Reflex heating of the skin and telethermography.

Thermography is a very instructive method of showing the interaction between direct changes in heat radiation of the surface of the skin and its relation to reflex processes. Short reflex arcs, such as the axon reflex, and long reflex arcs, such as the flush phenomenon provoked by visceral cutaneous reflexes, can be illustrated by thermography. Reflex changes in skin temperature by cooling the skin of patients with cold contact urticaria with the short-term development of large areas of warmed skin and also reflex changes in cholinergic urticaria after prior heating of such skin areas where the urticarial eruption follows are reflected in the picture of telethermography. Reflex arcs between extremities affect the arterial blood flow and show individual variation, as in the case of the cessation of permanent local vasoconstriction by indirect cooling. The thermographic illustration of convective heat transport to the skin surface can be obstructed by the cooling effect of sweat secretion, e.g., water vapor exudation and by changes in conductive heat transport in abnormal skin.