The relationship of inert gas and venous gas emboli to decompression sickness.

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The relationship of inert gas and venous gas emboli to decompression sickness.

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Title: The relationship of inert gas and venous gas emboli to decompression sickness.
Author: Shannon, JS
Abstract: INTRODUCTION: A preliminary Duke study of 552 dives suggested that VGE and Type II DCS (DCS-II) were more likely after helium (He) dives than after nitrogen (N2) dives (Vann, UHM 2003;30(3):Abstract 61). The present study investigated the relationships of inert gas, VGE, and DCS in a larger series of similar dives. METHODS: In 1985, the U.S. Navy tested 1,582 He-O2 dives (37 DCS-I, 22 DCS-II) and 837 N2-O2 dives (42 DCS-I, 8 DCS-II) (NEDU Reports 1-85; 8-85) and collected Doppler VGE data. We defined VGE with Spencer Scores of 3-4 as HBG (High Bubble Grade). We first used logistic regression to test inert gas type, HBG, and diver age as determinants of the outcome variables HBG, DCS-I, DCS-II, and DCS (DCS-I + DCS-II). We then added a measure of decompression stress (DS) to each of these analyses to account for differences among dive profiles. DS was defined as the DCS probability estimated by the U.S. Navy multi-gas exponential-linear model (LEM; NEDU Report 02-10). RESULTS: HBG and DCS-II were significantly higher for He than for N2 in tests of inert gas type, and all outcome variables increased significantly with decompression stress. The N2 DCS-I probability was nearly double that of He. At low DS, the He DCS-II probability exceeded that for N2, but at high DS, the N2 DCS-II probability exceeded that for He. The HBG probability was 1.6 times greater for He than for N2, and HBG increased slightly but significantly with diver age. When HBG were present, the estimated DCS probability was twice as great as without HBG. DISCUSSION: LEM estimates were significant predictors of decompression stress but did not fully account for inert gas type. DCS-I and DCS-II should be modeled as different outcomes. HBG was a useful indicator of dives with elevated DCS probability.
Description: MS Thesis
URI: http://archive.rubicon-foundation.org/3431
Date: 2003

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