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Limb venous tone and responsiveness in hypertensive humans

¹Department of Health, Nutrition, and Exercise Sciences, University of Delaware, Newark, Delaware; ²Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri; and ³Christiana Care Health Services, Cardiovascular Clinical Trials, Newark, Delaware

Submitted 25 April 2008 ; accepted in final form 12 July 2008

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.

nitroglycerin; cold pressor test; postexercise ischemia; venous smooth muscle tone