Does Breathing Nitrox Reduce Post-Dive Fatigue?

Nitrox has been claimed to improve blood oxygen circulation, reduce the severity of a barotrauma and reduce feelings of tiredness or fatigue following a dive. These are only anecdotal reports, and one controlled study with simulated dives in a dry chamber showed no measurable difference in fatigue, attention levels or ability to concentrate. A group of European researchers decided to test the hypothesis that post-dive fatigue is somehow related to decompression stress, assuming that it would be less in Nitrox-breathing divers.

The researchers tested 301 fit divers (204 male, 97 female) over a two-month period at the Red Sea resort town of Sharm- El-Sheikh, Egypt. Visually impaired divers had to wear corrective lenses during dives, and those using medications were excluded. Divers were forbidden from drinking alcohol or caffeine before and after dives. Each diver performed a single dive at least 12 hours after any previous dive, breathing either air or EANx32 (a mix of 32 percent oxygen, 68 percent nitrogen). No dive restrictions were imposed except a maximum depth of 100 feet. All divers did multi-level dives - - the Nitrox group ranged from 45 to 95 feet, with dive times between 32 and 69 minutes, while the air group dived between 40 and 90 feet, with dive times between 31 and 71 minutes. Divers followed their own dive computers (Nitrox divers' computers were set for an EANx32 mix) and were most often limited to a single safety stop of five minutes at 15 feet.

Fatigue was assessed before each dive and 30 to 60 minutes after, with each diver asked to evaluate both their energy and tiredness levels on a scale from 0 to 10. Then alertness was tested using critical flicker fusion frequency --"the frequency at which a stimulus of intermittent light seems to be completely stable to the observer." A waterproof device consisted of a rotating cylinder with a slit that allows the eye to see flickering. As the rotation of the cylinder speeds up, the eye and brain eventually cannot detect the flicker but sees a solid or fused light. The earlier this occurs, the less alertness and the more fatigue the viewer experiences. The test was repeated three times, with the mean value used as the fusion frequency.

The study showed a significant decrease in perceived fatigue in Nitrox divers. The flicker-to-fusion times decreased by 6 percent in the air group but increased 4 percent in the Nitrox group. On the other hand, the difference between breathing pre- and post-dive in Nitrox users was not significant. The critical flicker-fusion frequency measurements showed impairment in air divers but improvement in Nitrox divers. Still, more studies are needed to fully explore the complexity of modifications in the nervous system according to the type of gas used for a dive.

"Evaluation of critical flicker fusion frequency and perceived fatigue in divers after air and enriched air nitrox diving," Pierre Lafere et al., Diving and Hyperbaric Medicine, Vol. 40, No. 3, pages 114-117.