Autoregulation in the human forearm: differences between normal subjects and patients with hypertension

Autoregulation was assessed in the forearm vascular bed of 16 men with normal arterial pressure and 19 patients with hypertension. The perfusion pressure was varied by changing the height of the forearm above the heart and blood flow was measured by venous occlusion plethysmography. In normal subjects, autoregulation was weak and flow usually increased more than pressure. In the hypertensive patients autoregulation was, on average, better than in the normal subjects, but the responses varied widely; in some patients, blood flow fell as pressure increased. The pattern of responses observed in the patients could be the result of a functional change in the smooth muscle, but it could also be the result of an increased wall: lumen ratio in the resistance vessels.