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> 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). I actually wouldn't consider setpoints of 1.2-1.4 to be conservative for rebreathers, but that's another issue... > 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. Curt, Thanks for the input. I agree, the issuse of O2 exposure using constant PO2-rebreathers is more directly related to symptoms of "chronic" oxygen toxicity. While cumulative effects may lead to long-term damage, I am not nearly as concerned with these as I am with convulsions from "CNS" Oxygen toxicity. However, my understanding is that the probability of an O2-induced convulsion increases with increased (recent) cumulative oxygen exposure, and that the rationale for air breaks at all is to reduce the probability of a convulsion during the final decompression stops, after a substantial (recent) cumulative O2 "dose". I'm not familiar with the notion of FO2-related (as opposed to PO2-related) acute alveolar toxicity, so maybe I've been wrong about this.... It's just that I never see anyone discussing concerns about cumulative O2 dose on rebreathers, and what steps should be done to alleviate it. Aloha, Rich Richard Pyle deepreef@bi*.bi*.ha*.or* ******************************************************************* "WHATEVER happens to you when you willingly go underwater is COMPLETELY and ENTIRELY your own responsibility! If you cannot accept this responsibility, stay out of the water!" *******************************************************************
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