Posted by Elaine on October 26, 2004 at 15:36:03:
In Reply to: Re: Was this diver using a rebreather? posted by MHK on October 26, 2004 at 14:55:57:
Just trying to make it simple.
Assuming an untainted air fil the air in a tank is composed of approximately 78% Nitrogen, 21% Oxygen, and the remaining 1% or so contains other gasses such as hydrogen, argon, neon, krypton (really), and CO2.
CO2 is a waste product of metabolism. Increasing exertion increases the amount of this waste product (CO2) in the body. The fastest and most efficient way that the body can eliminate excess CO2 is to increase ventilation. Ventilation can be increased by increasing respiratory rate or tidal volume (tidal volume is the amount of air which is excanged with each respiration), or both. The funcitional residual capacity (the amount of air in the lung which is not excanged) may eventually increase and lead to some of the problems that you describe. When you run out of air it your FRC (funcitional residual capacity)increases a lot :(.
So basically, his regulator may not have been able to supply the amount of "ventilation" his body required to blow off the metabolic waste product (CO2). Elevated CO2 is the second strongest stimulator of respiration in animals, lack of 02 being the strongest in healthy human beings. The experience of dyspnea occurs when C02 levels are elevated or 02 levels are depleated, with the elevated C02 being a culprit in "overbreathing" a regulator. The feeling of dyspnea is associated with panic in health humans and a potential for a rapid downward spiral in scuba divers.
I feel very sorry for the guy, his family and loved ones.