Vascular resistance in peripheral blood vessels at normotension and at local orthostatic hypertension in healty humans.
The effect of changes in orthostatic pressure on vascular resistance in subcutaneous adipose tissue was examined in the forearm at normal tension and in the leg at local orthostatic hypertension in three normal subjects. Blood flow in subcutaneous tissue was measured by the local xenon-133 washout technique. Changes in orthostatic pressure were achieved by postural changes of the extremity. At levels above the heart where venous pressure is constant, there was autoregulation of blood flow over a wider arterial blood pressure range in leg than in forearm. When transmural pressure increased 25 mm Hg or more vascular resistance increased about 50 per cent in the dependent forearm and 300 per cent in the dependent leg. The effect of ischemia on vascular resistance was investigated in cutaneous tissue of hand and foot by means of the 131I-Antipyrine initial slope technique. Vascular resistance after maximum dilatation achieved after 20, 30, and 35 min of ischemia was less in vessels of the hand than in vessels of the foot. Thus, adaptive structural changes of vessels subjected to increased blood pressure are present in cutaneous and subcutaneous adipose tissues in normal subjects.