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> If this 'blow&go' refers to the 'exhale maximally @ depth prior to > ascent' historically used in submarine escape training (not used any > more), I fail to see how this will produce a large gradient. > Irrespective of the amount of exhalation, the residual gas in lungs > (which will be there irrespective of how forcefully one expires) will > have the ppINERT of the absolute pressure @ wh/ that breath was inhaled > at. > Thus the percieved tisssue sat at the aforementioned depth & the > ppINERT of lungs post 'full exhalation' will be comparable. This > assumes no local airway collapse, a problem of blow & go. "Blow & Go", I think, refered to "blowing" the BC full of air and "going" to the first decompression stop as quickly as possible. > >Yes. By Causing a large gradient(~5ata) to exist between tissue nearly > > >saturated at 260fsw (as all *fast* compartments will be after 25 min) > and > >gas cavities pressurized at the ambient 100 ft stop, you could cause a > > >population of bubble nuclei to start growing. > > According to the Haldenian concept, it takes the t1/2=5 min compartment > 30 minutes to 'sat'. THus no 'fast', or, for that matter, no > compartments are saturated in 25 min @ any depth. Saturation is > intrinsically depth based. That is a compartment saturates for a > certain depth. I presume the implication was not that saturation is > reached faster as depth increases. Why is there any validity to the notion that the "fastest tissue" has a half-time of five minutes? Just because Haldane said so? Methinks blood, for example, would have a MUCH faster half-time. But blood is likely NOT limited by diffusibility of gas molecules; it is probably more limited by how long it takes for the blood to pass through the circulatory system. When they found that straight compartment models got people bent, their solution was to increase the maximum allowable tissue tension in the faster compartments, and decrease the allowable tissue tension in the slow tissues. This meant initial stops were shallower, and shallow stops were longer. I'd bet if they did the reverse (lower tissue tensions for the fast compartments and higher for the slwo compartments), they would have gotten people out of the water with less decompression time, and lower incidence of DCI. Of course it would still be a weak model, because it only looks at dissolved gases. > Obviously the relative supersaturation that will exist upon arrival at > 100 ft (or any shallower depth) from a deeper depth is predicated on > depth & duration of deeper sojourns. But level of supersaturation may NOT be the main determinant of DCI > We have had this discussion with Pyle. I think that ascribing the > value derived from IWR solely to bubble 'crushing' may be an over > simplification. Agreed! > Rapid intervention with high ppO2 appears to be the > principal value of IWR. Double Agreed! > The presumed benefit (depth 30 ft) is > preventing tissue anoxia and contribute to the prevention of further > bubble formation (bubble formation based on offgassing of supersat > tissue is time dependent & continues after surfacing) by assisting in > offgassing - a result that can be achieved by 100% surface O2. Maybe, matbe not. Let's take off our lab coats, put the theorizing on hold for a while, and go out and see what happens in the real world, shall we? > Again the value of IWR from the stndpt of bubble/DCS theory is not > clear. It's only clear from what's actually happening in the real world. > The same result could be obtained by slower ascents. The issue here is > the large body of 'no knowldege'. The Haldenian model is based on the > compartment SSat ratio and its reduction. It treats the body as a set > of independent comparments. As this is not reality, it would be > shortsighted to not consider compartment to compartment transfer of gas > during deco, even gas uptake by slower comparments (that R not yet SSat > to the deco depth) while the faster ones are offgassing. In addition > one has to wonder about diffusion & diffusion limited offgassing. Well said. It would also be shortsighted not to consider the effects of the presences of gas-phase bubbles in the blood and tissues. Aloha, Rich
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