Limb venous tone and responsiveness in hypertensive humans

Abstract

Hypertensive (HTN) animal models demonstrate lower venous compliance as well as increased venous tone and responsiveness compared with normotensive (NTN) controls. However, the extent to which findings in experimental animals can be extended to humans is unknown. Forearm and calf venous compliance were quantified in 9 NTN (23 ± 1 yr) and 9 HTN (24 ± 1 yr) men at baseline, after administration of nitroglycerin (NTG), during a cold pressor test (CP), and post-handgrip exercise ischemia (PEI). Individual pressure-volume relationships from a cuff deflation protocol (1 mmHg/s) were modeled with a quadratic regression. Regression parameters β1 and β2 were used to calculate compliance. A one-way ANOVA was used to compare the beta parameters and a repeated-measures ANOVA was used to compare volumes across all pressures (between groups at baseline and within groups during perturbations). Limb venous compliance was similar between groups (forearm: NTN β1 = 0.11 ± 0.01 and β2 = −0.00097 ± 0.0001, HTN β1 = 0.10 ± 0.01 and β2 = −0.00088 ± 0.0001; calf: NTN β1 = 0.12 ± 0.01 and β2 = −0.00102 ± 0.0001, HTN β1 = 0.11 ± 0.01 and β2 = −0.00090 ± 0.0001). However, at baseline, volume across all pressures (i.e., capacitance) was lower in the forearm ( P ≤ 0.01) and tended to be lower in the calf ( P = 0.08) in HTN subjects. Venous compliance was not altered by any perturbation in either group. Forearm volume was increased during NTG in HTN subjects only. While venous compliance was similar between NTN and HTN adults, HTN adults have lower forearm venous capacitance (volume) which is increased with NTG. These data suggest that young HTN adults may have augmented venous smooth muscle tone compared with NTN controls.