FIGURE 5.

Method of venous occlusion plethysmography. The arm is enclosed in a rigid airtight box, sealed at junction of arm and box. A tourniquet is applied to the arm outside the box, sufficient to prevent blood passing out, but insufficient to prevent blood passing in. The manometer within is calibrated to generate flow from pressure change in the box. Before inflating the tourniquet, pressure is atmospheric and there is no pulsation of pressure. After tourniquet inflation, pressure rises in the box and shows marked pulsations that correspond with the arterial pulse.