Effects of sympathetic activation and nitroglycerin on venous emptying assessed by ultrasound and venous occlusion plethysmography

Assessment of conduit vein function may provide insight into the cardiovascular response to orthostasis. Therefore, the purpose of the current study was to determine if ultrasound is a useful tool to measure the venous characteristics of the lower extremity compared to the previously validated venous occlusion plethysmography (VOP) technique. Lower extremity pressure‐diameter (P‐D) and pressure‐volume (P‐V) relationships were measured in 6 (24 ± 2 yr) supine subjects by using a standard deflation protocol. Popliteal vein diameter was assessed using high resolution ultrasound while calf volume changes were simultaneously assessed using VOP. P‐D and P‐V relationships were assessed at baseline, during the cold pressor test (CP), and following sublingual nitroglycerin (NTG). Relationships were modeled with a quadratic regression equation and β1 and β2 were used as indices of venous compliance. Baseline β1 and β2 were 0.012 ± 0.040; −0.0001 ± 0.0004 and 0.121 ± 0.029; −0.001 ± 0.0003 for ultrasound and VOP, respectively. Popliteal vein and calf compliance were highly correlated at baseline (r=0.91, r 2 =0.83, p < 0.05). A significant correlation was also found between popliteal vein and calf compliance during the CP and NTG trials (CP: r=0.85, r 2 =0.72, p<0.05; NTG: r =0.91, r 2 =0.83, p < 0.05). CP and NTG had no effect on politeal vein or calf compliance parameters, β1 or β2, using either methodology. Preliminary data suggest that ultrasound is a functional tool to assess the venous characteristics of the lower extremity. Additionally, whole limb and single vein compliance were not affected by the CP test or NTG.