Nitrox question for Dr. Deco

[fisherdvm]

View Poll Results: How does nitrox make you feel?
No different than air. 74 41.57%
Makes me less tired than air. 89 50.00%
Makes me more energetic than air. 15 8.43%
Makes me feel worse than air. 0 0%
Voters: 178.

With 58.43% believing that nitrox makes them less tired/more energetic than air, do you believe that subclinical DCS is at play here, or is it all a placebo effect?

I read that the deco tables were derived from doppler ultrasound studies demonstrating nitrogen bubbles, however, what do you think the smaller bubbles below the resolution of the ultrasound is doing to small capillaries, small arterioles?

Could it be that our dive tables are not conservative enough for up to 58% of the diving population?

 

[ianr33]

Could it be that our dive tables are not conservative enough for up to 58% of the diving population?

IMHO it is more likely that 58% of the diving population are not paying proper attention to deep stops and ascent rates.

I used to feel better after diving nitrox,nowadays I do slower ascents and more stops and can not tell the difference.

If you push the tables to the limits(100 feet for 20 minutes,direct ascent to 15 feet,3 minute safety stop then surface) you probably won't get bent but you might feel tired afterwards.

 

[fisherdvm]

IMHO it is more likely that 58% of the diving population are not paying proper attention to deep stops and ascent rates.

.

You might have a point, as I recall, a study indicated that up to 1/2 of divers ascend faster than they should. I personally have noted this myself when paired up with unfamiliar diving buddies. One guy tried to force me to ascend faster by grabbing my BC inflator and injecting more air. I almost slugged him for it.. He was very embarrassed on the surfaced when we reviewed methods of ascent.

However, I think that the deco table might not be conservative enough for people with existing undiagnosed medical conditions.

My question to Dr. Deco is, just because you can not see the bubbles on ultrasound, how do we know if the smallest bubbles (bigger than a capillary) doesn't cause non specific inflammatory reaction in the organs and tissues releasing inflammatory mediators that causes "fatigue", without causing the clinical signs we use to define DCS.

 

[The Kraken]

Wouldn't "more energetic" and "less tired" be pretty much the same thing???

the K

 

[Gene_Hobbs]

My question to Dr. Deco is, just because you can not see the bubbles on ultrasound, how do we know if the smallest bubbles (bigger than a capillary) doesn't cause non specific inflammatory reaction in the organs and tissues releasing inflammatory mediators that causes "fatigue", without causing the clinical signs we use to define DCS.

You are getting at my biggest area of interest for research going forward.

I have been very intrigued by idea of neurocognitive function following cardiac surgery for years. That is probably a function of being at Duke and the work on this topic that has occurred here. When I started at Duke I used to go to the Cardiac Anesthesia Rounds every week. It was interesting to me that these guys were seeing the emboli (gas, fat, gunk - my technical term, etc...) after every surgery. The cranial doppler signal on these patients sounded similar to signals I had heard on research subjects after dives. After a while I started seeing the work on neurocognitive function changes that could be teased out of people that showed no outward symptoms and would have gone totally unnoticed in the previous years. Then work seemed to focus on biomarkers to explain these changes. Since that time I have followed this literature intently hoping that one day we would be able to apply some of these techniques to our dives in the field. I think we are getting closer but we are not there yet.

Pulling back to topic, this is an interesting paper that was only ever published as a thesis.
Doppler Detection of Silent Venous Gas Emboli in Non-Decompression Diving Involving Safety Stops.
Uguccioni, D. 1994
RRR ID: 3430
Anyone else think we would see similar results on similar profiles using air vs. nitrox?

If anyone is really interested in what I was talking about above with Biomarkers, I would suggest the a book chapter: Grocott HP, Laskowitz D, Newman MF. Markers of cerebral injury. In: Newman S, Harrison M, eds. The Brain and Cardiac Surgery. London, England: Harwood Academic Press; 1999: 113-141.

 

[fisherdvm]

Wouldn't "more energetic" and "less tired" be pretty much the same thing???

the K

Some like pink, some like rose ... In this case, I just wanted to annoy you.

 

[The Kraken]

Congrats, you did !!!!

the K-ontrary Cuss

 

[TSandM]

You know, it's an interesting thought about inflammatory mediators and subjective fatigue. One of the common symptoms of autoimmune diseases like rheumatoid arthritis and lupus is profound and persistent fatigue. If, in fact, small bubbles are activating complement or otherwise exciting an immune response, it's not inconceivable that fatigue could be a manifestation of this.

 

[MSilvia]

Could it be that our dive tables are not conservative enough for up to 58% of the diving population?

Could it also/instead be that the air tables are not conservative enough, but the nitrox tables are?
After all, it seems as though the acaecdotal reports of 58% of surveyed nitrox divers would seem to indicate that they experience a lower incidence/severity of subclinical DCS than when breathing air.

 

[miketsp]

View Poll Results: How does nitrox make you feel?
No different than air. 74 41.57%
Makes me less tired than air. 89 50.00%
Makes me more energetic than air. 15 8.43%
Makes me feel worse than air. 0 0%
Voters: 178.

With 58.43% believing that nitrox makes them less tired/more energetic than air, do you believe that subclinical DCS is at play here, or is it all a placebo effect?

I read that the deco tables were derived from doppler ultrasound studies demonstrating nitrogen bubbles, however, what do you think the smaller bubbles below the resolution of the ultrasound is doing to small capillaries, small arterioles?

Could it be that our dive tables are not conservative enough for up to 58% of the diving population?

There's probably quite a bit of placebo effect here.

Plus it probably depends on how you use the stuff. Some people deliberately dive air tables with Nitrox as an added safety factor. Many end up diving near air profile because their SAC isn't good enough to get significantly extended dive times on an AL80. And those with decent SACs tend to push the profiles to the limit and still get back on the boat with half a tank.

So a simple poll result without correlation of the profile probably doesn't mean anything.

Then again, as far as fatigue goes, I made a post some time ago with an attachment of a report of a double blind controlled test done with firemen breathing air or Nitrox without knowing what they were actually breathing and the conclusion was that at low and normal activity levels there was no difference while at high exertion rates (aerobic level) there was a fatigue reduction.

Given the very low incidence of DCS cases per thousand dives I find it hard to believe that dive tables are anything other than conservative and your suggestion that they are not conservative enough for 58% of the population does not seem reasonable to me. If we had 58% with sub-clinical effects then on a normal distribution curve we'd expect a lot more serious cases.