Ultrasound assessment of popliteal vein compliance during a short deflation protocol

The purpose of the present study was to determine whether ultrasound is a useful tool to measure the venous characteristics of the lower extremity during a standard venous collecting cuff deflation protocol. To accomplish this, lower extremity pressure-cross-sectional area (CSA) and pressure-volume relationships were measured in eight (25 ± 1 yr) supine subjects. Popliteal vein CSA was assessed by using high-resolution ultrasound, while calf volume changes were simultaneously assessed by using venous occlusion plethysmography (VOP). Pressure-CSA and pressure-volume relationships were assessed at baseline, during the cold pressor (CP) test, and following sublingual nitroglycerin (NTG) administration. Relationships were modeled with a quadratic regression equation, and β1 and β2 were used as indexes of venous compliance. Popliteal vein regression parameters β1 (8.485 ± 2.616 vs. 7.638 ± 2.664, baseline vs. CP; 8.485 ± 2.616 vs. 7.734 ± 3.076, baseline vs. NTG; both P > 0.05) and β2 (−0.0841 ± 0.0241 vs. −0.0793 ± 0.0242, baseline vs. CP; −0.0841 ± 0.0241 vs. −0.0771 ± 0.0280, baseline vs. NTG; both P > 0.05) were not affected by CP or NTG. Similarly, calf regression parameters β1 and β2, obtained with VOP, were not altered during either trial. Intraclass correlations for venous compliance assessed with ultrasound and VOP were 0.92 and 0.97, respectively, indicating acceptable reproducibility. These data suggest that ultrasound is a functional and reproducible tool to assess the venous characteristics of the lower extremity, in addition to VOP. Additionally, popliteal vein and calf compliance were not affected by the CP test or NTG.