Validation of the novel venous drainage index with stepwise increases in thigh compression pressure in the quantification of venous obstruction.

BACKGROUND

Venous drainage from the leg is poorly understood, and it is difficult to quantify it hemodynamically. Attempts have been made using duplex ultrasound scanning and venous occlusion air plethysmography (APG). However, they have limited value in day-to-day clinical practice. This is because venous drainage measurements have never been validated successfully against increasing obstruction pressures. The hypothesis is that the novel gravitational venous drainage index (VDI) in milliliters/second is reduced in response to increasing venous obstruction, and the aim was to quantify this, using stepwise inflations of a thigh cuff.

METHODS

Venous drainage tracings were obtained with APG using a dependency to elevation maneuver on the right legs of 21 volunteers (9 female) without venous disease. The test was performed once without a thigh cuff and then with a contoured thigh cuff (18 cm wide) inflated in steps at 10, 20, 30, 40, and 50 mm Hg just before elevation. The function of the thigh cuff was to mimic venous obstruction. The drainage volumes were obtained once the tracing from the elevated cuffed leg decreased to a steady line, when arterial inflow equals venous outflow. The VDI was calculated in the same way as the opposite maneuver, the venous filling index, is obtained from the venous filling tracing (elevation to dependency maneuver), namely, VDI = 90% venous drainage volume/venous drainage time to 90%. The drainage reserve volume (DRV) was defined as the undrained volume caused by the venous obstruction from the thigh cuff.

RESULTS

With stepwise inflations of the thigh cuff at 0, 20, 30, 40, and 50 mm Hg, the median VDI is reduced (26.1, 24.1, 12.1, 7.8, 5.4) and the DRV is increased (0, 5.3, 15.4, 45.5, 62.6). Furthermore, the VDI reductions and the DRV increases correlated significantly (P < .0005) with increasing obstruction pressure at r = -0.69 and r = 0.793, respectively (Spearman).

CONCLUSIONS

The VDI is a novel APG parameter derived from a dependency to elevation maneuver that represents the gravitational venous drainage rate of the leg. The DRV is the undrained venous volume caused by the obstruction from an inflated thigh cuff. Both parameters have been demonstrated to respond to and to correlate with increasing venous obstruction pressures. Their potential clinical value in assessing the hemodynamic significance of an iliac or femoral stenosis and in the screening and selection of patients requiring iliac stenting and follow-up requires further investigation.