Mechanism Study Of Thermal Methods For The Detection Of Diabetic Microvascular Dysfunction

Microvascular diseases are one of the initiators of diabetes and related chronic complica-tions.They often occur in the early stage and run through the process of diabetes,and have influences on the health of large vessels and other organs.Therefore,the detection of micro-vascular diseases is of extreme importance for the early diagnosis of diabetes and related com-plications.Aiming at studying the mechanism of thermal methods for the detection of diabetic microvascular dysfunction,the dissertation focuses on the issues of fluid-structure interaction and heat and mass transfer related to the mechanism,where the theoretical,numerical and ex-perimental researches were carried out.The main contents are described as follows:1.Model analysis of the influence of diabetic microvascular dysfunction on body thermoreg-ulation.A multi-scale model of human thermoregulation was developed and adopted to simulate thermoregulation disorders under heat stress caused by exercise.Simulated results showed that both skin and core temperatures were raised up faster than those of healthy persons caused by lower maximum sweat production and sweat production rate.On the other hand,when the function of vasodilation was injured,core temperature was also raised up faster as the result of the decrease of skin blood flow,however,the skin temperature was raised up more slowly than that of healthy persons.2.Model analysis of endothelial regulation and oscillation mechanism of small artery.Endo-thelium-dependent vasodilation model of small artery was developed,which can be de-scribed as the interaction process among the concentrations of NO,Ca2+,phosphorylated myosin and the variation of artery radius.The model was adopted to simulate the regulating process of small artery for the changes of blood flow rate.Simulated results showed that in the process of autoregulation,the dynamic reaction of active substances and vasomotion transformed from an initial state to a new equilibrium state with periodic damped oscilla-tions of the concentrations of NO in vascular wall and the vascular diameter.It is proved by stability analysis of system that this oscillation during the dynamic regulating process is caused by the feedback control of wall shear stress.3.Model analysis of the influence of microvascular dysfunction on skin temperature oscilla-tion.A coupling flow and heat transfer model was built by considering the interplay be-tween capillary network and interstitial tissue using immersed boundary method,and was adopted to simulate the influence of blood flow oscillations on skin temperature.Amplitude attenuation and phase delay of temperature fluctuations as they propagate in tissue were also analyzed.It is indicated that skin temperature oscillation in lower frequency ranges can be detected with less amplitude attenuation and phase delay.When the perfusions of some network branches are lost,the temperature oscillation becomes weaker.4.Experimental validations of thermal methods for the detection of diabetic skin microvas-cular dysfunctions:Skin LDF(laser doppler flowmetry)and temperature signals were ob-tained by experiments and analyzed based on wavelet transformation.Firstly,periodic pul-sation features of human skin LDF signals were verified;then,the skin LDF and tempera-ture signals were proved to be correlated closely in low frequency ranges.After that,ther-mal sensitivities in different body regions were compared and it was found that human toe was a sensitive area for the detection of diabetic microvascular dysfunctions.Additionally,Experiments on rats showed that their LDF signals also presented periodic pulsation fea-tures,but the characteristic frequencies of regulation activities were about 4-6 times as those of human.Under the stimulus of local heating and reactive hyperemia,the variations of rats' skin temperature oscillations in the diabetic group statistically differed from the control group,which indicated that microvascular dysfunctions occurred.Finally,the soft-ware which can perform wavelet analysis of LDF and temperature signals and give quan-tified indices for evaluation of local regulatory activities of microcirculation was developed based on MATLAB.