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Will, Small molecular weight lipid soluble species, such as dissolved respiratory gases move through the endothelium of capillaries very readily. The mass flow of a molecular species is proportional to the surface of the tissues involved. Remember good old Fick's law from your hemodynamics days? The last time I consulted with my plumber he didn't exactly use the word "moot" or "vascularity", but he did say that pipes in parallel move more liquid than a single conduit. Have you been talking to Richie Pyle again? Best regards, Bill William M. Smithers wrote: > > On Mon, 23 Mar 1998, Bill Mee wrote: > > > The more surface area for gas exchange, the better able for the > > system to transport dissolved gas to the alveolar pulmonary circulation > > and hence the critical level of dissolved inert gas, where bubble > > nucleation occurs, can me minimized. > > > Bill, I'm not arguing about the actual or theoretical benefits > of exercise - I do it because I feel better afterward, but > your argument is the classic perfusion/diffusion discussion. > > And as for bubble nucleation, it has clearly been shown that > in all but explosive DCS cases, bubbles are an a-priori > fact of life, which brings the discussion into the > realm of bubble *management* (read Hills, Yount, Weinke, et. al.). > > But, to the point: > > PERFUSION is simply vascularity, or blood flow rate. DIFFUSION > has to do with classic half-time absorbtions. > > Vascularity, or the rate of perfusion into remote tissues, > is a moot point. > > As I'm sure you know, studies have shown that arterial gas > partial pressures equalize to ambient (alveolar/inspired) > partial pressures in less than one minute. > > This leads us away from discussions of fitness, and into > discussions of average vs. deviant concentrations of > the various half-time tissue volumes for a given individual > (average, or possibly fit vs. unfit), as it becomes clear that > *diffusion* and *bubble management* become more the prevalent > factors than gross perfusion, as you have argued. And while > those factors may be mass/volume per tissue-half-time related, > they clearly do *not* have a correlation to vascularity, > except for the noted fact that people in better cardio-vascular > shape are less likely to be fat-asses, and hence have per-tissue-volume > halftime ratios that more likely reflect the average. > > Granted, this is splitting hairs...a fat fuck is still a fat fuck, > and obviously more likely to get bent... > > Regards, > > -Will > > > A heavily vascularized individual, without a PFO, will move more gas in > > and out of his system per unit time than the sedentary poorly perfused > > one. The Vo2 max test is an indirect indicator of vascularity. > > > > Even so, Captain Zero can be decompressed successfully if he ascends in > > such a differential fashion as to always maintain sub critical levels of > > circulatory gas. Unfortunately, the time and trouble involved make this > > impractical for in water decompression for certain extreme exposure > > dives. This is why the level of injury due to dcs in commercial diving > > is so low. The divers are decompressed very slowly and carefully in > > habitats so that tissue levels of inert gas do not reach levels where > > bubble growth is highly probable. > > > > The answer here is a very simple one. If you want to engage in extreme > > exposure mixed gas diving - and keep the decompression element of risk > > minimal - then you have to pay the price of extreme cardiovascular > > fitness. There is no other way. The requirement here is 5 - 6 days per > > week at no less than one continuous hour per day of intense > > cardiovascular exercise. Forget about about lifting heavy weights. That > > is complete and utter nonsense unless you perform endless repetitions. I > > suggest that some light weight lifting is ok, but don't kid yourself > > into thinking that this is a substitute for real cardio. You must run, > > swim, bike or utilize some type of aerobic conditioning artifice. > > > > Extreme cardiovascular conditioning is the best peremptive measure you > > can take to prevent DCS. Then of course there are turtle bones... > > > > Bill Mee > > > > > > > > Art Ranz wrote: > > > > > > I think the following is what you are referring to. This is the summary of > > > the article. I OCR'd it so the spacing is off, but the text is accurate. > > > Please be careful in reading the last line. It does NOT say that DCS is > > > independent of being fat, it says that conditioning helps the fat pigs too. > > > (so to speak). > > > It also suggests that being immature, male, and castrated helps promote > > > DCS!!!! > > > > > > Art > > > > > > Undersea & Hyperbaric Medicine, Vol. 22, No. 1, 1995 > > > Exercise conditioning reduces the risk of neurologic > > > decompression illness in swine > > > > > > J. R. BROOME, A. J. DUTKA, and G. A. MCNAMEE > > > Naval Medical Research Institute, 8901 Wisconsin Avenue, Bethesda, > > > Maryland 20889-5607; and National > > > Naval Medical Center, 8901 Wisconsin Avenue, Bethesda, Maryland 20889-5088 > > > Broome JR, Dutka AJ, McNamee GA. Exercise conditioning reduces the risk > > > of neurologic > > > decompression illness in swine. Undersea Hyperbaric Med 1995; 22(1):73-85. > > > > > > During development of a pig model of neurologic decompression illness > > > (DCI) we noted that tread-mill-trained pigs seemed less likely to develop > > > DCI than sedentary pigs. The phenomenon was formally investigated. > > > Twenty-four immature, male, castrated, pure-bred Yorkshire swine > > > were conditioned by treadmill running, while 34 control pigs remained > > > sedentary. All pigs > > > (weight 18.75-21.90 kg) were dived on air to 200 feet of seawater (fsw) > > > in a dry chamber. > > > Bottom time was 24 min. Decompression rate was 60 fsw/min. Pigs that > > > developed neurologic > > > DCI were treated by recompression. Pigs without neurologic signs were > > > considered neurologi- > > > cally normal if they ran on the treadmill without gait disturbance at 1 > > > and 24 h postdive. Of the 24 exercise-conditioned pigs, only 10 (41.7%) > > > developed neurologic DCI, compared to > > > 25 of 34 (73.5%) sedentary pigs ~2 = 5 97; P = CO.015). Neither mean > > > carcass density > > > (adiposity) nor mean age were significantly different between groups. No > > > patent foremen ovali was detected at necropsy. An additional control > > > group of 24 pigs was dived to clarify the influence of weight. The > > > results suggest that the risk of neurologic DCI is reduced by > > > physical conditioning, and the effect is independent of differences in age, > > > adiposity, and weight. > > -- > > Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. > > Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. > > -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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