Postural control in a simulated saturation dive to 240 msw.

Abstract

INTRODUCTION: There is evidence that increased ambient pressure causes an increase in postural sway. This article documents postural sway at pressures not previously studied and discusses possible mechanisms. METHODS: Eight subjects participated in a dry chamber dive to 240 msw (2.5 MPa) saturation pressure. Two subjects were excluded due to unilateral caloric weakness before the dive. Postural sway was measured on a force platform. The path length described by the center of pressure while standing quietly for 60 seconds was used as test variable. Tests were repeated 38 times in four conditions: with eyes open or closed, while standing on bare platform or on a foam rubber mat. RESULTS: Upon reaching 240 msw, one subject reported vertigo, disequilibrium and nausea, and in all subjects, mean postural sway increased 26% on bare platform with eyes open (p < 0.05) compared to predive values. There was no significant improvement in postural sway during the bottom phase, but a trend was seen toward improvement when the subjects were standing with eyes closed on foam rubber (p = 0.1). Postural sway returned to predive values during the decompression phase. DISCUSSION: Postural imbalance during deep diving has been explained previously as HPNS possibly including a specific effect on the vestibulo-ocular reflex. Although vertigo and imbalance are known to be related to compression rate, this study shows that there remains a measurable increase in postural sway throughout the bottom phase at 240 msw, which seems to be related to absolute pressure.