AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 2 562-R568, Copyright © 1995 by American Physiological Society
Additive effects of obesity and hypertension to limit venous volume
K. Stepniakowski and B. M. Egan
Department of Pharmacology, Medical University of South Carolina, Charleston 29425-2251.
The presence of reduced venous distensibility in obesity might have
important hemodynamic effects and could indirectly implicate a role for
metabolic factors in vascular control, because loading conditions are
different in arterial and in venous vessels. Forearm blood flow and venous
volume were measured plethysmographically in 58 subjects, including lean
and obese hypertensives and normotensives. Venous volume at 30 mmHg (VV30)
was decreased by both obesity and hypertension. This coincided with
evidence for better preservation of central blood and stroke volumes with
upright posture in obese than in lean subjects. Furthermore, obese
hypertensives had lower VV30 than either lean hypertensives or obese
normotensives. Postischemic forearm vascular resistance, a surrogate marker
for structural luminal cross-sectional area, percent body fat, and fasting
insulin each correlated independently with VV30 (P < 0.05) in
multivariate analysis. Because nonesterified fatty acid levels are elevated
in obese hypertensives and may have potent vascular effects, dorsal hand
vein responses to coinfusion of Intralipid 10% and heparin to raise fatty
acids locally were obtained in normal volunteers. The local infusion of
Intralipid with heparin reduced hand vein distensibility, whereas dextrose
and heparin did not (11 +/- 3% vs. 0 +/- 2%, respectively, P < 0.01).
This study indicates that obesity and mild hypertension each reduce venous
distensibility and that the coexistence of both conditions produces an even
greater impairment in venous capacitance. The reduced venous distensibility
in obesity appears to reflect structural as well as functional factors and
to have systemic hemodynamic effects.
