Patterns of blood flow in the microcirculation of the skin during the course of the tuberculin reaction in normal human subjects.

Digital thermographic imaging and laser-Doppler velocimetry techniques were used to study the sequence of microcirculatory changes in typical Type IV (DHS-type) skin reactions to intradermal injection of PPD into seven healthy tuberculin-positive subjects. Thermography has shown that there is very little change in thermal status at 6 hr, that there is an area of raised temperature roughly corresponding to that of erythema around the site of antigen injection at 24 hr, and that the area of 'hot' skin starts to exceed that of the clinically observed reaction at 48 hr and remains extensive even at 96 hr. The area of the increased RBC flux detected by the laser-Doppler technique corresponded generally to that of erythema for the first 48 hr, but thereafter became smaller than the clinically observable reaction. Cuff occlusion experiments showed that the phenomenon of reactive hyperaemia is abolished at 24 and 48 hr in conditions of maximal hyperaemia, but that this response is recovering by 96 hr. Vasomotion was significantly exaggerated between 48 hr and 96 hr. These studies indicate that there is maximal arteriolar vasodilatation during the first 2 days of the reaction with rapid blood flow in the congested capillaries of the dermal papillae, and that engorgement of deeper venous plexus of the dermis is the predominant vascular change in the resolving response at 72-96 hr.