title: 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.
authors.affiliation: Department of Medical and Health Sciences, Linköping University, Linköping, Sweden; johan.skoog@liu.se.
authors.forename: Johan
authors.initials: J
authors.lastname: Skoog
authors.affiliation: Department of Medical and Health Sciences, Linköping University, Linköping, Sweden; Department of Cardiology, Linköping University, Linköping, Sweden;
authors.forename: Marcus
authors.initials: M
authors.lastname: Lindenberger
authors.affiliation: Ekman Biomedical Data, Göteborg, Sweden;
authors.forename: Mikael
authors.initials: M
authors.lastname: Ekman
authors.affiliation: Department of Medical and Health Sciences, Linköping University, Linköping, Sweden; Department of Clinical Physiology, Linköping University, Linköping, Sweden; and.
authors.forename: Bengt
authors.initials: B
authors.lastname: Holmberg
authors.affiliation: Department of Medical and Health Sciences, Linköping University, Linköping, Sweden; Department of Clinical Physiology, Linköping University, Linköping, Sweden; and.
authors.forename: Helene
authors.initials: H
authors.lastname: Zachrisson
authors.affiliation: Department of Medical and Health Sciences, Linköping University, Linköping, Sweden; Department of Thoracic and Vascular Surgery, Linköping University, Linköping, Sweden.
authors.forename: Toste
authors.initials: T
authors.lastname: Länne
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D016022:Case-Control Studies; D003187:Compliance; D005260:Female; D006439:Hemodynamics; D006801:Humans; D007866:Leg / Q000098:blood supply*; D008150:Lower Body Negative Pressure; D008955:Models, Cardiovascular; D054971:Orthostatic Intolerance / Q000175:diagnosis / Q000503:physiopathology*; D010991:Plethysmography; D012039:Regional Blood Flow; D019462:Syncope, Vasovagal / Q000175:diagnosis / Q000503:physiopathology*; D014680:Veins / Q000503:physiopathology*; D014690:Venous Pressure; D055815:Young Adult
keywords: orthostatic intolerance; vasovagal syncope; venous capacitance; venous compliance