Duration of increase in vascular volume during venous stasis

Duration of increase in vascular volume in the crus following application of venous stasis was studied in 3 healthy subjects placed in a supine position. Changes in calf volume during venous stasis was measured by plethysmography. In one series of experiments changes in vascular volume were studied by measurements of accumulation of 133Xenon proximal to a depot located in the anterior tibial muscle. In another series of experiments changes in activity of 99mTc-labelled erythrocytes were used as indicator for changes in vascular volume. Following application of venous stasis in the horizontal position the rate of increase in calf volume declined to a steady level after about 5 min. Both the studies with 133Xenon and with 99mTc-erythrocytes indicate that vascular volume continued to increase for 3, 3.5 and 5 min following venous stasis of 20, 30 and 40 mmHg, respectively. When the crus was lowered 50 cm below heart level the duration of increase in vascular volume following an additional increase in venous pressure induced by venous stasis was shorter than in the horizontal position. When the calf is placed at heart level the results indicate that for up to 5 min after application of venous stasis of 40 mmHg both increase in vascular volume and transcapillary fluid filtration contribute to the observed increase in calf volume. Using the rate of increase in calf volume within 5 min after induction of venous stasis thus leads to overestimation of CFC. After 5 min vascular volume appears to remain constant and the observed increase in calf volume seems to be solely due to a net increase in interstitial fluid volume.