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Rich, My purpose here is not to add *unknown*, or more accurately unquantifiable variables to the algorithms of nitrogen absorption, but to add a *known* variable, using straightforward pharmacokinetic principles. Over the past twenty years, the science of pharmacokinetics, the study of distribution and elimination of drugs has entered into the mainstream of medical care. Most drugs we ingest (like nitrogen) have some leeway between the therapeutic and toxic doses. Chaos math may have some application in determining stochastic events (like sudden, life threatening allergy to a drug) but most of the time, pharmacokinetic modeling (just like N2 absorption algorithms) deal with what happens to most folks. The Navy and other tables for NDL were developed empirically, tested and modified by actual experience. This is analogous to Phase I testing of a new drug. DAN is collecting data and profiles on a million "sport" dives. This is similar to post-marketing testing of a drug; N2 in this case. Now if you believe that all DCI events are stochastic then the latter type of study or analyses of the data will not be helpful in preventing them. Similarly, we can postulate all sorts and types of other variables that *may* affect the incidence of DCI. But the pharmacokinetics of nitrogen is what the tables (and algorithms) are all about. This is not a *new* variable like, say the effect of complement on bubble mechanics. My point is this: You cannot accurately model the distribution and elimination of a drug without knowing the volume of distribution (Vd) in the body of that drug. You can't determine the Vd unless you know something about the size of that "body" i.e.,person. If the relative concentration of the drug is small in relationship to the volume of distribution, big variations in body mass can occur without changing the concentration greatly. A two fold increase in Vd halves the concentration, but if it goes from 0.008 mg/dl to 0.004 mg/dl, it probably won't have much biologic/pharmacologic effect. But nitrogen is present in high concentration in our bodies (~79%, maybe less). So differences in body size and so Vd are likely to play a *great* role in N2 elimination. It wasn't taken into account in the tables, because without some way of measuring the number of breaths taken at a given depth, not just the total gas breathed, it is almost impossible to know whether you were on-gassing or off-gassing a compartment at that moment. But now with air integrated computers, it is possible. I still think that the tables can be improved through the application of other medical disciplines, anesthesiology, physiology, pharmacology. I may be wrong, but I'll learn a lot trying. Safer diving through wiser physiology Peter Heseltine
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