Changes in Sleep Patterns during Simulated Nitrox Saturation Diving to 20 and 30 Meters

This study assessed the effect of a nitrogen-oxygen (N₂-O₂) saturation diving environment on nocturnal sleep and the differences in sleep on diving depth. We measured and recorded the standard polysomnograph and heart rate for a total of 459 nights on 27 divers who performed the N₂-O₂ saturation simulation dive at 20- and 30-m equivalent depths as well as their subjective feelings of fatigue. From the last half of the period on the bottom to the postdive period of both saturation diving depths, our main findings included a prolongation of sleep latency, shortened total sleep time, a decreased sleep efficiency index, and increased feelings of fatigue. During the bottom period and decompression period, the total number of awakenings and the awakenings from rapid eyes movement (REM) sleep increased. This was slightly greater at the 30-m equivalent depth. From these facts, we assumed that the deterioration of sleep at the 20- and 30-m nitrox saturation dives was predominantly relative to being restricted in a closed environment for a long time and the lack of physical activity of the divers. No recovery of sleep was observed in the postdive period. A difference in the effects on sleep by the dive depth was not found.