Dose-responses of guinea pigs to diazepam at recompression depths

Dose-responses to diazepam were studied in guinea pigs at the recompression pressures used for the treatment of gas embolism and decompression sickness. The conditions and the doses were randomly assigned. Sufficient exposure to 6 ATA air, 3 ATA oxygen, or 1 ATA air was allowed in the hyperbaric chamber before diazepam was administered intravenously. Loss of righting reflex and its return were the end points for sleep and awakening, respectively. The data were analyzed with a mathematical model for dose-response and duration of effect. Results were: (1) in 1 ATA air, widely varying doses induced sleep of long duration; (2) in 6 ATA air, sleep was induced with small doses; and (3) in 3 ATA oxygen, sleep was induced with large doses. The duration of sleep under hyperbaric conditions was shorter than at sea level pressure. The null hypothesis, which assumed similar dose-responses and durations of sleep under these three conditions, was rejected. The dose and duration of diazepam's effect during recompression apparently depend on the pressure and the gas composition used.