Hyperventilation effect on postural sway

Objective: To examine the effect of voluntary hyperventilation (HV) on postural sway. Design: Crossover controlled, experimental study. Setting: Human movement and balance clinical research unit. Subjects: Four different groups of normal subjects ( n = 6, 6, 7, and 9) and patients with bilateral absence of vestibular function ( n = 9). Intervention: Partial carbon dioxide pressure (tc-P co 2) was measured transcutaneously with surface electrodes. Body sway was measured with a force platform immediately after maximal voluntary HV for 30 to 90 seconds. Recordings were obtained with eyes open and eyes closed, standing on the platform and on foam-rubber, and after head or body movements. Main Outcome Measure: Postural sway. Results: HV increased body sway in all conditions, but the effects were more intense when subjects were standing directly on the platform surface with their eyes closed. Recordings after HV of 30, 60, and 90sec in normal subjects showed that although CO 2 levels were inversely related to the duration of HV, body sway did not increase further. HV also increased sway after active movements by the subjects. The main sway increase was in sway area and mean and maximal deviations but less for mean sway velocity. HV preferentially increased low-frequency sway oscillations. These effects were also present in labyrinthine-defective subjects. Conclusions: HV increases body sway, but the relationship between CO 2 levels and degree of unsteadiness is not linear. The dizziness reported by patients with HV syndrome may be partly caused by objective unsteadiness. The presence of HV-induced unsteadiness in patients with absent vestibular function indicates that the effects of HV are not mediated by the labyrinth.