METHODS

Seventeen healthy men and one woman, 18-25 years of age, were studied. The studies were done with the subject lying supine in a warm room (26 C)+ The lower body was enclosed in an airtight box to the level of the iliac crests. A polyethylene cannula was inserted into an antecubital vein and advanced into an intrathoracic vein to measure central venous pressure.

Blood Aow to the forearm was measured with a Whitney mercury-in-Silastic strain-gauge plethysmograph compensated for temperature variations (19). The strain gauge was placed around the right forearm 2-3 inches distal to the elbow at a tension of 15 g. The arm was elevated and supported at the wrist so that the proximal part of the forearm was about 10 cm above the anterior chest wall. A pneumatic cuff was placed around the upper arm and inflated intermittently above venous pressure for 7-9 set The rate of increase in volume of the forearm during intermittent venous occlusion is directly proportional to blood flow (Fig. 1). In 13 of the 18 subjects blood flow to a finger was measured on the same side. An air plethysmograph was placed on the middle finger and connected to a Sanborn transducer(model 270) to measure changes in volume during venous occlusion. Pneumatic cuffs were placed around the wrist and the proximal part of the middle finger. These cuffs were inflated simultaneously and at the same pressure as the cuff around the upper arm. The finger cuff allowed measurement of blood flow to the finger during venous occlusion and the wrist cuff prevented return of blood from the hand to the forearm. In the five subjects in whom finger blood flow was not measured, a pneumatic cuff was placed around the wrist and inflated to suprasystolic pressure during the period of measurement to exclude the contribution of hand blood flow from the measurement of forearm flow.