Evaluation of critical flicker fusion frequency and perceived fatigue in divers after air and enriched air nitrox diving.

Introduction: Many divers report less fatigue following dives breathing enriched air nitrox (EANx) compared with breathing air. A reduction of post-dive fatigue with EANx would suggest a pathological origin, possibly the presence of asymptomatic nitrogen bubbles in the body after a dive.

Method: We studied fatigue in 219 healthy divers performing either an air (n = 121) or EANx32 (oxygen 32%, nitrogen 68%; n = 98) dive to 21.2 ± 4 metres' sea water for 43.3 ± 8.6 minutes in tropical open-water conditions. Divers were assessed pre-dive and 30-60 minutes after surfacing using a visual analog scale (VAS) of fatigue and critical flicker fusion frequency (CFFF).

Results: The two groups were comparable in sex ratio, age and diving experience. The change in perceived fatigue level after a single dive was significantly lower when EANx was breathed compared to air dives (VAS; P < 0.001). Compared to pre-dive, CFFF decreased by 6% in the air group (P < 0.01) but increased by 4% in the EANx group (P < 0.05). The post-dive difference between the two groups was highly significant (P < 0.001).

Conclusions: Three hypotheses should be considered to explain the difference in post-dive fatigue and alertness between the air and EANx groups: a nitrogen effect, an oxygen effect and a bubble effect. These involve complex phenomena in the functional modifications of the nervous system in hyperbaric environments according to the type of gas used for the dive, and more research will be required to elucidate them.