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Scuba Forum / UK Scuba / March 2007Residual Volume of lungs and OOA
Hi guys, I have a query that I thought someone here may be able to help me with. I was in a conversation about lung capacities etc, and my friend was of the opinion that during a free ascent in an out of air situation, the expansion of the residual air in the lungs would cause more O2 to diffuse into the blood and 'buy more time' as it were. I would have thought that this wouldn't happen, as the PO2 in the lungs would decrease on the ascent and perhaps the reverse would happen (i.e. some of the bloods O2 would diffuse into the lungs, further lowering the PO2 in the blood). What would be more likely? Thanks, Eddie > and my friend > was of the opinion that during a free ascent in an out of air > situation, the expansion of the residual air in the lungs would cause > more O2 to diffuse into the blood and 'buy more time' as it were. If you keep the air in your lungs during an ascent you will not be worried about O2. There is no 'designed in' over pressure valve in your lungs and holding your breath will probably kill you. Lung over expansion injuries are probably a more messy way to die than putting up with the discomfort of not breathing. Conversely look at freedivers. The most dangerous part of a freedive is the last 10m of the ascent where the expanding gas in the lungs has exactly the opposite effect as the oxygen partial pressure drops. Sorry. This is a non-starter. Blow bubbles all the way to the surface just like they teach in every agencies diving 101. nigelH > If you keep the air in your lungs during an ascent you will not be worried > about O2. There is no 'designed in' over pressure valve in your lungs and > holding your breath will probably kill you. Depends on how deep you are when you start and how much gas is in the lungs at that point. OOA tends to happen with lungs empty or nearly so. If your lungs start at about 1/4 full, you can ascend from fairly deep without risk of expansion injury. Take it from someone that had to do it, it's a lot better to take advantage of the additional gas you can get from your tanks than to test your ability to ascend holding your breath. > Conversely look at freedivers. The most dangerous part of a freedive is > the last 10m of the ascent where the expanding gas in the lungs has > exactly the opposite effect as the oxygen partial pressure drops. Nigel, my friend, I suspect you know better. Shallow water blackout is not because the gas in the lungs draw O2 from the body. It is because the body uses up the O2 in the tissues to a point that it drops below a PPO2 of .16 during the ascent, leading to unconsciousness. > Sorry. This is a non-starter. Blow bubbles all the way to the surface > just like they teach in every agencies diving 101. Just goes to show how wrong Diving 101 can be. Your statement is true only if you have a complete breathing system shut down. If your regulator is still working and hooked to one or more tanks, you can get a breath or two on the way up, even from a single tank. The more gas in your lungs and the deeper you are, the more important it is to ensure you do not close off your airway, but blowing bubbles is not the only way to do that. It's open when you're breathing in too. Lee > Hi guys, > I have a query that I thought someone here may be able to help me [quoted text clipped - 6 lines] > (i.e. some of the bloods O2 would diffuse into the lungs, further > lowering the PO2 in the blood). What would be more likely? First, in such an ascent you must NEVER hold your breath and in fact breathe out continuously. As you ascend the volume of gas in your lungs would increase so as to pressure-equilibrate with the water surrounding you, which pressure is decreasing all the time. Hold your breath and the pressure in your lungs may well cause an alveolar rupture which would give to a pneumothorax or a gas embolus. Neither is pretty, both are capable of killing you. As you ascend (and take the example of breathing air at 30m) your PiO2 (press. of inspired oxygen) in your lungs would fall from 84kPa (4ATA at 30m) to 21kPa (1ATA at surface, 0m). (Actually they'd be a bit less than this becuase of dilution with nitrogen in your residual lung volume, but this will do for this argument.) There is then no question then of more oxygen diffusing into the circulation as you ascend. However, when breathing 21kPa O2 (as we are when sitting at our PCs) we are able to saturate the haemoglobin in the blood to its maximum capacity, and having higher inhaled oxygen concentrations does not add any more to this. What will happen of course is that the amount of oxygen in