[abstract] MECHANISMS OF EXTENSION OF HBO2 TOLERANCE BY INTERMITTENT AIR BREAKS.

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[abstract] MECHANISMS OF EXTENSION OF HBO2 TOLERANCE BY INTERMITTENT AIR BREAKS.

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Title: [abstract] MECHANISMS OF EXTENSION OF HBO2 TOLERANCE BY INTERMITTENT AIR BREAKS.
Author: Chavko, M; Mahon, RT; McCarron, RM
Abstract: BACKGROUND: Intermittent exposure to air is used as a protective strategy against hyperbaric O2 (HBO2) toxicity. Little is known about optimal intermittent exposure schedules and the mechanism of protection. MATERIAL AND METHODS: One group of rats was exposed continuously to 2.8 ATA O2 until death. Other groups were exposed to 30, 60, 120 or 180 min intervals of HBO2 with different numbers of intermittent 20 min air breaks (1-12 breaks). After the final break, animals were exposed to HBO2 until death. In a separate experiment, animals were sacrificed before terminal exposure and lung tissue was collected for analysis of different gene expression. RESULTS: In all intermittent exposure schedules, the maximum O2 survival time was significantly longer, approximately 11 h compared with 7-8 h in the continuous exposure group. The number of air breaks required for developing tolerance varied with the length of the HBO2 interval. However, total HBO2 time required for tolerance formation was the same, 6 h in all intermittent groups (12 breaks in 30 min schedule, 6 breaks in 60 min schedule and 3 breaks in 120 min intermittent schedule). After reaching maximum, the survival time started to decrease, indicating a turning point in HBO2 exposure, from tolerance to toxicity. Continuous exposure to HBO2 resulted in an increase in lung protein nitration as a marker of toxic peroxynitrite formation. The mechanism of this increase involves activation of inducible NOS (iNOS). Both the increase in protein nitration and iNOS activation was eliminated by intermittent air breaks. CONCLUSIONS: Results show that: a) threshold duration of HBO2 exposure is required for tolerance formation by intermittency, b) tolerance is formed within a time “window” of HBO2 exposure, and c) intermittent air breaks inhibit iNOS activation and increase in protein nitration. (Supported by ONR Award No: N0001406WR20022)
Description: Abstract of the Undersea and Hyperbaric Medical Society, Inc. Annual Scientific Meeting held June 14-16, 2007. Ritz-Carlton Kapalua Maui, Hawaii (http:www.uhms.org)
URI: http://archive.rubicon-foundation.org/5206
Date: 2007

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  • UHMS Meeting Abstracts
    This is a collection of the published abstracts from the Undersea and Hyperbaric Medical Society (UHMS) annual meetings.

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