DYNAMIC THERMOGRAPHIC IMAGING FOR ESTIMATION OF REGIONAL PERFUSION INTHE TUBERCULIN REACTION IN HEALTHY-ADULTS

A sensitive method for measurement of the volume of blood flow through the skin, based on the kinetics of reheating after localised cooling, is described in this paper. This method has been used to study the tu berculin reaction as a model of cutaneous delayed-type hypersensitivit y (DHS) in man. Over the positive reaction there is accelerated reheat ing similar in kinetics and extent to that seen after maximal hyperaem ia induced by intradermal injection of histamine or prostaglandin E2. The earlier phase of reheating (10-100 s) is more dependent on blood f low, whereas the later phase (100-300 s) is apparently more dependent on non-perfusion heat exchange mechanisms, including conduction. The r eheat kinetic method is largely dependent on blood flow in the deep de rmal vessels (diameter > 50 mum), whereas the alternative approach of measurement of the velocity of flow of erythrocytes in the microcircul ation by laser Doppler (LD) flowmetry gives results biased towards the most superficial dermal circulation. Previous studies with LD flowmet ry have shown that the blood velocity is greatest at the centre of wea k and strong reactions, while in the most intense reactions it is rais ed at the centre but maximal at the periphery (central relative slowin g, CRS) raising the possibility of central ischaemia. The reheat kinet ics approach has now indicated that the deep dermal circulation is not impaired in CRS reactions. It is concluded that there must be partial obstruction of the parts of the microcirculation communicating betwee n the deep and superficial dermal plexuses, presumably from the accumu lation of exudate oedema in the most intense tuberculin reactions.