VISUAL-VESTIBULAR EFFECTS OF INERT-GAS NARCOSIS

Divers breathing compressed air at depths beyond 30 m experience a typ e of behavioural impairment known as inert gas narcosis. This conditio n degrades performance on a wide range of tasks and has the potential to compromise safety. Symptoms associated with narcosis include slowed response time, amnesia, and euphoria. Studies have also found disturb ances to mechanisms regulating ocular control in response to vestibula r stimulation; however, these experiments have been limited to very lo w frequency head movement (0.2 Hz). Thus, to further examine the effec ts of narcosis on visual/vestibular mechanisms, the vestibular ocular reflex (VOR) was assessed across a range of higher frequencies more re presentative of natural head movement (2.0-4.7 Hz). Seven subjects wer e tested prior to, during and after exposure to narcosis which was ind uced using 30% nitrous oxide. Standard room air was breathed as a cont rol. The results indicated that narcosis decreased the velocity of com pensatory eye movements in response to head rotation (decrease in VOR- gain), with more pronounced decreases occurring at the higher frequenc ies. The lag between eye and head position (phase lag) was also decrea sed by nitrous oxide; an effect that was again more pronounced at high er frequencies. These results indicate that narcosis disrupts ocular r egulatory mechanisms which help to stabilize images on the retina duri ng head movement.