Capt Jim Wyatt
Hanging at the 10 Foot Stop
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There is no empirical evidence to support this, only anecdotal.
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There is no empirical evidence to support this, only anecdotal.
You often hear it said that when using nitrox, you either get more safety (by diving nitrox to air limits) or more bottom time (by diving nitrox to nitrox limits). You can't get safety and more bottom time. A recent article in Dive Training magazine stated exactly that. It's safety or extended bottom time--take your pick.
I find that curious.
Let's say I am planning a dive to 70 feet. If I am diving on air, according to the PADI RDP my maximum NDL is 40 minutes. Let's say that I instead use 36% nitrox. In that case, my NDL is 75 minutes--considerably more.
So what if I dive for 50 minutes? That is nowhere near the NDL for nitrox 36, and it certainly looks to me to be an extended bottom time.
A ScubaBoard Staff Message...
This would be a good one for the "Ask Dr. Decompression" forum.
The reason that nitrox reduces fatigue is because it reduces "decompression stress", or subclinical symptoms of DCI.
There are a whole host of things that happen in our bodies when we are offgassing, and one of them is an immune response to the microbubbles. Of course, an immune response in the blood results in the lymphatic system having to carry off the excess dead white cells produced to mount the attack. The immune response itself, as well as the lymphatic aftermath, both serve to create fatigue, stiffness, perhaps sore muscles, etc...
Remember... we're talking subclinical DCS. Just as "every dive is a decompression dive", you could also say that after every dive we are all a "little bit bent". Back in OW-101, wasn't fatigue taught to us as being one of the signs of DCS?
It is generally the second symptom... right after denial.
Nitrox can help to reduce this.
Until you take advantage of the extended bottom times available from nitrox... then you're back to square 1 with a full nitrogen load.
Similar benefits to nitrox have been reported by divers adding deep stops to their profiles.
Hello Readers:
Nitrox vs. Air
The jury seems to be out on this. I suspect it is, as pointed out by one responder, related to the profile and its stress. The Undersea and Hyperbaric Medicine article quoted above did not have a very stressful profile. [I pointed that out as one reviewer of this paper.] These dives would not make a very definitive test of the hypothesis. :06:
Most people seem to implicate the growth of microbubbles, and the prevention of this by reducing the nitrogen in the breathing mix. It is curious that slowing ascents and deep stops produce the same, or similar effects.
Dr Deco :doctor:
Readers, please note the next class in Decompression Physiology :1book:
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Michael R. Powell, M.S., Ph.D.