Does Nitrox help air consumption?

[Dive Source]

I read article in Rodales a couple years ago about test they did with divers on 36 mix vs the same divers on air ( anybody remember this? I can't find it on Rodales site)

If memory serves me they said their results showed a definate lowering of breathing rates with the 36 mix over air.

Personally I haven't noticed it, but then again I never thought much about it, I do believe I am less tired at the end of the day and if that's just a placebo please don't tell my body cause I like tricking it

 

[Don Burke]

In at least one study, they found that divers swimming hard at shallow depths had better gas consumption with EAN36. My guess is that the extra oxygen was making up for regulators that weren't delivering enough gas.

 

[CD_in_Chitown]

I have noticed better consumption on mix but nothing as startling as what you saw going from .9X to .5X. I think you probably worked the nerves out on the first trip and were more comfortable in the water the second dive. That is where I see my biggest gains in RMV. If I'm diving new/unfamiliar kit, unfamiliar buddy, and especially with students the consumption is much greater than dives with me and my regular buddies.

 

[Warren_L]

Interesting thought about the SAC not being affected as much on Nitrox when swimming hard - that I have yet to measure. My average SAC is around 0.5 on both air and nitrox, but I wonder if the nitrox would keep my SAC from going up as high as when breathing air when working hard...

 

[rdriver]

I also Have noticed longer bottom times using the same size and pressure tank than with 21% Also Notice less fatigue after a dive too...... I know a lot of experts say it's not possible ...but this is just my O2 cent worth
Rob

 

[DA Aquamaster]

I have noted a reduction in gas consumption with Nitrox. My SAC is already good at about .5 and my spouses SAC is very similar. On a swim intensive dive the usual 100 to 200 psi difference between our tank pressures at the end of the dive will jump to around 800 to 1000 psi. when I use nitrox and she remains on air.

My personal unproven theory on this subject is that nitrox creates the potential to lower you breathing rate, but to really benefit from it requires the diver to tolerate an elevated level of CO2 as less exalation is done during the dive. Minimizing CO2 buildup with the lower breathing rate also requires some focus on deeper than normal exhalation to vent the residual CO2 more efficiently over the fewer exhalations made during the dive.

I started diving as a free diver in 1979 and still freedive frequently during the summer. I also spent a lot of time spearfishing on scuba which in my neck of the woods means setting on the bottom skip breathing (I know, I know it's a scuba sin). Both activities tend to develop CO2 tolerance in a diver.

The US Navy did it's original enriched air studies in the 50's with helmet divers, who due to the poorly ventilated equipment of the time also tended to have high exposure to CO2 and over time a high tolerance to elevated CO2 levels. The Navy discovered that elevated CO2 increased a diver's suceptibility to an oxtox hit and due to the unpredicatble nature of this, shelved the whole enriched air idea for a couple decades.

My conclusion is that if you are getting extra gas milage out of Nitrox, you probably want to be very careful with your max PO2 and consider limiting the working portions of the dive to a PO2 of 1.4 rather than the 1.6 accepted by many agencies.

 

[donclaypool]

Good Hypothesis, DA. Thanks for the input from all. I'd like to find that Rodales article. It will be interesting to do a little more research on this topic.

Don

 

[String]

A few of my ideas on this:

Firstly, even on 21% you have far too much oxygen per breathe than you need so increasing that does NOT affect the amount or frequency you need to breathe. Exhaled gas on 21% is still over 16% O2 meaning youve used a tiny fraction.

Breathing reflex is (to all intents and purposes here) CO2 mediated (ok, i know its pH based really...).

Having established that there is no oxygen shortage as such in my view the same amount of effort leading to the same amount of metabolism will have an identical rate of CO2 production and therefore identical breathing times and amounts.
Consequently, i cant see how it could affect the rate.

At these levels, CO2 production rate is governed solely by metabolism as oxygen is not the limiting factor.

For what its worth i dont think ive ever seen any proper reviewed research published stating that EAN reduces SAC and the like.

The "feeling less tired after a dive" that someone mentioned is a different issue all together - thats related to possible sub clinical DCS and there is a valid physiological mechanism to justify this HOWEVER again research has failed to be conclusive about this so any effects may be so small other factors mask them totally.

There is one thing medical studies prove time and time again though - never underestimate the strength of the placebo effect.

FWIW ive only ever done 1 nitrox dive and my SAC for the dive was smack on average for the rest of my diving in those conditions. A sample size of 1 isnt exactly representative though

 

[yoda4x4]

To the believers and non-believers, here's my thoughts.

Believer's: If your SAC has gone down while using Nitrox... GREAT. Keep using it.

Non-believer's: Use Nitrox for the extended bottom time that it's been PROVEN to provide.

Whatever the case, do what works best for you.

Just my $0.02.

David

 

[Toolbox-13]

I have also noted less air consumption with Nitrox and I also feel less fatigue after the dive.