A Zero-Heat-Flow Transducer for Monitoring Perfusion Blood Temperature

The transducer in which the zero-heat-flow method was applied is designed for monitoring the blood temperature flowing in a tube. The circumference of the probe was heated or cooled to the same temperature as the tube-surface temperature which finally showed the blood temperature, so that the net heat flow across the probe was reduced to zero. Experiments showed that the water temperature could be measured from the surface of a vinyl-chloride tube with the accuracy of ±0.2°C between 20 and 400°C of water temperature. The measured temperature was not affected by the ambient temperature, tube thickness, tube material, and flow rate. Time delay of ramp-like change in the water temperature was around 2 min to measure on the vinyl-chloride tube. Time delay depends on the heat capacity of the metal frame, the thermal conductivity of the tube material, and the power of thermomodule. The in vivo experiment of this device appeared to be satisfactry with a high accuracy and good response time.