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

Content Provider	Semantic Scholar
Copyright Year	2016
Abstract	Published articles and figures have been reprinted with the permission from respective copyright holders. Abstract 7 Abstract Although vasovagal syncope (VVS) is a common clinical condition the mechanisms behind VVS remain elusive. Upright posture is the major trigger of VVS and lower limb blood pooling affecting cardiac output has been proposed as a major determinant. The overall aim of this thesis was twofold. First, to develop new methodology for calculating limb venous compliance. Second, to study lower limb venous volume load and cardiovascular responses during hypovolemic circulatory stress caused by lower body negative pressure (LBNP) in healthy women and women with VVS, emphasizing compensatory mechanisms to maintain central blood volume. Net fluid filtration was associated with an underestimation of venous compliance. This could be accounted for with a correction model. Further, a new venous wall model made it possible to adopt the venous pressure-volume curve through the entire pressure range and thus provide a valid characterization of venous compliance. Calf blood pooling was similar between the groups and was not associated with tolerance to hypovolemic circulatory stress. Venous compliance was reduced at low venous pressures in VVS and correlated with decreased tolerance to circulatory stress. VVS women displayed attenuated sympathetic vasoconstrictor responses during graded circulatory stress, and mobilization of arm capacitance blood as well as capillary fluid absorption from extra-to intravascular space were reduced. Accordingly, more pronounced reductions in cardiac output were found in VVS. Thus, reduced compensatory mechanisms to maintain cardiac output could contribute to the pathogenesis of orthostatic VVS. In healthy women, rapid pooling in the lower limb was associated with higher tolerance to circulatory stress and more efficient cardiovascular responses, in part due to speed-dependent baroreflex-mediated sympathetic activation. In VVS however, rapid lower limb blood pooling was associated with lower tolerance and deficient cardiovascular responses. No speed-dependent baroreflex-mediated sympathetic activation was found in VVS, indicating well-defined differences in cardiovascular regulation already in the initial responses to orthostatic stress. Abstract 8 Populärvetenskaplig sammanfattning 12 List of papers 13 List of papers This thesis is based on the following papers, which are referred to in the text by their Roman numbers. Ewerman L, Lanne T. Calf venous compliance measured by venous occlusion plethysmography: Methodological aspects. Reduced venous compliance – an important determinant for orthostatic intolerance in women with vasovagal syncope. Reduced compensatory responses to maintain central blood volume during hypovolemic stress in women with vasovagal syncope. Submitted. lower limb …
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Language	English
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Subject Keyword	Baroreflex Blood Circulation Blood Volume CNS disorder Cardiac Output Cardiovascular system Copyright Electric Capacitance Entity Handling - upright Ephrin Type-B Receptor 1, human Lower Body Negative Pressure Lower Extremity Paper Plethysmography Poor posture Scientific Publication Shy-Drager Syndrome Structure of calf of leg Syncope (medicine) Trichomonas vaginalis:PrThr:Pt:Cvx:Ord:Wet preparation Vasoconstrictor Agents Vasovagal syncope Venoocclusive disease Venous Blood Pressure filtration holder
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