Limb venous compliance responses to lower body negative pressure in humans with high blood pressure

Abstract

This study tested the hypothesis that limb venous responses to baroreceptor unloading are altered in individuals with high blood pressure (HBP) compared with normotensive (NT) controls. Calf venous compliance was assessed in 20 subjects with prehypertension and stage-1 hypertension (mean arterial pressure, MAP: 104 ± 1 mm Hg) and 13 NT controls (MAP: 86 ± 2 mm Hg) at baseline and during lower body negative pressure (LBNP), using venous occlusion plethysmography. Baroreflex sensitivity (BRS) was measured using the sequence technique and total peripheral resistance (TPR) was estimated from finger plethysmography. Baseline venous compliance was not different between groups, but the HBP group had lower baseline lnBRS (2.22±0.14 vs 2.7±0.18 ms mm Hg À1) and greater baseline TPR (3828 ± 138 vs 3250 ± 111 dyn sec À1 cm À5 m 2 , Po0.05). Calf venous compliance was reduced in response to LBNP only in the NT group (Po0.05). The HBP group had a greater increase in TPR (DTPR) compared with the NT group ( þ 1649 ± 335 vs þ 718 ± 196 dyn sec À1 cm À5 m 2 , Po0.05). In conclusion, the early stages of hypertension are characterized by an attenuated venoconstrictor response to baroreceptor unloading, which may compensate for an exaggerated vasoconstrictor response and protect against further increases in blood pressure.

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.…”

“…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.…”

“…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).…”