Lower panel: Subject's arm, with a blood pressure cuff around the bicep, is supported so that the mid forearm is slightly above heart level. Upper panel: Pressure cycles in the blood pressure cuff. During the time of elevated pressure, venous outflow is prevented, but arterial inflow is unimpeded. Consequently the limb swells as the arterial inflow accumulates. The rate of inflow is determined from the slope of the accompanying record of forearm circumference, obtained from a gauge around the mid forearm.