A Study of Body Temperature Measurement Using the Zero-Heat-Flow Technique

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The deep body thermometer is an instrument for body temperature monitoring in which zero-heat-flow technique is employed. It was invented by Fox in 1971. improved by one of the investigator of this project (T.T.). and now spreading for post operative patient monitoring and many other applications. However. its ultimate accuracy has not been well studied. The project was planned to investigate the accuracy of the deep body thermometer. and also to provide a modification of the probe design. which is critical to the accuracy.The probe of the deep body thermometer was modified so that a slight positive feedback control was introduced to compensate the error due to a heat flow from the deep tissue to the ambient air detouring the probe. The performance of the probe was examined by 1) numerical analysis. 2) simulator experiment. and 3) measurements in volunteer subjects.As the results. it was shown by the numerical analysis and the simulator experiment that the modification in the probe design significantly reduces the measurement error. The subject study showed that the averaged differences between measured body temperatures by the modified probe and a sublingual thermistor probe remained within 0.1゜C in a room temperature of 20゜C and 25゜C.From these results. it was confirmed that the modification in the probe design could realize accuracy which satisfies most demands of clinical body temperature measurements.