Forefoot vasoconstrictor response to increased venous pressure in normal subjects and in arteriosclerotic patients.

The local vasoconstrictor response to increased venous transmural pressure was studied in the forefoot in 18 normal subjects and in 43 patients with occlusive arterial disease of the lower limbs. Subcutaneous blood flow was measured by the local 133-Xenon wash-out technique. Blood flow measured 40 cm below heart level was compared to blood flow measured at heart level. In 18 normal limbs the vasoconstrictor response caused a decrease in blood flow to a median value of 73%, compared to a median value of 88% in 22 limbs with intermittent claudication without rest pain (p = 0.01). In limbs with ischemic symptoms at rest blood flow increased to a median value of 1.36, when the leg was lowered. Assuming that arterial and venous transmural pressures increase equally during lowering, corresponding to the hydrostatic pressure, keeping the perfusion pressure constant, then the changes in blood flow are due to changes in local peripheral resistance. The significantly smaller decrease in blood flow in claudicants is thus interpreted being due to a functional or structural adaptation of the arterioles to the chronic hypotension. The increase in blood flow during lowering in limbs with rest pain implies a diminished peripheral resistance caused by passive dilation of the arterioles by the increased transmural pressure.