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Publication AbstractsEvolved gas, pain, the power law, and probability of hypobaric decompression sicknessConkin J, Foster PP, Powell MRAviat Space Environ Med 1998; 69:352-9 AbstractThe intensity of a pain-only decompression sickness (DCS) symptom with respect to time at altitude increases, peaks and then declines in some cases. A similar pattern is also seen in a graph of the probability density function [f(t)] for DCS. The f(t) is the proportion of DCS per unit time with respect to time at altitude. The integration of f(t) with respect to time provides the cumulative probability of DCS [P(DCS)]. We suspect that the perceived intensity of pain with a given stimulus intensity is related to the P(DCS); it may be related to the intensity of the stimulus to a power (alpha). Our stimuli are defined as pressure ratio (PR = (øP1N2 /P2) - 1] or pressure difference [deltaP = øP1N2 - P2], where øP1N2 is the N2 partial pressure calculated in the 360 min half-time (t½) compartment or t½ is estimated with other parameters and P2 is ambient pressure after the ascent. Both stimuli represent a potential released volume of gas. We tested the null hypothesis that alpha > 1 was no better than alpha = 1 in PRalpha and delta Palpha in a log logistic survival analysis of 1085 exposures in hypobaric chambers. The log likelihood number increased from -1198 for alpha = 0 for the null model to -724 for PRalpha when alpha = 3.52 with a 42 min t½ and -714 for deltaPalpha when alpha = 8.44 with a 91 min t½. We conclude that the improvement in our expressions for decompression dose with alpha > 1 is not by random chance and that alpha may link the physics of gas evolution to the biology of pain perception. Because of our empirical approach, we do not exclude other possible interpretations.
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