Does volume of air breathed change DCS risk?

[Artimas]

I don't know very much about decompression physiology and was wondering about the following question:

Assume there are 2 physically identical divers doing identical dives. One breathes faster and uses more air (nitrox, etc.) than the other.

Is the risk of DCI different for the 2 divers?

I assume no, that it's all based on partial pressures, but don't know and was wondering if I'm correct.

Thanks.

 

[Charlie99]

N2 absorption is primarily driven by partial pressures, just as you expected.

There is a minor difference in N2 loading associated with increased blood flow from higher exercise levels, but this is a secondary effect. Increased work levels while on the bottom increases blood flow, which effectively reduces the halftime of some tissues. Usually there is an associated increase in breathing rate associated with breathing hard. The dive computer manufacturer Uwatec has computers which monitor breathing rate to make a guess at exercise levels and then adjust the deco algorithm slightly to compensate. This is only of much importance in cases where a diver works hard on the bottom, and then is essentially motionless during ascent and decompression stops. But again, it's a secondary effect, and there is very little difference in nitrogen absorption whether one is hoovering away or merely sipping the air.

 

[Dr Deco]

Hi Artemas:

Depth of breathing does not change the nitrogen partial pressure levels in arterial blood.

However, physical activity which is often reflected in increase air usage, will increase blood flow. This increase is dramatic and can be TEN times the resting level.

 

[Artimas]

Thanks for the replies!

I was aware of the physical activity and blood flow aspect, but I was specifically wondering about the volume of gas breathed as the only variable. Perhaps I should have been more specific in my question, but I meant to imply that both divers would be under the same level of exertion (just to remove that as a variable).

Thank you very much for the replies. I sure have a lot to learn!