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>On Thu, 22 Dec 1994, Prime Rat wrote: >> >> Recompression works because of the pharmacological effects of oxygen as >> opposed to the mechanical effects of pressure. Richard replies >What about all the successful air-only IWR cases, usually performed in ><20m max? Would all of these have been better-off breathing O2 on the >surface? Is it possible that, if dealt with within a few minutes of >symptoms, the hydrostatic pressure DOES matter? (Not a pointed >question...honest...) I think Richard has a valid point, as does Prime Rat. Prime Rat was trying to point out that O2 is a "drug" whose action is determined by it's inspired/arterial partial pressure, thus it does it's stuff (good, eg. reversing rheological changes associated with DCI???, or bad, eg. CNS toxicity) better at greater pressure. Prime Rat believes (right or wrong) that this is a conceptual point that some people overlook. As Richard implies, Prime Rat's assertion that the "mechanical" effects of pressure are unimportant is nonsense, as is a considerable portion of what Prime Rat posts, either used for emphasis, or due to his being a bitter, twisted, contrary soul because no one buys his book. Compression on air, as in Richard's anecdotes, will have two beneficial effects. Firstly, it will compress any bubbles, although, as I have posted numerous times, this effect will be small V=4/3 (pi r^3). Compression of bubbles may alleviate symptoms if the bubbles are causing tissue distortion etc. Reduction in size of the blood gas phase may reduce or prevent blood foaming and sludging etc., since there is likely a critical volume for DCI. Breathing air at an increased ambient pressure will increase the oxygen window (inherent unsaturation) between tissue bubbles and alveolar/venous gas. With increasing gas phase separation, the oxygen window tends to drive off-gassing and bubble shrinkage. For more information, buy my book. Thus, the hydrostatic pressure does matter. Compression of bubbles may reduce mechanical distortion of tissues and rheological changes. Compression even on air will be better than surface air breathing for bubble resolution, but not better than NBO or HBO which provides a bigger oxygen window. regards, David Doolette ddoolett@me*.ad*.ed*.au*
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