A harmonic-wave bio-thermal method for continuous monitoring skin thermal conductivity and capillary perfusion rate

The revelation of thermal energy exchange mechanism of human body is challenging yet worthwhile, because it can clearly explain the changes in human symptoms and health status. Understanding, the heat transfer of the skin is significant because the skin is the foremost organ for the energy exchange between the human body and the environment. In order to diagnose the physiological conditions of human skin without causing any damage, it is necessary to use a non-invasive measurement technique by means of a conformal flexible sensor. The harmonic method can minimize the thermal-induced injury to the skin due to its low heat generating properties. A novel type of computational theory assessing skin thermal conductivity, blood perfusion rate of capillaries in the dermis, and superficial subcutaneous tissues was formed by combining the multi-medium thermal diffusion model and the bio-thermal model (Pennes equation). The skins of the hand back of six healthy subjects were measured. It was found that the results revealed no consistent changes in thermal conductivity were observed across genders and ages. The measured blood perfusion rates were within the range of human capillary flow. It was found that female subjects had a higher perfusion rate range (0.0058–0.0061 s−1) than male subjects (0.0032–0.0049 s−1), which is consistent with invasive medical studies about the gender difference in blood flow rates and stimulated effects in relaxation situations.