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

Abstract

We conducted a series of studies to develop and test a rapid, noninvasive method to measure limb venous compliance in humans. First, we measured forearm volume (mercury-in-Silastic strain gauges) and antecubital intravenous pressure 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 index of intravenous pressure. In subsequent studies, we measured forearm and calf venous compliance by inflating the venous collecting cuff to 60 mmHg for 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 (Δlimb volume) = β0 + β1 ⋅ (cuff pressure) + β2 ⋅ (cuff pressure)2, where Δ is change. Curves generated with this method were reproducible from day to day (coefficient of variation: 4.9%). In 11 subjects we measured venous compliance via this method under two conditions: with and without (in random 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); however, the data suggest that unstressed volume was reduced by the maneuver. These studies demonstrate that venous pressure-volume curves can be generated both rapidly and noninvasively with this technique. Furthermore, the results suggest that although whole-limb venous compliance is under negligible sympathetic control in humans, unstressed volume can be affected by the sympathetic nervous system.