solution in your blood will fall, but that part of the oxygen in our blood is a very small part of the total and does not contribute significantly to the amount of oxygen our blood carries. However as you ascend it is the case that there is sufficient oxygen in the mass of gas in your lungs so that you need never become hypoxic during such an ascent, so you need not fear for that. Carbon dioxide is another matter. Your desire to breathe is far far more significantly regulated by the partial pressure of CO2 in the blood than that of oxygen in the blood. Normally you remove CO2 from the circulation by venting it to the atmosphere with each breath. As you ascend, and as you breathe out continuously, CO2 is also being vented continuously as you go so the PaCO2 (pressure of CO2 in the arteries) is NOT NECESSARILY raised either. I say not necessarily because frankly it all depends how well you vent. Under-vent and it builds up a bit. So, you should arrive at the surface in a (gas pressure terms) fit state. Of course you will probably experience a certain amount of shortness of breath, as likely to be brought about by anxiety / fear / panic rather than any alteration of your blood gas profile. There is also the question of the strech receptors within the lungs that frankly like to be kept moving. As you vent and maintain a farily constant lung volume so your lungs do not expand and contract during such an ascent. These receptors fire off, reminding you to breathe. You can see their effect by your PC. Take a breath (NOT a full lung capacity!) and hold it. Just as you get the desire to breathe, while neither breathing in nor out, move your chest wall AS IF breathing - you'll find you can buy yourself a few more seconds of breath hold. Hope this helps. Ken > First, in such an ascent you must NEVER hold your breath and in fact > breathe out continuously. As you ascend the volume of gas in your lungs [quoted text clipped - 3 lines] > to a pneumothorax or a gas embolus. Neither is pretty, both are capable of > killing you. > As you ascend (and take the example of breathing air at 30m) . . . Good depth to discuss. Most divers find out they are OOA when they have breathed out, not when they have a lung full of gas. Without getting into the question of tidal flow and minimum percentage content of the lungs, assume for a second that your lungs are only 1/4 full when you discover you are out of gas at 30 meters. As you note, you are at a absolute pressure of 4 atmospheres. At the surface, the gas in your lungs will have expanded all the way up to, you got it, one lung full of gas. This is not suggesting it's a good idea to hold your breath while ascending. It is only to point out that the degree of risk is not normally as severe as taught. You should never ascend very far with the airways closed, but breathing out is not the only way to keep them open. They're open when you are inhaling too. As you ascend from our proposed 30 meters, the amount of gas available from the tank benefits from the lowering of pressure. From the 30 meter dive to the surface, you can actually get extra gas equal to 3 times the internal volume of your tanks. One ata stays in the tank. The other two can be used. So figure out what the internal volume of your tanks is, multiply it by 3 and divide it by whatever you figure the tidal volume of your lungs is. That's how many additional breaths you get on your way to the surface. Rather than exhale all the way, something you do only if you have absolutely no other option, take advantage of the additional gas and make a successful ascent a lot more likely. > However as you ascend it is the case that there is sufficient oxygen in > the mass of gas in your lungs so that you need never become hypoxic during > such an ascent, so you need not fear for that. That is not something you can depend on. There are too many variables. Shallow water blackout is caused by the combination of O2 used by the body tissues and reduced pressure that combine to bring the PPO2 to less than .16 ATA, the level normally considered necessary to maintain consciousness. Lee >> First, in such an ascent you must NEVER hold your breath and in fact >> breathe out continuously. As you ascend the volume of gas in your lungs [quoted text clipped - 13 lines] > pressure of 4 atmospheres. At the surface, the gas in your lungs will > have expanded all the way up to, you got it, one lung full of gas. Like so many things, it depends. Sure you tend to find out you're out of air when you try to breathe in and can't - so your lungs are at the end of a normal exhalation. At which point, for an adult with a total lung capacity you'll find your actual lung volume is around 