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

Abstract

The influence of lower limb venous compliance on orthostatic vasovagal syncope (VVS) is uncertain. The most widespread technique to calculate venous compliance uses a nonphysiological quadratic regression equation. Our aim was therefore to construct a physiologically derived venous wall model (VWM) for calculation of calf venous compliance and to determine the effect of venous compliance on tolerance to maximal lower body negative pressure (LBNP). Venous occlusion plethysmography was used to study calf volume changes in 15 women with VVS (25.5 ± 1.3 yr of age) and 15 controls (22.8 ± 0.8 yr of age). The fit of the VWM and the regression equation to the experimentally induced pressure-volume curve was examined. Venous compliance was calculated as the derivative of the modeled pressure-volume relationship. Graded LBNP to presyncope was used to determine the LBNP tolerance index (LTI). The VWM displayed a better fit to the experimentally induced pressure-volume curve (P < 0.0001). Calf blood pooling was similar in the groups and was not correlated to the LTI (r = 0.204, P = 0.30). Venous compliance was significantly reduced at low venous pressures in women with VVS (P = 0.042) and correlated to the LTI (r = 0.459, P = 0.014) in the low pressure range. No correlation was found between venous compliance at high venous pressures and the LTI. In conclusion, the new VWM accurately adopted the curvilinear pressure-volume curve, providing a valid characterization of venous compliance. Reduced venous compliance at low venous pressures may adversely affect mobilization of peripheral venous blood to the central circulation during hypovolemic circulatory stress in women with VVS.

Slower Lower Limb Blood Pooling Increases Orthostatic Tolerance in Women with Vasovagal Syncope

“…A total of 29 women participated in the study. Some data on these women have been published earlier (Skoog et al, 2015 , 2016 ). Fourteen women (25.7 ± 1.3 years) had previously been screened at Linköping University Hospital for recurrent episodes of unexplained syncope and diagnosed with VVS by means of a typical, positive head-up-tilt (HUT), and otherwise negative screening.…”

Venous Compliance in Great Saphenous Vein Incompetence: Pre- and Post-interventional Changes

“…8,9 The reason for this is unclear; however, venous compliance was calculated with a new venous wall model able to adopt the curvilinear form of the venous pressureevolume curve and thus characterise compliance correctly over the entire pressure range. 10 A validated correction model was used to subtract the effect of fluid filtration on venous compliance to avoid its confounding effect. 11 This seems especially important as microcirculatory abnormalities have been associated with venous incompetence.…”

“…The calf venous capacitance response (mL/100 mL) was separated from net fluid filtration (mL/100 mL/min) in accordance with previously used techniques. 10,15 Calf venous compliance (mL/100 mL/ mmHg) was calculated as the derivative of the pressuree volume curve during the deflation phase for pressures between 10 and 60 mmHg as described, 10 and a correction model was used to subtract the confounding effect of net fluid filtration on venous compliance. 11 A schematic illustration of the method is shown in Fig.…”

“…The reason for these discrepancies is not clear, although it is possible that methodological difficulties concerning SGP measurements could explain the conflicting results to some extent. 10,11 However, to overcome the inherent problems with previous methods a new venous wall model for calculating venous compliance has been constructed. 10,11 Further, a SGP protocol with standardised superficial venous occlusion was recently developed for evaluation of global venous reflux and pre-operative prediction of radiofrequency ablation (RFA) outcome.…”

“…10,11 However, to overcome the inherent problems with previous methods a new venous wall model for calculating venous compliance has been constructed. 10,11 Further, a SGP protocol with standardised superficial venous occlusion was recently developed for evaluation of global venous reflux and pre-operative prediction of radiofrequency ablation (RFA) outcome. 12 The aim of the study was to add global measurement of calf venous compliance to the SGP protocol.…”