Measurement of limb venous compliance in humans: technical considerations and physiological findings

We conducted a series of studies to develop and test a rapid, noninvasive m ethod to measure limb venous compliance in humans. First, we measured forea rm volume (mercury-in-Silastic strain gauges) and antecubital intravenous p ressure during inflation of a venous collecting cuff around the upper arm. Intravenous pressure fit the regression line, -0.3 +/- 0.7 + 0.95 +/- 0.02. cuff pressure (r = 0.99 +/- 0.00), indicating cuff pressure is a good inde x of intravenous pressure. In subsequent studies, we measured forearm and c alf venous compliance by inflating the venous collecting cuff to 60 mmHg fo r 4 min, then decreasing cuff pressure at 1 mmHg/s (over 1 min) to 0 mmHg, using cuff pressure as an estimate of venous pressure. This method produced pressure-volume curves fitting the quadratic regression (Delta limb volume ) = beta(0) + beta(1)-(cuff pressure) + beta(2) (cuff pressure)(2), where D elta is change. Curves generated with this method were reproducible from da y to day (coefficient of variation: 4.9%). In 11 subjects we measured venou s compliance via this method under two conditions: with and without (in ran dom order) superimposed sympathetic activation (ischemic handgrip exercise to fatigue followed by postexercise ischemia). Calf and forearm compliance did not differ between control and sympathetic activation (P > 0.05); howev er, the data suggest that unstressed volume was reduced by the maneuver. Th ese studies demonstrate that venous pressure-volume curves can be generated both rapidly and noninvasively with this technique. Furthermore, the resul ts suggest that although whole-limb venous compliance is under negligible s ympathetic control in humans, unstressed volume can be affected by the symp athetic nervous system.