The Influence of Thermal Exposure on Diver Susceptibility to Decompression Sickness.

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The Influence of Thermal Exposure on Diver Susceptibility to Decompression Sickness.

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Title: The Influence of Thermal Exposure on Diver Susceptibility to Decompression Sickness.
Author: Gerth, WA; Ruterbusch, VL; Long, ET
Abstract: The incidences of decompression sickness (DCS) were compared in divers who completed air decompression dives while fully immersed in water at temperature controlled independently [either warm (36.1 °C, 97 °F) or cold (26.7 °C, 80 °F)] during bottom time (BT) and decompression phases. Divers wore only loosely fitting swim trunks, t-shirts, and neoprene boots and dive gloves, performed cycle ergometer exercise while at bottom. rested during decompression, and remained under controlled resting conditions at 78 ± 5 °F (25.6 ± 2.8 °C) during the immediate 4 hr postdive period when they were monitored for central venous gas emboli (VGE) with 2-D cardiac echo imaging. Four hundred man-dives were completed with 21 diagnosed cases of DCS in seven series of dives to 120 feet of seawater (fsw) with different combinations of thermal conditions and BT from 25 to 70 min, but with the same U.S. Navy Standard Air 120 fsw/ 7O min (depth/BT) decompression schedule (stops: 30 fsw/9 min, 20 fsw/23 min, 10 fsw/55 min). Observed effects of water temperature on DCS risk during BT (Tw,b), water temperature during decompression (Tw,d), and different BT were isolated with a fitted logistic model. The DCS odds ratio for a 10°C increase in Twb was 23.8 (95% CI = 3.8-131.5), while the odds ratio for a 10 °C increase in Twd was 0.01 (95% CI = 0.002-0.114). In another series of 84 man-dives to 150 fsw and BT = 60 min, divers were cold during compression and bottom phases and warm during subsequent decompression on a U.S. Navy Standard Air 150 fsw/ 60 min schedule (stops: 40 fsw/ 3 min, 30 fsw/ 19 min, 20 fsw/ 26 min, 10 fsw/ 62 min). With only a single case of DCS, the DCS incidence in this series was significantly lower (P<0.001) than obtained in a series of 150 fsw/ 60 min dives (5 DCS in 20 man-dives) conducted in an earlier study with divers cold throughout the dives and decompressed on a schedule nearly 2.5 times longer. Postdive VGE scores were only weakly associated with DCS occurrence, with maximum VGE grades of 3 or 4 after flexion of any limb providing the best positive predictive values (PPV, area under PPV curve = 0.62). The area under the receiver-operator characteristic (ROC) curve for maximum VGE grades after flexion of any limb was only 0.61. Beneficial effects of warm conditions during decompression were more pronounced than deleterious effects of warm conditions during BT, while effects of a 10°C increase in Twd were comparable to effects of halving BT.
Description: Citation Status: Active; Citation Classification: Unclassified; Title Classification: Unclassified; Report Classification: Unclassified; Identifier Classification: Unclassified; Abstract Classification: Unclassified; Distribution Limitation(s): 01 - APPROVED FOR PUBLIC RELEASE; Information provided by the Department of Defense and the Defense Technical Information Center (http://www.dtic.mil/) is considered public information and may be distributed or copied unless otherwise specified. Use of appropriate byline/photo/image credits is requested.
URI: http://archive.rubicon-foundation.org/5063
Date: 2007

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