Phase inversion of skin temperature oscillations under the influence of local heating.

The relationship between skin blood flow (SkBF) and skin temperature oscillations (STO) under local heating allows microvascular function and regulation to be assessed. The dynamics of STO during local heating are determined by both SkBF and the diverse mechanisms of heat transfer within biological tissues. The aim of this study is to investigate the changes in the phase and amplitude of STO resulting from local heating. The skin temperature was measured on the palm surface of the distal phalanges of the left hand fingers (index IF, middle MF and ring RF). The research involved a group of 10 healthy participants. Before heating, the STO amplitudes for IF, MF, and RF have almost equal values and oscillations are highly correlated. During heating, the IF amplitude decreases in the intermediate stage but recovers eventually. The IF signal has also undergone phase inversion such that the correlation with other fingers becomes negative. Meanwhile MF-RF correlation remains high throughout the measurement. A mathematical model founded on the heat transfer equation, wherein SkBF oscillations are represented by time-dependent perfusion, reveals that the amplitude and phase of STO are determined by the mean tissue temperature. The relationship between the STO amplitude and phase and tissue temperature during local heating is shaped by both microvascular vasodilation and the thermal boundary conditions. This study introduces a novel approach by combining phase and amplitude analysis of STO and highlights the intricate interplay between microvascular function and thermal dynamics, offering potential advancements in the design of diagnostic tools for assessing vascular health.