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OBJECTIVES: This study sought to evaluate postural sway in control subjects with good and poor orthostatic tolerance(OT). BACKGROUND: Some asymptomatic volunteers, when subjected to a progressive orthostatic stress test, show early presyncope. We hypothesized that normal subjects with poor OT do not usually faint because they adopt a strategy of increased lower limb movement, which helps maintain venous return. METHODS: In 12 asymptomatic subjects with good OT and 11 with poor OT, assessed by the combined orthostatic stress of head-up tilting and lower body suction, we determined postural sway using a force platform after 1, 5, and 10 min of motionless standing. RESULTS: The subjects with poor tolerance had greater distances and velocities of sway in the anteroposterior direction but not the mediolateral direction. There was a significant negative correlation between postural sway and orthostatic tolerance. CONCLUSIONS: We have shown that in n ormal subjects with poor OT during a passive orthostatic stress test, their leg movements tend to be greater when standing. These movements are likely to enhanc e venous return and may at least partly explain why, despite their poor test res ults, they do not normally faint.
OBJECTIVES: This study sought to evaluate postural sway in control subjects with good and poor orthostatic tolerance (OT). BACKGROUND: Some asymptomatic volunteers, when subjected to a progressive orthostatic stress test, show early presyncope. We hypothesized that normal subjects with poor OT do not usually faint because they adopt a strategy of increased lower limb movement, which helps maintain venous return. METHODS: In 12 asymptomatic subjects with good OT and 11 with poor OT, assessed by the combined orthostatic stress of head-up tilting and lower body suction , we determined postural sway using a force platform after 1, 5, and 10 min of motionless standing. RESULTS: The subjects with poor tolerance had greater distances and velocities of sway in the anteroposterior direction but not the mediolateral direction. correlation between postural sway and orthostatic tolerance. CONCLUSIONS: We have shown that in n ormal subjects with poor OT during a passi ve legostatic stress test, their leg movements tend to be greater than when standing. These movements are likely to enhanc e venous return and may at least partly explain why, despite their poor test res ults, they do not normally faint.