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John, I think my point might be better described by the differences in how much blood (which relates to surface area) can be exposed to a gradient.....the fit diver may realistically pump 40 liters of blood per minute, through the lungs, exposing the blood (through the alveoli) to gradient----which has the equivalent effect of creating MORE surface area in contact with gradient than the unfit diver,......The unfit diver with less than HALF as much surface area in contact with gradient (because they would have less than 20 liters of blood flowing through the alveoli per minute---this equates to less blood surface for exchange to occur in ). The VO2 Max concept, while you are quite correct about it tending to shift body mass toward lower fat levels as it increases (normally this is the easiest way to increase VO2 Max) is conceptually more important in its predictiveness of a high or low volume of recirculating blood flow across the alveoli---blood surface area for exchange to occur.... If you consider this reasoning with the items belowl, you may be more comfortable with the conclusions I am trying to form. Regards, Dan >>Posted on 2 Mar 1996 at 12:16:31 by Dan Volker > >>The concept is, since gas exchange rates vary enormously between ultra fit >>endurance athlete types, normals, and sedentary persons, ingassing and out >>gassing CAN NOT BE PREDICTED ACCURATELY FOR ALL TYPES. > > >I'd like to be the devils advocate here. > >If a sedetary person is well described as far as DCI is >concerned by say a 16 comparment model then it doesn't seem to >matter just how much body mass is in each compartment. > >If you through training for max VO2 can redistribute your >mass (by having little mass in the compartment that models fat >say, and by forcing a large fraction of your muscles into a faster >compartment) you don't seem to have gained as far as DCI is >concerned (in the compartment model) unless you can outright >eliminate compartments which seems mighty hard considering >8% bodyfat is low and there is a slew of muscles not used >in bycycling. > > > >It seems we still need to prove that the increase in >vascular surface area (capillaries) translates into a higher >bulk diffusion rate. The effect could be small but I'd guess >that depends on mean distance to the nearest capillary in >sedetary and active tissue along with probably a slew of other >parameters I'm ignorant of. > > >>..offgassing rates are less tied to straight blood flow and gradient than >>is the ingassing rate. > >Has this been proven ? If yes, I'm forced to agree with your >viewpoints somewhat. > >If the effect is present it seems to me that the muscular tissue >groups are those affected the most. If these tissues are not >the ones limiting the dive (I'm mixing up tissue and compartment >here for the sake of brevity) it might not have major importance >on *this* particular profile. > > >>This same reasoning would predict that in a recreational profile, say 60ft >>for 55min, the unfit diver with poor gas exchange would be less at risk in a >>no -stop ascent to the surface, than would the more heavily saturated fit >>diver....But if both performed 10 minute safety stops, there is no doubt >>that the fit diver would surface with far less nitrogen loading than the >>unfit diver, and we all know EVERYONE should always do a safety stop, anyway. > >I don't like this. *If* your tissue is approximately behaving >like a compartment then both the fit and unfit diver probably >have some tissue in all compartments. Granted you have more >tissue in the faster compartments and thus more total N2 in >your body but this is a separate issue from tissue saturation >levels. > >I'm personally unware of any attempts at linking the total >amount of N2 to DCI risk barring what I've read in your posting. > >I do realize that differences in the rate of offgassing >and ongassing probably could be turned into a form of link >between the two. > >john >-- >Send mail for the `techdiver' mailing list to `techdiver@terra.net'. >Send subscription/archive requests to `techdiver-request@terra.net'. > > Dan Volker SOUTH FLORIDA DIVE JOURNAL "The Internet magazine for Underwater Photography and mpeg Video" http://www.florida.net/scuba/dive 407-683-3592
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