Reduced venous compliance - an important determinant for orthostatic intolerance in XXXX with @entity907 .

@entity432 @entity1 @entity291 @entity907
UNASSIGNED: The influence of lower limb venous compliance on orthostatic @entity907 is uncertain. The most widespread technique to calculate venous compliance uses a non-physiological quadratic regression equation. The aim was therefore to construct a physiologically derived venous wall model for calculation of @entity291 venous compliance, and to determine the effect of venous compliance on tolerance to maximal lower body negative pressure (LBNP). @entity432 plethysmography was used to study @entity291 volume changes in 15 @entity1 with @entity907 (25.5  1.3 yrs.) and 15 controls (22.8  0.8 yrs.). The fit of the venous wall model and the regression equation to the experimentally induced pressure-volume curve were examined. Venous compliance was calculated as the derivative of the modeled pressure-volume relation. Graded LBNP to presyncope was used to determine LBNP tolerance index (LTI). The venous wall model displayed a better fit to the experimentally induced pressure-volume curve (P<0.0001). @entity291 blood pooling was similar in the groups and was uncorrelated to LTI (r=0.204, P=0.30). Venous compliance was significantly reduced at low venous pressures in vasovagal @entity1 (P=0.042), and correlated to LTI (r=0.459, P=0.014) at the low pressure range. No correlation between venous compliance at high venous pressures and LTI was found. In conclusion, the new venous wall model 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 @entity1 with @entity907 .
