How conserve air when necessary

[crookshanky]

Hello Crookshanky
This is not correct. If it were, then it would be impossible for us to dive because the PCO2 in our bodies would be multiplied many times as we descend and this would rapidly prove fatal. CO2 in the body is a dissolved gas in a non-compressible space (fluid) and its partial pressure is therefore unaffected by changes in ambient pressure...

Is the partial pressure law not applicable because the dissolved CO2 in the blood is in liquid phase? Is the narcotic effect of a substance a factor of it's molar concentration in the blood/tissues?

...Essentially correct. As the partial pressure of a narcotic gas increases, then so too will its narcotic effect. My point (as above) was that this does not occur simply as a function of ambient pressure in relation to CO2. For the CO2 partial pressure in the body to increase you either have to:

1. Not move enough fresh gas in and out of the lungs (ie, breathe enough) to eliminate the CO2 that the body is producing; or

2. Actually have CO2 in the inhaled gas so that breathing becomes very inefficient at removing CO2. This can happen in a rebreather...

Is the narcotic effect related to ambient pressure in the case of the inhalation of CO2 (ie. inhalation of a given volume concentration at greater depths would cause greater narcotic effects)? If so, is this a result of the increased effective concentration in the lungs (because of higher partial pressure) and subsequent increase in CO2 diffusion rate into the blood?

Is the narcotic effect of CO2 during breath holding independent of depth (ie. dependent upon metabolic rate only)?

...The physiological basis for the first cause is complex, and is discussed in this lecture which I gave at the Southern Africa Undersea and Hyperbaric Medical Association Meeting several years ago...

I had been meaning to watch that. Always enjoy your talks. I had never before heard a technical explanation of the presumed cause of Shaw's accident.

Thanks very much for your participation on this forum. Very grateful to have such expert help on these topics.

 

[Bob DBF]

I think the suggestion is to breathe out into the BCD, than back in your lungs, like reabreathe the air some cycles before you breathe it out and take in new air. Not that the amount of air you carry in your BCD should act as a pony-bottle.

Depending on the size and length of the hose to the BC and how deeply you breathe, you may get little to none of your BC air but just recycle that in the hose. I might try it, if there was nothing else, but would expect a CO2 hit and then a lung infection if I survived. Nothing I would train for, and I was ingrained not to use BC "air" back in the day of CO2 inflators.


Bob