Local regulation of cutaneous blood flow in psoriasis.

Local regulation of cutaneous blood flow (CBF), i.e., the venoarteriolar reflex mechanism and the autoregulation response, was studied in 27 patients with psoriasis using atraumatic epicutaneous 133Xe-labeling tracer washout technique. Venous stasis of 40 mm Hg induced a significant reduction in CBF--as in normal subjects (i.e., a vasoconstrictor response)-in both involved psoriatic skin (0.47 +/- SEM 0.04, p less than 0.0001) and uninvolved psoriatic skin (0.38 +/- SEM 0.03, p less than 0.0001). The vasoconstrictor response to neural blockade with lidocaine was investigated in two control experiments in psoriatic skin. It was found to be normal: neural blockade with lidocaine 2 cm outside the measured field did not affect the vasoconstrictor response, whereas local infiltration with lidocaine did block the vasoconstrictor reflex. Limb elevation of 40 cm above heart level induced a 2-fold significant increase in the CBF of involved psoriatic skin in 10 patients. This response is a paradoxical deviation from normal local autoregulation of the CBF (p less than 0.002). Limb elevation had no significant influence on CBF of uninvolved psoriatic skin, indicating a normal autoregulation of the CBF. The paradoxical increase in CBF during limb elevation in involved psoriatic skin was not influenced by local neural blockade with lidocaine, or by local neural and vascular, smooth muscle blockade obtained by injection of lidocaine and papaverine. The results indicate that the reason for this paradoxical phenomenon might be due to the special morphology of the capillaries of involved psoriatic skin.