Measurment System Design And Experimental Study On The Thermo-physical Parameters Of Blood Vessel

Biological heat transfer is an important branch of Biomedical Engineering.Measurement of bio-material thermal properties plays an important role in correctunderstanding of the physiological and pathological phenomena, and buildingbio-heat transfer model. In the electrosurgical vessel sealing, thermal from thedevice spread along the blood vessel to the nearby tissues. With the additionalapplication time, the amount of energy will be delivered to the tissue, thetemperature of the nearby tissue will increase. If it is not controlled, the elevatedtemperature in the surrounding tissue can cause irreversible damage to not only thetissue, but can also effect nearby nerves. However, so far there has been littleresearch on the thermo-physical parameters of the blood vessel. It is not enough tosupport the development of the device of blood vessel sealing and controlling thevessel sealing surgical conditions, so it is very necessary for the study of thevascular thermo-physical parameters.This paper first introduces the basic concepts of the steady-state heat transfer.Under the second boundary condition, and solve the steady-state heat conductionmodel of plate and spherical shell using the thermal resistance. On the basis, theplate method and the single probe method was selected to measure thethermo-physical parameters of vascular. The experiment data processing methodwas improved. Plate method can be used to measure thermal parameters of bulktissue, while the probe of measurement of local tissue. During the processing ofexperiment, the steady-state temperature of the tissue should be mesured. Themeasurement system which made by microcontroller and micro-thermistor was usedto realize the function of temperature measurement. Microcontroller willtransmitted the signal to the PC through the serial communication. The program ofthe data processing was prepared to handle the data and display the results.In order to make the measurement system has a high accuracy, some standardsignal was used to calibrate the designed system. After the calibration of thermistorresistance-temperature equation added to the PC program, the system can be used tomeasure the temperature. The measured curve of the system was calibrated by usingthe materials of know thermal parameters. Uncertainty of the measurementtechnique was found to be3.75%when tested in media of known thermal properties.The thermal conductivity and thermal diffusivity of swine aortic in vitro wasmeasured using this technique. The measured conductivity value of the platemethod is0.415W/mk, the probe is0.495W/mK. And the diffusivity is4.628×10-7m2/s and5.517×10-7m2/s. The difference between the two methods maybe caused by the differences water content of the tissues and the experimentalconditions. The thermal conductivity of the blood vessels were measured atdifferent temperatures. It was found that thermal conductivity of the blood vesselwill slightly increase with the temperature rise. The thermal conductivity willreduce obviously when the water content decline.