Posted by H on January 29, 2003 at 11:46:26:
In Reply to: purging CO2 from your blood, muscles, and lungs posted by Karl S. on January 28, 2003 at 15:32:07:
I see the obvious benefit of the purging while freediving, although at the risk of SWB. However, given that physiologists estimate the average human produces 200cc of CO2 per minute, I fail to see the physiologic mechanism by which "purging" CO2 can last during scuba. Assuming a 60fpm descent rate, your muscles and tissues will have produced, if you are an average human, 200cc of CO2. Now, if you dump the blood CO2 concentration, I can see where the increased gradient would speed the diffusion of CO2 into the bloodstream. But again, given the time scales involved this doesn't seem significant.
According to researchers in Italy studying lung blockages, the average length of time it takes for a person at the surface, breathing pure O2, to exhale less than 2.5% N2 is 7 minutes. That means, that upon cessation of breathing N2, the lungs hold and continue to dispell (there is a small component of N2 exiting the bloodstream as well) N2 for that length of time.
Another problem with your CO2 blowdown theory is that it has been well documented that hyperventilation and CO2 reduction affects blood pH. That change has a large negative effect on muscle performance. You risk increased immune response, which will then increase the complement damage from decompression stress. Although I think that theory also suffers from time scale problems in this discussion ;-)
It has been shown in a peer reviewed study that divers subjected to several "narcotic" instances in chambers of a period of time *felt* that they were less impaired, but in reality were equally affected. This is a real danger of playing the narcosis game. With the availability of appropriate gasses, I fail to see why anyone would resort to disproven gimicks.
There is great benefit to relaxing on the surface prior to descent. But I don't think that long term (as in minutes) CO2 reduction is one of them. It sounds psychosomatic to me.