Local vasomotor responses to rubefacients and ultra‐violet radiation

The increase in blood flow produced by radiant heating of proximal areas of the forearm has been found to be associated with concurrent vasodilatation in the distal portion of the limb (Crockford & Hellon, 1959). This phenomenon is not dependent on central-nervous-system connexions since it occurs in subjects with complete brachial-plexus tears as well as in individuals with nerve blocks between the heated area and the spinal cord (Crockford, Hellon & Parkhouse, 1962). The centrifugal spread of the vasodilatation is prevented, however, by subcutaneous injection of either adrenaline or lignocaine immediately distal to the heated area. It was suggested on the basis of these studies that the spread of the vaso-dilatation may be conducted directly through the muscle walls of the subcutaneous arterial plexus. The present work attempts to determine whether the cutaneous erythema caused by rubefacients or by ultra-violet radiation is associated with changes in blood flow in the forearm similar to those produced by heating. METHODS