Ambulatory venous pressure, air plethysmography, and the role of calf venous pump in chronic venous disease

Abstract

Background: Ambulatory venous pressure (AMVP) records pressure dynamics with calf exercise. Air plethysmography (APG) measures related volume detail. APG has been suggested as a noninvasive surrogate for AMVP. We examine the correlations between APG and AMVP parameters and the role of "calf pump failure" in chronic venous disease (CVD).

Methods: A total of 8456 limbs in 4610 patients investigated for CVD during a 20-year period were analyzed. APG and AMVP data were available in 4599 limbs for calculation of Pearson correlation coefficient; 1347 of these limbs had significant iliac vein stenosis, proven by intravascular ultrasound. Venn diagrams are used to explore overlapping incidence of APG and AMVP abnormalities.

Results: APG calf volume and reflux (venous volume, venous filling index) showed progressively significant deterioration with advancing Clinical, Etiology, Anatomy, and Pathophysiology (CEAP) clinical class, anatomic extent of reflux (superficial, deep, perforator), and reflux severity (axial reflux, segmental score). Notably, calf ejection volume increased in a nearly linear fashion (R = 0.71) to venous volume such that residual volume fraction (RVF) remained normal even in the worst of these categories. AMVP too progressively deteriorated with clinical disease and reflux severity. Venous filling time was the key parameter as the pressure drop alone was abnormal in only 4% of the limbs analyzed. There was no correlation between RVF and AMVP (R = 0.22) or between AMVP and many other APG parameters. Venn distribution showed only minor overlap (30%) between AMVP and key APG abnormalities overall, but the overlap increases from 40% to 70% in advanced clinical and reflux categories. AMVP was rarely abnormal (7%) when APG was normal. Median AMVP was normal in calf pump failure categories, however defined (subnormal ejection fraction, RVF, or both). Median AMVP is normal in venous obstruction without reflux, while AMVP abnormalities are associated three to seven times more with reflux than with obstruction.

Conclusions: APG (venous filling index) is a useful index of reflux. Calf pump ejection is a powerful and plastic compensatory mechanism, and calf pump failure is rare. Ambulatory venous hypertension is dominantly associated with reflux and less with obstruction. AMVP too worsens with clinical and reflux severity categories. However, there is little correlation between APG and AMVP parameters as APG measures volume and AMVP measures pressure, each in its own domain, and the volume-pressure curve is nonlinear. AMVP may be omitted in routine clinical testing if APG is normal, as the yield (7%) will be very low. AMVP reflects venous hypertension, the end stage in CVD. AMVP should be used to identify such cases when APG is abnormal.

Keywords: Air plethysmography; Ambulatory venous pressure; Calf pump failure.