the horizontal axis and temperature is plotted on the vertical axis, the passage of time when body temperature is measured by a temperature sensor changes exponentially as shown in FIG. 1.

In Figure 1, the region 0≦t≦ta is the region where the time constant of the temperature sensor is dominant, and this region can be considered to be sufficiently short for predicting the convergence value of body temperature (temperature (It can be shortened by reducing the heat capacity of the sensor.) Therefore, if we discard the data in this region and treat only the data after ta, the region will be dominated only by the biological time constant, so we only need to consider one time constant, and the theoretical formula will become simpler.

In this case, the change in body temperature over time, that is, the temperature T at time t, is expressed by the following equation.

T=Ts−(Ts−To′)e ^t/ 〓 (1) Where, Ts: Convergence value To′: Initial value τ: Biological time constant From the above formula, to find the convergence value Ts, the initial value
To′ is required as a constant. However, since To' is the temperature at the start of measurement at the measurement site and cannot be measured, it is possible to use a fixed value determined in advance from experimental values as the value of To, but it is recommended to ignore individual differences and fix it. will cause an error.

So, considering the equation when the time domain is shifted by t→t-tp and tp, However, Tp: is the actual measured value of T at t=tp. That is, Tp, which can be measured, can be used instead of To'.

Differentiating the above equation (2) with respect to t gives us becomes. Further, by taking the logarithm of both sides of this equation (3), logT'=logTs-Tp/τ-t-tp/τ=tp/τ+logTs-Tp/τ-1/τt (4). Here, if we set T _L = logT', A = tp/τ+logTs-Tp/τ, equation (4) becomes T _L = A-1/τt (5), and T _L is expressed as a linear expression of t. .

Since the temperature T is actually measured at each time t after ta, T'=dT/dt can be determined, and T _L =logT' can also be determined. Therefore
(t1,
For the data pairs of T _L1 ), (t2, T _L2 ), ... (tn, T _Lo ), the constant A,1/τ of the regression line can be calculated using the least squares method. That is, The constant A and 1/τ can be found.

On the other hand, as described above, since logTs-Tp/τ=A-tp/τ, the convergence temperature Ts is Ts=τe _o 〓 ^j=1 +Tp (8). In this equation (8), the initial value To is actually measured, and the constant A and 1/τ are calculated using equations (6) and (7), so the convergence value Ts can be calculated.

(e) Description of Examples The present invention will be explained in more detail below with reference to Examples.

FIG. 2 is a block diagram of an electronic thermometer in which the present invention is implemented. In the figure, 1 is a sensor such as a thermistor for detecting body temperature, 2 is an A/D converter that converts the output from sensor 1 from an analog signal to a digital signal, and 3 is a CPU, which is the A/D converter 2. After receiving the detected temperature signal from the ROM 4, it performs control for predicting the convergence temperature Ts, which will be described later, according to a program stored in the ROM 4. 5 is a RAM that stores various data during the control process. 6 is a display that displays the measured body temperature. This display 6
As the display body, well-known ones such as liquid crystal, light emitting diode, fluorescent display tube, etc. are used. 7 is a switch for instructing the start of measurement.

Next, the operation of the electronic thermometer of the above embodiment will be explained with reference to the flowchart shown in FIG.

When switch 7 is turned on and operation starts,
First, in step ST1, the number of samples n (=n1) is set in the sample counter arranged in the RAM5. This sample circuit n indicates the number of sample times required for one prediction calculation. Next, the process waits in ST2 until the sample time arrives, and when the sample time arrives, the process moves to the next step, ST2. If this sample time is, for example, 1 second, a series of processes in the measurement cycle from ST3 onwards progresses every second. ST3
Here, it is determined whether ti≧10, that is, whether 10 seconds have passed since the thermometer was operated. this
10 seconds corresponds to ta in Fig. 1, and during this time, you do nothing and wait. When 10 seconds have elapsed after the operation, the judgment of ST3 becomes YES, and here the A/D
The detected temperature T1 at that time is taken in through converter 2,
Store time t1 and temperature T1 in RAM 5 (ST4).
Next, calculate the time differential value dT1/dt of the detected temperature T1 (ST5), and further calculate the logarithm value T _L 1 of this time differential value.
Find = logdT1/dt (ST6). Based on the calculated T _L1 and the sample time t1 at that time, _i 〓 T _Li = _i-1 〓 T _Li -1 + T _{Li i} 〓 ti = _i-1 〓 ti-1 + ti _i 〓 ti ² = _i-1 〓 ti ² -1+ti ² _i 〓 t _Li ti= _i-1 〓 T _Li -1ti-1+T _Li ti is calculated and stored in the RAM 5 (ST7). Next, it is determined whether the sample time number i has reached a preset n (ST8), and if it has not reached it (naturally NO if i = 1), the process returns to step ST2, and from now on, the sample time will be sampled. Steps ST3 and ST each time the sample time arrives until the number i reaches n.
4,...Repeat the process of ST7. Through this processing, _o 〓 ⁱ⁼¹ T _Li , _o 〓 ⁱ⁼¹ ti, _o 〓 ⁱ⁼¹ ti ² , _o 〓 ⁱ⁼¹ T _Li ti are stored in the RAM 5.

