Venous outflow and inflow resistance in health and venous disease

The purpose of this study was to develop a physiologic method to measure outflow and inflow from the lower extremities and thus to quantify the degree of venous valvular insufficiency and venous obstructive disease.

Calibrated photoplethysmography was used in combination with passive changes in hydrostatic pressure, by leg elevation followed by repositioning of the leg to the original sitting position. With the principle of venous occlusion plethysmography, timed volume changes were then used to calculate the outflow and inflow. The inflow and outflow units were the percentage of optical reflectance (%OR) per minute. The respective resistances were calculated by identifying the hydrostatic pressure distance from the third intercostal space to the probe site that is inducing these site changes. The resistance units were millimeters of Mercury x minutes per %OR.

Four groups of subjects were examined: normal individuals, patients with venous valvular insufficiency, deep venous thrombosis, and a combination of both. The most significant differences in outflow values were found between the control group (81.77% OR/min) and the deep venous thrombosis group (28.47% OR/min). In contrast, the most significant differences in inflow values were found between the control group (9. 67% OR/min) and the venous valvular insufficiency group (108.61% OR/min). The resistances changed correspondingly.

The application of calibrated photoplethysmography in conjunction with induced changes in leg hydrostatic pressure proved to be an effective physiologic method to noninvasively quantify venous hemodynamics in normal control subjects, patients with venous valvular insufficiency, venous obstructive disease, or both.