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---------- Forwarded message ---------- Date: Thu, 27 Jun 1996 09:27:29 +0930 (CST) From: David Doolette <ddoolett@me*.ad*.ed*.au*> To: "Peter N.R. Heseltine" <heseltin@hs*.us*.ed*> Subject: Re: CCRs and the *right* computer >Peter wrote: >Basically I'm asking if all that matters is the pPN2 or if the relative >concentrations of other gasses, have an effect on the absorption of >nitrogen (..like the oxygen window effect). Yes and no. Presence of a third gas can cause concentration effects, like the second (or is it third) gas effect with N2O anaesthesia. In other words the alveolar partial pressure of gases can be altered by rapid inert gas uptake or elution. With trimix diving, the helium can exert such effects since it is likely to diffuse more rapidly than oxygen or nitrogen. At the switch off of helium, rapid helium transfer into the lungs can reduce PAO2 and PAN2, the former a problem as dilutional hypoxia can result if a low FIO2 is used at this switch and the opposite might occur with a switch to helium. This effect is probably rather small with a relatively insoluble inert gas like helium compared to the problems with the more soluble N2O with which the total mass of gas flux is greater. More to your point, PAO2 /PaO2 (and remember this is relatively close to PIO2 at depth) is well known to alter the whole body elution (and presumably uptake) of nitrogen [1]. SiInce the mean PIO2 is kept constant in C2 diving this is not much of a problem. 1 Anderson, D., Nagasawa, G., Norfleet, W., Olszowka, A. and Lundgren, C. O2 pressures between 0.12 and 2.5 atm abs, circulatory function, and N2 elimination, Undersea Biomed. Res. 18 (1991) 279-292. regards, David Doolette ddoolett@me*.ad*.ed*.au*
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