Additive effects of obesity and hypertension to limit venous volume

Abstract

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.