Research On Portable Equipment Of Monitoring Brain Core Temperature Based On Zero-heat-flow Principle

Human core temperature of brain is an important physiological parameter. It plays a major role in the disease monitoring, diagnosis and treatment. Therefore monitoring the human core temperature is of great significance to the early detection, diagnosis and treatment of the diseases. Due to the closeness of the brain and the importance of safety, temperature measurement methods commonly used such as direct contact,infrared temperature measurement are not suitable for continuous detection of core temperature for a long time. To address this issue, based on zero-heat-flow (ZHF)principle we design and implement a core temperature detection device (ZHF sensor)with a low-cost MSP430 microcontroller chip and PT100 temperature sensors. The sensor part uses two sets of PT100 thermistors and a precise reference resistor for constant current source temperature measurement, an amplifier AD620 to amplify the temperature change signal, and an MSP430 12-bit analog-to-digital converter to collect voltage signal. The control module controls the heating module by PI control algorithm through the processing and analyzing the collected data to achieve zero heat flow for core temperature of human brain. Compared with the traditional temperature measurement equipment, it has the following advantages:(1) provides a portable monitoring method of core temperature to make up core temperature research for the domestic;(2) using the zero heat flow method, in the forehead site to collect the brain core temperature, non-invasive monitoring method makes the core temperature detection is easy to be accepted;(3) using constant current source method, the circuit structure is simple, and maintain the thermistor PT100 in a small temperature range (32-42℃) within the linear characteristics, improving the accuracy of temperature measurement;(4) the use of battery-powered, through the portable design concept, relative to the traditional monitoring equipment flexible, making the core temperature detection can be anytime, anywhere;(5) designed with MSP430F149 chip and a common sensor, making the core temperature detection costs greatly reduced;(6) The design of the core temperature acquisition system can obtain the rhythm of human body core temperature.During the experiment, in order to ensure the reliability and accuracy of the experiment, we calibrated the temperature sensor by a constant temperature water bath. To demonstrate the practicality of the device, we captured the brain core temperature of 26 volunteers using an ear thermometer and the ZHF sensor independently. By comparing of experimental results we found that there was no significant difference between the two temperature values by the two methods.Meanwhile we also monitored the core temperature of one volunteer continuously using the ear thermometer and the ZHF sensor for 5 days to observe the circadian rhythm of the core temperature. In this experiment, we found that the temperature range by the ear thermometer was (37.06±0.21)℃, while the temperature range by the ZHF sensor was (37.17 ± 0.24)℃. Through the covariance analysis,correlation coefficient p = 0.92 > 0.8,it was found that the changing trends of the temperature values by the two methods had a high degree of correlation and consistency.