Observation of skin thermal inertia distribution during reactive hyperaemia using a single-hood measurement system.

An attempt was made to image the thermal inertia (defined as the square root of the product of thermal conductivity, specific heat and density) of the skin to observe the distribution of blood in the skin during post-occlusive reactive hyperaemia in normal healthy volunteers. The method was based on the ability to calculate thermal inertia by successive thermographic measurements of the skin after stepwise change in ambient radiation temperature surrounding the skin area. The stepwise change was achieved within 0.1 s through a single hood. Experimentation on the undisturbed volar forearm of normal subjects at the same site showed that the measurements thus achieved were reproducible. The thermal inertia values of forearm skin in normal subjects were scattered throughout the range 1.1 x 10(3) to 1.7 x 10(3) W s(1/2) m(-2) K(-1). Experiments on forearm skin subjected to arterial cuff occlusion indicated that thermal inertia can be detected at a low level of blood perfusion. A linear relationship was observed between thermal inertia and blood perfusion measured by laser Doppler imager before and during blood flow occlusion. During reactive hyperaemia, the thermal inertia image exhibited a non-uniform island-shaped pattern of distribution over the forearm, suggesting that, after release from occlusion, recovery of blood flow is non-uniform.