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If memory serve me right (my paper are still packed from moving) we are actually talking about three (3) types of effects from high PP02. 1. Acute Pulmonary (Aveolar) Oxygen Toxicity 2. Oxygen Toxicity 3. Whole Body Oxygen Toxicity Air breaks when breathing 100% O2 are predominantly to limit the potential of acute pulmonary (aveolar) oxygen toxicity which is characterized by loss of aveolar function (toxicity damage to aveolar) without other symptoms of general oxygen toxicity. If memory sevres me correctly this is principally a concern with high % O2 and increasing diluent gas % even with high PPO2 decreases the risk which is why air breaks are not usually included when using mixes with <80% O2. Symptoms of oxygen toxicity as we normally consider it do not include acute aveolar damage and produces sysmptoms more closely associated with the CNS. Onset is generally attributed to exposure to high PP02 and time, and is not related to the actual % O2 in the mix. Whole body oxygen toxicity is a function of the cumulative exposure and toxic effects of prolonged exposure to high PPO2. Rich, I have not seen any reports that indicate problems with oxygen toxicity or acute pulmonary oxygen toxicity when using rebreathers with conservative PPO2 set points (1.2-1.4). You may want to determine the max % O2 your breathing at shallow stops to evaulate your potential for acute pulmonary toxicity and consider periodic changes in your PPO2 setpoint as you mentioned. I would be more concerned about your whole body oxygen toxicity exposure which you indicated may exceed the recommended total exposure for a single dive. The frequency of these exposures may lead to cummulative damage that the body is not able to repair between exposures. CNS damage and loss of andaveolar function can occur with excesses whole body O2 exposure and would be my primary concern. Thats my $0.02 from buried memory. Curt Curt W. Smitka Phone: (313) 747-0252 Administrative Manager Fax: (313) 936-8620 Reproductive Sciences Program Email: cwsmitka@um*.ed* University of Michigan 11th Floor, 300 N. Ingalls Bldg. Ann Arbor, MI 48109-0404
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