Monday, July 18, 2011

On Hidden Feedback Systems

I used to teach scuba diving.  This led me to a study of the effects of breathing gasses under pressure. 

In the early twentieth century, J. B. S. Haldane came to the conclusion that different “compartments” of the body (different tissue types) dissolved and released gasses such as nitrogen at different rates.  His work led to the Dive Tables used by the Navy and sport divers today.  The tables give empirically derived values for the amount of time that a diver can spend at a given depth and the rate at which he can ascend to the surface without the risk of dangerous bubble formation in the tissues.

In my own analysis, attempting to work from first principles, I was never able to prove that any change in atmospheric pressure was safe. This is not a matter of physics or chemistry, or even biology, per se.

The human body contains many interlocking feedback systems, governing the distribution of oxygen, removal of carbon dioxide, balancing electrolytes and enzymes, maintaining temperature and controlling digestion and excretion.  All are the product of billions of years of evolutionary selection for individuals that did not die when a low-pressure weather system passed by.
People die when a biological feedback system hits its limit and is no longer able to compensate for current conditions.  The problem is that these feedback systems are completely hidden from view.  The empirical tests conducted on 20-year-old Navy SEALs do not generally apply to 50-year-old overweight smokers in a dive class. 

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