3L. This is made up of what you can still forcibly breathe out - your exhalatory reserve volume - plus a certain volume which you CANNOT breathe out, your residual volume (both these together make up your functional residual capacity). If you take 3L and multiply it four-fold (4ATA @ 30m to 1ATA at 0m) you end up with a 12l vol - twice your total lung volume. If you don't exhale AT SOME POINT on your way up, you WILL get a pneumothorax / gas embolus. > This is not suggesting it's a good idea to hold your breath while > ascending. It is only to point out that the degree of risk is not normally [quoted text clipped - 7 lines] > the internal volume of your tanks is, multiply it by 3 and divide it by > whatever you figure the tidal volume of your lungs is. Not really. Your equipment is already malfunctioning (assuming it's not your lack of attention that has put you in this predicament). Note that a well functioning first stage regulates to around 10ATA above ambient pressure, so at 30m you will need around 14ATA in your cylinder to get a breath. Sure, as you come to the surface your equipment will function with lower cylinder pressures, as 10+ambient becomes a smaller number. >> However as you ascend it is the case that there is sufficient oxygen in >> the mass of gas in your lungs so that you need never become hypoxic [quoted text clipped - 5 lines] > .16 ATA, the level normally considered necessary to maintain > consciousness. No, this too depends on your rate of oxygen consumption. Of course an option no-one has discussed is using your alternate air source - and I don't mean your second 2nd stage connected to the same empty cylinder! I mean using a pony. I had a free flow at the bottom of Stoney a few years ago, and I made a normal ascent which took me 8 mins from 32m thanks to my 3L cylinder. There is also the option of a "spare air" bottle (he said ducking as everyone throws blunt objects at me!), or one option which is rarely discussed, breathing from the BCD. If you do this, you can breathe in and out continuously as you ascend - but not enough gas there to do a safety stop, just come up. The composition of the gas there is the same as whatever your cylinder held. You breathe in and out from the hose and yes, you do accumulate some CO2 BUT you'll have probably made the surface BEFORE this becomes a real issue. As you are breathing continuously, your airway is open. As you get nearer the surface, you can exhale through your nose discarding some volume as the vol of the BCD will have increased. You may have also dropped some weights, as getting to the surface is a priority and positive buoyancy is not an issue. Ken >> Good depth to discuss. Most divers find out they are OOA when they have >> breathed out, not when they have a lung full of gas. Without getting [quoted text clipped - 4 lines] >> lungs will have expanded all the way up to, you got it, one lung full of >> gas. > Like so many things, it depends. Sure you tend to find out you're out of > air when you try to breathe in and can't - so your lungs are at the end of [quoted text clipped - 3 lines] > volume - plus a certain volume which you CANNOT breathe out, your residual > volume (both these together make up your functional residual capacity). You'll note that the preceeding discussion quite specifically says "without getting into the question of tidal flow and minimum percentage content of the lungs." It also "assumes" the lungs are 1/4 full. > If you take 3L and multiply it four-fold (4ATA @ 30m to 1ATA at 0m) you > end up with a 12l vol - twice your total lung volume. If you don't exhale > AT SOME POINT on your way up, you WILL get a pneumothorax / gas embolus. >> This is not suggesting it's a good idea to hold your breath while >> ascending. It is only to point out that the degree of risk is not [quoted text clipped - 7 lines] >> out what the internal volume of your tanks is, multiply it by 3 and >> divide it by whatever you figure the tidal volume of your lungs is. > Not really. Yes really. My statements are not assumptions and are not guesses. They are based on actual experience. As it happens, my OOA ascent was from 128 feet, a bit short of 40 meters. I was wearing a single 72 cubic foot tank at the time. > Your equipment is already malfunctioning (assuming it's not your lack of > attention that has put you in this predicament). Out of air means out of air. It does not mean a total malfunction of all available regulators. I'm reasonably certain that, if you were to count the number of OOA situations that resulted from lack of attention, failure to monitor gas, or some combination of circumstances that caused the diver to overstay his supply, you'd find that they