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The reasons why some apparently healthy people experience sudden and unpredictable fainting attacks remain unclear, although predisposing factors include small blood or plasma volumes, less efficient reflex vasoconstriction and less effective cerebrovascular autoregulation.1 Recently we studied some asymptomatic volunteers who, despite never fainting, had poor tolerance to an orthostatic stress test.2 These subjects had greater postural sway during normal standing than those with good orthostatic tolerance (OT). We suggested that the subjects with poor measured OT who did not normally faint compensated for their poor reflex responses by greater postural sway. This would cause enhanced muscle pumping, thereby reducing venous pooling and preventing fainting during normal standing but not during the orthostatic stress test.
In this study we measured postural sway in patients with posturally related syncope (PRS) who had poor measured OT but without discernable cardiovascular or neurological abnormality. We compared their results with those previously published in two groups of volunteers: with good and with poor OT. Our hypothesis was that postural sway in patients with PRS, unlike non-fainting controls with poor OT, would not be greater than that of the controls with good measured OT and that this could explain their fainting tendency.
Thirteen consecutive patients (aged 35 (4.7) years; six men) were studied who had PRS diagnosed on the basis of their clinical histories (two PRS episodes …