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At 22:14 04.03.98 -0500, Tom wrote wrote: >>Simply, if a fat diver with poor circulayion to slow tissues off gasses >slower >>than a slim diver with better circulation to slow tissues, then didn't the >fat >>diver not on gas as much gas in those tissues in the first place? >Dan wrote: >No, because the highly fit tech diver will be able to run an extremely low >heart rate, with extremely low exertion rate, particularly if they are >scootering, which is always desirable at depth on reefs or in caves. For >this reason, the very fit have the ability to expose a relatively small >volume of blood to gradient, by low heart rate, during the bottom portion of >the dive, and on ascent, can increase heart rate and blood flow by mild >exertion. The obese diver will have less ability to efficiently power his >body at low heart rate levels, and will have no where near the ability to >increase volume of blood pumped through gradient, during ascent and >offgassing. For recreational exposures high fat tissues do not pose deco problems since the slow absorbing tissues have not had time to onload. Post-dive they may actually serve as a sink of high nitrogen solubility and lower the risk for DCS on single dives. However, repetitive dives will be worse since A) the fat diver has retained more inert gas in slow tissues and B) these same tissues may become governing on the second or third dive. In saturation diving obesity is a great liability since then the slow tissues get time to absorb gas to their full capacity. If a technical exposure is enough to load the adipose tissues they'll present a deco problem. A WKPP cave exposure certainly would while say, 30 min at 200' might still be OK. My personal experience (personal in the sense of watching people of different build during hyperbaric exposures) is that gross obesity did not cause more bubbles than in skinny people after air exposures to 170' for 40 min. Upon completed deco everybody was Doppler-monitored and the big guys did not seem to have more problems than the others. Still, an important point is that the truly big divers were never working during the exposure. The whole point is, ultra-slow compartments with a huge dissolving capacity are beneficial sinks when near-empty while they become a great deco problem when they are filled. Since helium is faster than nitrogen a shorter exposure will be needed to get beyond the critical point. Further, as Dan says, when obese divers have to fin hard their workload increases many times that of a fit diver. Since any minor task will mean hard work their ventilation and heart rate are higher. This means faster uptake per unit time than for a fit diver. Now, rec diving probably won't fill the slow compartments anyway. Sat diving will fill them anyway. Thus, single-dive obese rec diving will not reach the critical point and sat diving is always beyond it. A big rec diver will not cross the line while a big sat diver has taken it to the max anyway and may huff and puff all he needs to -- it's already as bad as it can get. Technical diving is in-between. Most exposures are way into decompression, yet far from saturation. If anybody wants to try to do the math, the turning point is where the adipose tissues go into decompression. Remember to count in higher blood turnover from higher work load. regards, Hans -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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