Arterial pressure-blood flow relations during limb elevation in man.

The effect of local arterial hypotension upon blood flow was studied in 13 healthy humans. Blood flow was measured by the local 133Xe washout technique in the calf or foot region. Changes in arterial pressure was achieved by elevation of the leg above heart level, while the subject rested in supine position. In papaverine-infiltrated subcutaneous tissue, local arterial pressure and blood flow was linearly related. In subcutaneous and skeletal muscle tissue with normal vasomotor tone, blood flow remained constant during a decrease in regional arterial pressure of 30 mmHg--autoregulation of blood flow. Blood flow ceased in vasoparalysed tissue as well as in tissue with normal vasomotor tone, when the local diastolic arterial pressure was reduced to zero. The elevated foot showed signs of vascular ischaemia during these conditions. When the vessels in the ischaemic foot were distended by inflating a femur cuff to a pressure level above the diastolic blood pressure beneath the cuff, the colour of the foot changed into bluish-red and a substantial blood flow was recorded. It is concluded, that the arteries-arterioles seemed to be collapsed with blood flow cessation, when the diastolic portion of a pulsatile inflow pressure was reduced to zero. Vascular distension seemed to reopen the arterial-arteriolar collapse, and during these conditions the vascular bed offered only little resistance to the systolic peak injection.