Adrenergic mechanisms do not contribute to age-related decreases in calf venous compliance

Abstract

Limb venous compliance decreases with advancing age, even in healthy humans. To test the hypothesis that adrenergic mechanisms contribute to age-associated reductions in limb venous compliance, we measured calf venous compliance before and during acute systemic α- and β-adrenergic blockade in eight young (27 ± 1 yr old, mean ± SE) and eight older healthy men (67 ± 2 yr old). Calf venous compliance was determined in supine subjects by inflating a thigh-collecting cuff to 60 mmHg for 8 min and then decreasing it (1 mmHg/s) to 0 mmHg while calf volume was indexed with a strain gauge. The slope (·10⁻³) of the pressure-compliance relation (compliance= β₁ + 2·β₂·cuff pressure), which is the first derivative of the quadratic pressure-volume relation [(Δlimb volume) = β₀+ β₁·(cuff pressure) + β₂·(cuff pressure)²] during reductions in cuff pressure, was used to quantify calf venous compliance. Calf venous compliance was ∼30% lower (P < 0.01) in older compared with young men before adrenergic blockade. In response to adrenergic blockade calf venous compliance did not increase in young (-2.62 ± 0.14 and -2.29 ± 0.18 ml·dl⁻¹·mmHg⁻¹, before and during blockade, respectively) or older men (-1.78 ± 0.27 and -1.68 ± 0.21 ml·dl⁻¹ ·mmHg⁻¹). Moreover, during adrenergic blockade differences in calf venous compliance between young and older men observed before adrenergic blockade persisted. Collectively, these data strongly suggest that adrenergic mechanisms neither directly restrain calf venous compliance in young or older men nor do they contribute to age-associated reductions in calf venous compliance in healthy men.

Cardiovascular regulation in women with vasovagal syncope : With special reference to the venous system

“…Present assessments commonly use a mathematically derived quadratic regression equation (QRE) to model the venous pressure-volume curve and the first derivative of this equation to characterize venous compliance. With this approach, venous compliance is bound to become negative at a pressure within or very close to the applied physiological pressure range, precluding a valid interpretation (86)(87)(88)90,92,93). In accordance, we found that 10% of the subjects at 55 mmHg and almost 75% of the subjects at 60 mmHg displayed a negative Ccalf with the QRE.…”

“…Other factors, such as physical activity and sympathetic tone, could influence the measurements of Ccalf (87,132). However, there were no differences in physical activity between the groups and although activation of the sympathetic system has been shown to lower unstressed venous volume, increased sympathetic activation does not appear to directly affect venous compliance (90,93).…”

“…The major shortcoming is that the curvilinear pressure-volume relation is fitted to a strict mathematical parabolic function. With this approach, venous compliance is bound to become negative at a pressure within or very close to the applied physiological pressure range, precluding a valid interpretation (86)(87)(88)90,92,93). Due to the form of the venous pressure-volume curve it appears to be of great importance to model the whole curve accurately, especially since gravitational forces could increase venous pressure well above 60 mmHg during prolonged standing.…”

“…However, the QRE is a strict mathematical function and with this approach venous compliance is bound to become negative at a pressure within or very close to the applied physiological pressure range, precluding a valid interpretation of compliance at high venous pressures (86)(87)(88)90,92,93). Therefore, we developed a new venous wall model (VWM), for characterization of the venous pressure-volume curve and compliance (see Results).…”

Reduced venous compliance: an important determinant for orthostatic intolerance in women with vasovagal syncope

“…Present assessments commonly use a mathematically derived quadratic regression equation (QRE) to model the venous pressure-volume curve and the first derivative of this equation to characterize venous compliance. With this approach, venous compliance is bound to become negative at a pressure within or very close to the applied physiological pressure range, precluding a valid interpretation (13,17,(32)(33)(34)43).Venous compliance has not been accurately measured in a well-defined VVS population, although lower limb venous pooling may be of pathophysiological importance. The aim of the present study was, therefore, 1) to introduce and validate a new physiologically derived three-parameter venous wall model (VWM) for the characterization of the venous pressure-volume relationship and 2) to accurately study calf venous compliance (C calf ), as well as the calf venous capacitance (V cap ) response (blood pooling), and assess its impact on orthostatic tolerance to lower body negative pressure (LBNP) in women diagnosed with VVS and matched controls.…”