From: "Steve Harris" <sbharris@ix.RETICULATEDOBJECTcom.com> Newsgroups: rec.martial-arts,misc.fitness.weights,sci.med Subject: Re: Hyperventilation before a burst of metabolism Date: Sat, 18 May 2002 15:45:19 -0700 Message-ID: <ac6lje$v8d$1@nntp9.atl.mindspring.net> Carey Gregory wrote in message ... >"Richard Cavell" <richardcavell@mail.com> wrote: > >>This thought occurred to me today: >> >>During a burst of energy (such as a fight), most people will use up their >>oxygen reserves pretty quickly. They then run on anaerobic metabolism. >>Arterial pO2 can be artificially raised by breathing oxygen concentrations >>that are higher than that found in air (as in a paramedic supplying oxygen >>by mask), or by hyperventilation. >> >>It occurs to me that oxygen therapy before a burst of metabolism could well >>delay the switch to anaerobic metabolism, and delay an oxygen debt. Has >>anyone tried this? >> >>Surely I'm not the first person to think of this. So why don't Olympic >>swimmers walk out to the blocks with scuba tanks attached to their faces? > >Since someone else has already pointed out that scuba tanks are filled >with air, not oxygen, I'll merely add that the primary effect of >hyperventilating is to blow off CO2. It doesn't raise O2 levels >significantly. There's not much a normal, healthy person can do to >significantly increase their O2 saturation. Even breathing pure O2 >has a minimal effect. That's true when resting, but it may not be true if you've got a severe V'/Q' mismatch. Also, you can always raise your SpO2 a little with pure O2 breathing, as even normal lungs have bit of "physiologic" shunt. At sea level you'll see you SpO2 go from 94% or so in a young person to 99. If you've hit your anaerobic threshold it can be for a number of reasons, and one of them can be that you've hit O2 delivery limits due to inability to let your venous sats (which you never see with a pulse oxymeter) fall any further and still extract O2. You can up that a bit by O2 breathing to slightly increase your arterial content, and thus delivery, even if your arterial Sats are good on air and your shunt is no worse than normal. You don't affect it much, but 5% can be felt. You can see this effect on endurance sports at even medium altitudes (like 4000 feet) even though these aren't enough to affect resting SpO2 much in a healthy person. BTW, if you'll pardon the personal subjective observation-- scuba tanks aren't always filled with air, even for shallow sport diving. In fact I typically dive EAN ("nitrox") when I can get it (which is most of the time), and that's anything from 32 to 40% oxygen (this helps a bit on nitrogen loading so you can stay at moderate depths like 70 ft for longer, without needing decompression stops). It happens not untypically that after a dive I have to do heavy ocean swimming against current or through kelp beds to get back to a dive boat, and I can tell you that it certainly feels easier to do breathing 40% O2 from my reg and tank, than it does air through a snorkel. So much that I've given up even taking a snorkel. And this is at sea level (exactly!) where I'm sure my sats are fine on air. Of course, the endurance difference is subjective and certainly not double blind. Still, I believe I can tell the difference between air and nitrox on surface swims. (Divers typically surface with enough reserve gas for half an hour of surface swimming). I once did a shallow dive on a tank of 50% oxygen which I'd gotten by mistake from boat O2 fill error. Swimming back after that one, I felt like Mark Spitz. It was only later that I put two and two together. For the Olympics there's no way anything you could put in a 40 lb pressure tank would increase an elite athlete's swimming capability enough to compensate for that much extra weight and drag-- even if it was legal under Olympic rules, which I can hardly imagine it would be. SBH -- I welcome email from any being clever enough to fix my address. It's open book. A prize to the first spambot that passes my Turing test. From: "Steve Harris" <sbharris@ix.RETICULATEDOBJECTcom.com> Newsgroups: rec.martial-arts,misc.fitness.weights,sci.med Subject: Re: Hyperventilation before a burst of metabolism Date: Sat, 18 May 2002 17:04:30 -0700 Message-ID: <ac6q7s$2ap$1@slb3.atl.mindspring.net> Carey Gregory wrote in message <59qdeush1pmm8cdb7p86for9b39bs9dpbc@4ax.com>... >"Steve Harris" <sbharris@ix.RETICULATEDOBJECTcom.com> wrote: > >>That's true when resting, but it may not be true if you've got a severe >>V'/Q' mismatch. > >And how many "normal, healthy" people do you suppose have such a >severe mismatch? ;-) That was phrased badly. Even if you're healthy and young you can go from 94 to 99% at rest on O2. And on exersize you may run less than 94% since that normal shunt will be giving you badly desaturated venous blood (50% or even less). Finally, the normal physiologic shunt and your A-a gradient all increase with age. So those "master's class" olympians will get more from the enriched