Faster Lower Limb Blood Pooling Is Associated with Reduced LBNP‐Tolerance in Women Prone to Vasovagal Syncope

Abstract

Objective We recently presented slower lower limb venous blood pooling in healthy women with reduced orthostatic tolerance. Venous distension rate affects the prevailing sympathetic response, and people prone to syncope seem to have altered cardiovascular response to orthostatic stress. The aim was to study lower limb blood pooling and its effects on tolerance to lower body negative pressure (LBNP) in women prone to vasovagal syncope (VVS). Methods: Graded LBNP to presyncope was used to determine LBNP tolerance index (LTI) in 13 young women with VVS and 15 matched controls. During LBNP the blood pooling rate was evaluated with volumetric technique. Cardiovascular responses were also monitored. Results: Within the control group, a faster rate of blood pooling was associated with increased LTI (P < 0.05), and in addition correlated to a smaller LBNP-induced decline in stroke volume (P < 0.05) and pulse pressure (P < 0.05). In contrast, within the VVS group a faster rate of blood pooling was associated with decreased LTI (P < 0.01), and with a greater decline in stroke volume (P < 0.05). Conclusions In accordance with the previous study, a faster rate of lower limb blood pooling was associated with increased orthostatic tolerance in women with no history of syncope. Interestingly, the opposite pattern was found in women prone to vasovagal syncope, indicating essential differences in blood pressure regulation. One plausible mechanism could be altered baroreceptor function and/or different concomitant sympathetic response during hypovolemic stimulus in women prone to vasovagal syncope.