Mailing List Archive Mailing List Archive
THE O2 PARADOX: The goal of decompression is elimination of offending inert gas. To that end, it is widely held that decompression using 100% O2 will increase the efficacy of decompression. That tenet derives from the notion that reduction of inert gas in alveolar space when breathing pure O2, will, through a concomitant Le Chatelier principlesque increased egress of inert gas from blood perfusing the alveoli, reduce the offending gas. Indeed O2 decompression has been employed to reduce required decompression time and also has been shown to reduce DCI in a series of dives. However, this simple model is complicated by the impact of high ppO2 on perfusion which has a direct effect on inert gas elimination. O2 is known to be a potent cerebral vasoconstrictor and as ppO2 inhaled increases, perfusion may be reduced. An evidence to this is the decrease in cardiac output that accompanies increases in ppO2 inhaled. Measurement of blood flow to arm and leg under those conditions have also shown a reduced perfusion. Yet earlier studies had shown that immersion increased inert gas elimination. This was ascribed to immersion mediated redistribution of blood with increased cardiac output. On the other hand hypoxia increased N2 elimination. A subsequent study, in a series of studies where ppO2 ranging from 0.12 to 2.5 ATA bore out the contention that N2 elimination was inversely related to ppO2. However the subjects were not dove prior to gas elimination study. How does 100% O2 contribute to the amelioration of the effects of DCI then? Although such an explanation fails to account for the particulars of the thrombi-like bodies projected to form in response to bubbles, it is possible to invoke that the presence of bubbles, which are now foci of N2 gas that 'degas' more readily when dissolved N2 is reduced by a N2 free alveolar or circulatory environment, contribute to the positive effects of O2 on DCI. The above cited study did not 'decompress' subjects per say, thus the actual 'bubble' formation potency of the procedure was not addressed. Furthermore a 'hypoxia' mediated increase in N2 elimination in a simulated altitude study did not control for vascular bubble formation, which would have had the same effect. Yes the paradox remains but O2 works for DCI and in reducing the incidence of DCI, as well as assisting in its therapy! On the other hand use of nitroxes of various blends for decompression need to be studied more carefully. Regards Esat Atikkan
Navigate by Author:
[Previous]
[Next]
[Author Search Index]
Navigate by Subject:
[Previous]
[Next]
[Subject Search Index]
[Send Reply] [Send Message with New Topic]
[Search Selection] [Mailing List Home] [Home]