Design And Implementation Of Micro System For Skin Blood Flow Detection

Skin blood flow measurement is of great significance to skin microcirculation function evaluation and blood perfusion monitoring.At present,the main method for measuring skin blood flow is based on Doppler principle,but this method is sensitive to human movement and easy to produce artifacts.In addition,because of the large volume of laser Doppler flowmetry,it is difficult to achieve portable measurement.In this thesis,a micro system for skin blood flow detection is designed,which is easy to operate,and the measurement results are not influenced by body movement.The system consists of an array of micro-heaters to heat the skin,measure the temperature of the skin after a few seconds,and calculate the thermal conductivity coefficient of the skin according to the thermal conductivity model of the biological tissues.Then the skin was heated by a central heater,and changes in skin temperature caused by changes in skin blood flow were measured.Skin blood flow was estimated using an approach based on wavelet transform.The hardware design of the system mainly includes:choosing a low-power chip,STM32F103RDT6,as the main control chip,designing a multi-channel constant current source circuit,a heating circuit,a temperature acquisition circuit,a signal processing circuit,a display circuit,and a serial port communication circuit.The software design is based on the Keil V5,including heating control,data acquisition,display and serial port communication programs.Skin blood flow estimation algorithm consists of two procedure.First,the skin thermal conductivity was calculated by solving the semi-infinite unsteady thermal conductivity analysis model in MATLAB.Then,continuous wavelet transform was applied to temperature signals corresponding to changes in skin blood flow.Next,the amplitudes and phases of wavelet coefficients were compensated.Finally,the estimation of skin blood flow was obtained by inverse wavelet transform.To validate the above algorithm,laser Doppler flowmetry was used to simultaneously measure skin blood flow and skin temperature.The temperature signals were analyzed and the results were compared with the skin blood flow signals.The results indicated the feasibility of the algorithm.Moreover,the designed system and laser Doppler flowmetry were used to simultaneously measure skin blood flow on the forearm.The results showed that the signal measured by the designed system had the same trend as that of the signal measured by laser Doppler flowmetry.