Acute microcirculatory changes after scalding of the rat paw

A scalding model in the anaesthetized rat was used to measure acute circulatory reactions after heat exposure. Local blood flow of both hindpaws was recorded simultaneously and continuously by laser Doppler flowmetry before, during and for 2 hours following scalding. The scalding injury was inflicted by dipping the right hindpaw into hot water at 60 degrees C for 20 s. Concomitantly, the mean arterial blood pressure (MAP) was displayed on a chart recorder. MAP was obtained by cannulation of the common carotid artery. Oedema formation was calculated by measuring the volume changes of the hindpaws in a plethysmometer before and 30, 60 and 120 min after scalding. Scalding was followed by a biphasic increase of cutaneous circulation. During the first minute after heat provocation, an immediate increase in blood perfusion of about 400% was recorded, followed by a slow decrease of circulation. At 30 min after scalding, there was a secondary phase of increased microcirculation of approximately 230%. A slow decline of cutaneous circulation then followed, and after about 60 min the value was stabilized at approximately 100% above pre-burn level throughout the observation time. Almost no change of perfusion was observed on the contralateral unscalded paw. The scalding injury was followed by a progressive oedema formation on the scalded paw, measured by a volume increase of approximately 72% during the observation period, whereas the non-scalded paw showed no change. MAP remained at a stable level throughout the experiment except for a short-lasting transient increase of approximately 10% at the same time as the first peak of blood perfusion. We could thus confirm that scalding in the present model is accompanied by an immediate and marked increase in the peripheral circulation of the scalded paw followed by a later propagation of oedema, and that these inflammatory changes do not appear to be related to central haemodynamic alterations.