exceed, by far, the number or times a complete regulator failure was to blame. > Note that a well functioning first stage regulates to around 10ATA above > ambient pressure, so at 30m you will need around > 14ATA in your cylinder to get a breath. Nope. A well functioning first stage stops flowing at about 10 ATA. It starts flowing at a much lower pressure. > Sure, as you come to the surface your equipment will function with lower > cylinder pressures, as 10+ambient becomes a smaller > number. Right, except for the 10 ATA part. That's exactly what I said. You get to use more of your gas as you ascend. Trust me, if you ever have to use it, as I once did, you'll be very glad we had this conversation. >>> However as you ascend it is the case that there is sufficient oxygen in >>> the mass of gas in your lungs so that you need never become hypoxic >>> during such an ascent, so you need not fear for that. >> That is not something you can depend on. There are too many variables. >> Shallow water blackout is caused by the combination of O2 used by the >> body tissues and reduced pressure that combine to bring the PPO2 to less >> than .16 ATA, the level normally considered necessary to maintain >> consciousness. > No, this too depends on your rate of oxygen consumption. Yes if you mean the rate at which your body consumes oxygen in the tissues, which is what I meant when I said "O2 used by the body tissues." I'm not sure what your "no" refers to. > Of course an option no-one has discussed is using your alternate air > source - and I don't mean your second 2nd stage connected > to the same empty cylinder! Probably because having a redundant gas supply means it's not an OOA situation. Note that's not a criticism, just an observation. It is clearly best not to run out of gas included in your dive plan and second best to have a reduncant supply just in case. If we're going to talk options, they let's include all that are likely: 1. I sometimes wear twin tanks with an isolation manifold. A single regulator failure does not mean I'm out of gas or that I can't access all gas through a regulator working just fine. Even if I were to fail to shut down a free flowing regulator before all available gas has escaped, I still have a working regulator to let me take advantage of expansion to get still more gas from the tank. 2. I don't normally carry a pony, but I do sometimes carry a deco gas suitable for use from a bit over 20 meters to the surface (50% O2). In a real emergency, I would use that supply briefly at still greater depths. Ox tox is a function of both PPO2 and time. I would certainly use it above 20 meters. 3. My gas plan calls for ending the dive while I still have enough gas to get myself and my buddy safely to the surface. I may have run out once. I'm not likely to do so again. > If you do this (Breath from your BCD), you can breathe in and out > continuously as you ascend - but not enough gas there to do a safety stop, > just come up. The composition of the gas there is the same as whatever > your cylinder held. You breathe in and out from the hose and yes, you do > accumulate some CO2 BUT you'll have probably made the surface BEFORE this > becomes a real issue. This method presumes you have significant gas in your BCD. The closer to the end of the dive you are, the less gas you're likely to have there. If you're out of gas, you're as buoyant as you're ever going to be and will have less gas in your BCD than at any other point in your dive. It's better than nothing, but not by much. Lee >>> Good depth to discuss. Most divers find out they are OOA when they have >>> breathed out, not when they have a lung full of gas. Without getting [quoted text clipped - 17 lines] > "without getting into the question of tidal flow and minimum percentage > content of the lungs." It also "assumes" the lungs are 1/4 full. Didn't see that assumption. Inj any case, 1/4 full can mean any number of things. 1/4 of total lung vol? 1/4 of a breath already taken (to be added to the functional residual capacity)? etc etc. > Yes really. My statements are not assumptions and are not guesses. They > are based on actual experience. As it happens, my OOA ascent was from 128 > feet, a bit short of 40 meters. I was wearing a single 72 cubic foot tank > at the time. Well done. My figures are neither asssumptions not guesses either. I have professional involvement on a daily basis with all that is being discussed here! It's my bread and butter. >>> That is not something you can depend on. There are too many variables. >>> Shallow water blackout is caused by the combination of O2 used by the >>> body tissues and reduced pressure that combine to bring the PPO2 to less >>> than .16 ATA, the level normally considered necessary to maintain >>> consciousness. Oh I didn't pick this up yesterday. I take issue with your fig of 0.16ATA required to maintain consciousness, and it's not personal experience of mine, but of millions. The cabin pressure of most commercial aircraft is reduced in flight to 2/3ATA, so the PiO2 drops to 2/3 of 21 = 14kPa, approx 0.14ATA (1ATA = 101.3kPa). I've tried a hypoxic mixture myself (high PiN2, 1ATA) in a circle breathing system made purposely hypoxic (by me!) and I was VERY comfortable at 14kPa. It was not until 8kPa that I began to get symptoms, and at 6kPa was in real trouble. > This method presumes you have significant gas in your BCD. The closer to > the end of the dive you are, the less gas you're likely to have there. If > you're out of gas, you're as buoyant as you're ever going to be and will > have less gas in your BCD than at any other point in your dive. It's > better than nothing, but not by much. Never was the saying " A drowning man will lcutch at a straw" a more apt proverb! Ken > In any case, 1/4 full can mean any number of things. 1/4 of total lung > vol? 1/4 of a breath already taken (to be added to the functional residual > capacity)? etc etc. How about something simple, like 1/4 full? > Oh I didn't pick this up yesterday. I take issue with your fig of 0.16ATA > required to maintain consciousness, and it's not personal experience of > mine, but of millions. Not my number, but the one that I believe is used by a pretty well known group or cave divers. If it's wrong, assuming it's not my mistake, you'll have to convine them. Good luck. They're somewhat resistant to change from the outside. >> This method presumes you have significant gas in your BCD. The closer to >> the end of the dive you are, the less gas you're likely to have there. [quoted text clipped - 4 lines] > Never was the saying " A drowning man will lcutch at a straw" a more apt > proverb! Agreed. Lee >> In any case, 1/4 full can mean any number of things. 1/4 of total lung >> vol? 1/4 of a breath already taken (to be added to the functional [quoted text clipped - 10 lines] > have to convine them. Good luck. They're somewhat resistant to change > from the outside. I have better things to do than bash my head against a brick wall. K > Hi guys, > I have a query that I thought someone here may be able to help me [quoted text clipped - 6 lines] > (i.e. some of the bloods O2 would diffuse into the lungs, further > lowering the PO2 in the blood). What would be more likely? No sense wasting the gas in your wing in a pinch. Breath and re-breath your oral inflator of your LPI on your wing. It's nitrox, and breathing will protect from over-expansion. It'll buy you plenty of time for an ESA. > Hi guys, > I have a query that I thought someone here may be able to help me [quoted text clipped - 8 lines] > Thanks, > Eddie Eddie, you will get a pneumothorax, on a free ascent, if you do not breathe out all the way up. The residual air, using Boyles Law alone, will dohule when you reach a depth of 10 metres from the surface. Judith >> Hi guys, >> I have a query that I thought someone here may be able to help me [quoted text clipped - 14 lines] > > Judith Ye, but the arguement was if he only started with (in this case) a half lungs full, he would be ok if he didn't breathe out at all. (Half lungs at ten metres becomes a lung full at 0M) > judith.le...@googlemail.com wrote: > >> Hi guys, [quoted text clipped - 21 lines] > > - Show quoted text - I see what you mean, then I can't answer his orginal question. Judith > Ye, but the arguement was if he only started with (in this case) a half > lungs full, he would be ok if he didn't breathe out at all. > (Half lungs at ten metres becomes a lung full at 0M) I'm not sure lungs work like that. Even 'fully' exhaled the alveoli don't flatten out so what 'a quarter full' might represent is dubious. A full breath at the surface does not leave me enough volume to even let me clear my ears with a normal scuba mask freediving to 30meters. The big danger is there is nothing in our evolutionary environment that could provide lung over pressure so we have no built in protection against it. You can hold your breath against a pressure that will kill you. If we had an over-pressure valve built in I'd say hang onto everything you've got but as drowning in my own blood is not a prospect I relish I will exhale on any ascent that involved breathing compressed air at depth. Actually you have been breathing raised O2 levels (air at 10m = 0.42bar) so you can go a little bit longer and there are tricks to stave off the discomfort from CO2. I don't think you will gain anything O2 wize by holding a breath on the ascent as the O2 has already been taken when the ppO2 was high and as it falls your lungs might actually take oxygen back from your blood. nigelH  SignaturePosted via a free Usenet account from http://www.teranews.com > I'm not sure lungs work like that. Even 'fully' exhaled the alveoli don't > flatten out so what 'a quarter full' might represent is dubious. Why complicate the words to make things more difficult. 