Foot blood flow measurements improve venous plethysmographic studies

The time for foot volume restoration after exercise is widely used as a measure of venous regurgitation. Since this is also a function of arterial inflow rate, we have tested the hypothesis that uncorrected for arterial inflow, these tests may be misleading. Change in venous foot volume after elevation and on exercise was measured in 44 subjects. Arterial inflow was also determined. In a few patients arterial flow was varied by cooling or by exercise. The times of half-volume restoration were measured. Calculated were: the rate of total blood flow into the foot; the rate of venous regurgitation; and "venous sufficiency indices" for elevation and for exercise with and without correction for arterial inflow rate. These indices combine volume and time data in a single numeric value. Volume change on elevation was uninfluenced by the rate of arterial inflow. Volume change on exercise and the halftime of volume restoration varied significantly with the rate of arterial inflow as did the "venous sufficiency indices." These variances were significantly reduced by correcting for arterial inflow rate. We conclude that for foot volume studies to measure regurgitation and for data obtained at different times to be comparable, corrections must be made for the rate of arterial inflow to the foot.