When the sample time count i reaches n, step
If the judgment in ST8 is YES, then based on the stored data _o 〓 ⁱ⁼¹ T _li , _o 〓 ⁱ⁼¹ ti, _o 〓 ⁱ⁼¹ ti ² , _o 〓 ⁱ⁼¹ T _li ti, the above
The constant A is calculated using the equation (6) (ST9), and the constant 1/τ is further calculated using the above equation (7) (ST10). As a result, the specific curve unique to the person to be measured is specified, and then using the above equation (8),
Calculate the convergence temperature Ts (ST11). Note that as the initial value Tp in equation (8), any value determined between ta≦tp≦tb may be used; however, when tp=tb,
By using the Tp value, that is, the newest measured temperature value in the sampling data, a constant closer to the result can be found, and the predicted value will also be more accurate.

When the calculation of the convergence temperature Ts is completed in ST11, this temperature Ts is displayed as body temperature on the display 6 (ST1
2).

After the display, if the detected temperature is still increasing, the judgment of dTi/dt≦0 in ST13 becomes NO, and then the contents of the sample counter are further changed to +.
n1 (ST14), returns to ST2, and the same process as above is repeated. That is, this time, as shown in FIG. 4, sampling is performed n1 times in the area from tb to tc. However, data such as ΣT _Li , Σti, Σti ² , ΣT _Li ti, etc. used in the calculation of A and 1/τ are obtained by adding data from tb to the data obtained in the area from ta to tb.
Accumulate data in the tc area. In this way, even after the second convergence temperature prediction calculation is completed, if dTi/dti≦0 is still not found, the contents of the sample counter are further incremented by +n1, and then as shown in Figure 4. Then, sampling is performed n1 times in the region from tc to td. Then, the data obtained by sampling in the region from tc to td is accumulated on the data obtained during the previous two predicted value calculations, and based on these accumulated data, constants A and 1/τ are calculated, and the convergence value is calculated.
Predictively calculate Ts.

The change in detected temperature is 0, that is, dTi/dti≦0
This means that the measurement end point has been reached, and other necessary measurement end processing is subsequently performed.

In addition, in the above embodiment, the determination of dTi/dti≦0 is to determine the measurement end point, but instead of this, the determination of the measurement end point is made when dTi/dti becomes below a certain finite value, or This may be performed after a certain period of time has elapsed or a combination of these.

As described above, according to the electronic thermometer of this embodiment, data is started from ta in FIG. 1, the regression line is obtained using the data up to tb, and the convergence value Ts is calculated from the constant. Moreover, it is repeated every predetermined time until the measurement is completed.
It is possible to predict the convergence value of body temperature.

Further, according to the electronic thermometer of this embodiment, the time constant τ can be determined each time a measurement is performed, and individual differences can be constantly corrected, making it possible to make highly accurate predictions. Furthermore, even if the measurement site is different, such as under the tongue or under the armpit, τ is calculated each time, so measurement can be performed without changing any constants.

Furthermore, according to this example electronic thermometer,
Since the data immediately before the start of measurement is discarded and measurements are made in a region that depends only on the time constant of the living body, the theoretical formula can be simplified and highly accurate measurements can be made. In particular, since the constants necessary for prediction use the values actually measured each time a measurement is made, compared to a case where a uniquely fixed constant is given, it is possible to not only correct for individual differences between subjects, but also to adjust for the state at that time. Even the corresponding constant can be provided, and highly accurate predictions can be made from this point of view.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the response characteristics of the thermometer over time, FIG. 2 is a block diagram of an electronic thermometer in which the present invention is implemented, and FIG. 3 is a flow diagram for explaining the operation of the electronic thermometer. FIG. 4 is a diagram for explaining the timing of predictive calculation and the accumulation of sampling data in the operation of the electronic thermometer. 1...Sensor, 2...A/D converter, 3...
CPU, 4...ROM, 5...RAM, 6...Display, 7...Start switch.

Claims (1)

[Claims] 1 a sensor for detecting body temperature; a timer for measuring a predetermined time after the start of measurement; a means for storing the output of the sensor as an initial value T _p after the predetermined time has elapsed; means for sampling the output of the sensor and calculating the logarithm value T _Li of the time differential of each detected output at each of the n sample times ti; and each of the sample times t1, . . .
Constant A and 1/τ of the linear equation T _L =A-1/τt based on tn and the calculated sample time t1,...logarithm T _L1 ,...T _Lo of the time differential of the detection output for each tn.
An electronic thermometer comprising means for calculating by a regression method; and means for predicting and calculating a body temperature Ts after thermal equilibrium based on the calculated constants A and 1/τ and the initial temperature T _p .