The effect on skin blood flow of short-term venous hypertension in normal subjects. Plugging of skin capillaries by activated white blood cells is one of the proposed mechanisms by which skin damage may be initiated in chronic venous insufficiency. The aim of this study was to determine whether a microcirculatory deficit was induced in the skin by raising the venous pressure proximally for thirty minutes. Seventeen subjects with no evidence of venous or arterial disease had laser Doppler velocimetry performed in the goiter region of the leg; 8 different subjects had the measurement done on the dorsum of the hand. Peak hyperemic response following three minutes of ischemia was measured before and after a thirty-minute period of sustained venous hypertension applied by a proximal tourniquet inflated to 80 mm Hg. A decrease in the peak flow: baseline flow ratio (median ratio 2.25 before, 1.70 after, p less than 0.02) and an increase in the time taken to reach maximal hyperemia (median time ten seconds before, twenty seconds after, p less than 0.01) were observed after the period of venous hypertension in the lower limb. The second parameter, but not the first, was significantly affected in the upper limb. The authors conclude that a microvascular deficit in the skin is demonstrable after a short period of venous hypertension. This is consistent with the white-cell-trapping theory, but other possible explanations are discussed. 