Increased postural sway in control subjects with poor orthostatic tolerance.

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 normal subjects with poor OT during a passive orthostatic stress test, their leg movements tend to be greater when standing. These movements are likely to enhance venous return and may at least partly explain why, despite their poor test results, they do not normally faint.