O2 than the younger athletes. Gee, now that I think about it, I got so much kick from 50% nitrox that I ought to do some oxymetry on myself after heavy exercise to see if *I'm* desaturating on exertion ;( I know I'm fine at rest, but maybe I have some PAH or a small PE or something nasty that I haven't picked up. I really could be in much better shape for my age-- it's not like I routinely run marathons-- so I have lots of room to hide a little pathology. SBH -- I welcome email from any being clever enough to fix my address. It's open book. A prize to the first spambot that passes my Turing test. From: "Steve Harris" <sbharris@ix.RETICULATEDOBJECTcom.com> Newsgroups: sci.med Subject: Re: Hyperventilation before a burst of metabolism Date: Mon, 20 May 2002 17:04:32 -0700 Message-ID: <acc2vu$84m$1@slb0.atl.mindspring.net> Carey Gregory wrote in message ...>[headers trimmed] > >"Steve Harris" <sbharris@ix.RETICULATEDOBJECTcom.com> wrote: > >>Deco tanks are filled with pure O2 for open-circuit tech divers who need to >>do long decompressions. These guys stay for hours sometimes, stuck at 20 >>feet, breathing pure O2 with occasional "air breaks" which helps the >>pulmonary toxicity. > >What's the purpose of the pure O2? Merely to provide gas which has no inert gas component. This maximizes the gradient of partial pressure (pp) of inert gas disolved in tissues, with respect to the pp of inert gas in the blood plasma/lungs. That gradient determines how fast dissolved inert gas will move from "slow" tissues to blood/lungs, and be eliminated. The partial pressure of oxygen in the tissues does not act to form bubbles, even when total ambient pressure is much lower than pO2, because oxygen disappears from solution (and presumably from bubbles) from metabolism so quickly that it can't build up. By contrast, inert gases like helium and nitrogen are at risk for bubble formation and fizz whenever you drop ambient pressure to less than about 1.3 atm lower than the total pp of all inert gases dissolved in the "slow" body compartment at worst risk (say, your spinal cord). In other words, since it's (tissue inert gas pp minus lung inert gas pp) that drives the process that decompresses you, but it's a max limit on (tissue inert pp minus total lung gas pressure/ambient pressure) that sets the "bends-risk" or DCI limit, you obviously want to keep the lung partial pressure of O2 as high as you can. Alas, that also is subject to a constraint, since there's a limit to how long you can breathe pure O2 at high pressure, without ox-tox and seizure risk. It took J.S. Haldane in historic experiments only a few minutes to go into full seizure, at 7 atm O2 (he was in a pressure chamber so he didn't drown, but a diver well might). You can do a few hours at 1.45 atm O2 absolute, and on decompression people generally go to 1.6, which corresponds with pure O2 breathing at around 15 to 20 feet depth (33 ft = 1 atm in the ocean). Deeper stops, however, cannot be done on oxygen, and have to be done on a mix which is less than 100% O2, but they're generally short and decompression divers generally do all of them on the same nitrox mix once they get to a depth which will keep their pO2 < 1.5. It's that last 16 ft rise from 1.5 atm to 1 atm which exposes a diver to most of the decompression risk, and that's why the most decompression time is always spent relatively shallow, at this depth. So the techie divers stay there until their calculations show their risky body compartments are down to no more than 1.3 atm of helium+nitrogen. That happens the fastest when they are breathing pure O2. Not even all tech divers use the stuff, however, since it means an extra dedicated tank full of a gas that can ONLY be used at depths less than 20 feet, and is very dangerous below that. So a much more common deco mix is 50% nitrox, which gives something that can be used down to 70 feet or so, and even deeper in emergencies. Another practical cutoff in scuba occurs for mixes which contain no more than 2200 psi O2 absolute in the tank, which corresponds to 2200/3500 = 63% 02 in the standard high pressure steel 3500 psi scuba tank (we Americans only go to 3500-- in Europe they typically run to 4400 psi or 300 bar). The American Compressed Gas Association does not certify a lot of fittings and components for oxygen at pressures over 2200 psi absolute partial pressure (what you see in your average medical H cylinder of O2) and neither do most scuba shops. So 60% nitrox is all you can get, most places. Tech divers who use 100% O2 are (needless to say) extraordinarily careful with it. Breathing your 50% nitrox by mistake at 100 ft while make an ascent won't do you in, but making a mistake and breathing your 100% O2 at that depth would kill most people by seizure/drowning, in a few minutes. SBH -- I welcome email from any being clever enough to fix my address. It's open book. A prize to the first spambot that passes my Turing test. |
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