Nitrox and post dive fatigue

[rcohn]

Dr. Deco,

I'm wondering if you might have any insight in to following question.

I know when I dive nitrox, I don't notice any difference in post dive fatigue. However, friends report a marked improvement in both fatigue and headaches on dives as shallow as 60 or 70 ft. I know some believe the fatigue is a form of sub-clinical DCS, do you agree? Also, do the different experiences indicate anything about an individual diver's susceptibility to DCS?

Thanks,

Ralph

 

[Dr Deco]

From what I have heard, there is indeed a difference in response among some divers to nitrox compared to air. As with many things in diving, there are marked differences among individuals.

The question of post-dive fatigue is truly an intriguing one, and it does not have an answer at the moment. As is true with many questions in science, where there are few answers, there exist a plethora of hypotheses. To my knowledge, no dedicated study to this particular problem has been performed.

Subclinical decompression sickness has been proposed as a possibility. This would result from the “silent bubbles” that were first proposed by Dr. Al Behnke in 1942 (Investigation concerned with problems of high altitude flying and deep diving; application of certain findings pertaining to physical fitness to the general military service. Milit. Surg. 90, 9 - 28.) In altitude research studies during WW II, it was noted that fatigue, sometimes profound, occasionally followed depressurization, and it often accompanied other manifestation of decompression sickness.

Fatigue can also occur as the only symptom. When this happens, some have noted that the fatigue remits with repressurization. This is suggestive of a role of gas bubbles someplace in the body.

It is truly speculative that individuals experiencing fatigue are more susceptible to frank (= clinical) DCS. I personally do not know of any study (or experience from the field) that suggests this to be the case.

If fatigue did have its etiology (= cause) in gas phase formation, then one could imagine that nitrox, with its lower partial pressure of nitrogen, would be protective. I believe that the jury is still out on this one.