1/4 means 1/4 full whether it's in tha alvioli or in open spaces or wherever. Of course gas can be trapped in the alvioli, but that's a completely separate issue. It's a good reason for ascending slowly, but that's about it. > A full breath at the surface does not leave me enough volume to even let > me > clear my ears with a normal scuba mask freediving to 30meters. You freedive to 30 meters? You're better than I am, or ever was. > I relish I will exhale on any ascent that involved breathing compressed > air at depth. One more time. All that is necessary is for the airway to be open. Breathing in, breathing out, or neither as long as the airway is open, excess pressure will adjust. Lee >> Ye, but the arguement was if he only started with (in this case) a half >> lungs full, he would be ok if he didn't breathe out at all. [quoted text clipped - 4 lines] > breath at the surface does not leave me enough volume to even let me > clear my ears with a normal scuba mask freediving to 30meters. Exactly my point in my discussion with Lee Bell. What do you mean by 1/4 full given that they never empty, and 1/4 full from what point of reference? In any case, suppose your maths is correct - half full at 10m = full at 0m, therefore no need to breathe out. Tell me - how accurate is your "lungfullometer"? Do you want to risk a pneumothorax / gas embolus, or do you fancy doing the safe thing nd just breathe out anyway? Which is the strategy with lower risk? > The big danger is there is nothing in our evolutionary environment that > could provide lung over pressure so we have no built in protection [quoted text clipped - 8 lines] > when the ppO2 was high and as it falls your lungs might actually take > oxygen back from your blood. While diffusion back from the blood to the lungs is a reality, it is a reality of no importance. The haemoglobin dissociation curve is such that no desaturation of haemoglobin will occur, and the only oxygen that will diffuse back from the blood into the gas spaces of the lungs is that oxygen which is in solution in the plasma. The amount of oxygen contained in blood is proportional to the haemoglobin concentration, but roughly speaking on average (as all our haemoglobin concs differ (hopefully!) within the normal range there is no ONE correct figure) 100ml of arterial blood holds 20ml O2 at BTP, of which around 0.3ml is in solution. In other words, 19.7 ml is bound to haemoglobin and will not diffuse back into the air spaces at these pressures. (BTP - analogous to STP, used by human physiologists, Body Temp + Pressure where Body temp = 310K (37ºC) and Press = 1ATA) Ken > "Nigel Hewitt" wrote in message >> I'm not sure lungs work like that. Even 'fully' exhaled the alveoli >> don't flatten out so what 'a quarter full' might represent is [quoted text clipped - 5 lines] > 1/4 full given that they never empty, and 1/4 full from what point of > reference? I think you'll find Lee is deliberately vague on that point. He is not doing maths and he has done it in the water which counts for more than our armchair diving. I agree with him that an open airway is enough but it took me a long time to learn to consciously control the valve in my head that switches neither/mouth/nose/both and I'd hate my life to hang on it. Moving gas, I hum rather than the PADI 'blow bubbles', makes it much more sure to be open. >> don't think you will gain anything O2 wize by holding a breath on >> the ascent as the O2 has already been taken when the ppO2 was high [quoted text clipped - 6 lines] > that will diffuse back from the blood into the gas spaces of the > lungs is that oxygen which is in solution in the plasma. Wooo. Haemoglobin only ever gas transfers with the plasma that surrounds it. As the ppO2 in the lungs drops as you ascent the gas transfer in the Alveoli may reverse and hence haemoglobin also under certain circumstances. There is no magic one way valve, just basic physics, at work here. Consider the Freediver's Samba. This always occurs shallow and I've been grabbed returning from a rather slow 22m dive where I remembered it right to the surface but was then told I sambered as I stated to breath down. nigelH >> "Nigel Hewitt" wrote in message > Wooo. Haemoglobin only ever gas transfers with the plasma that > surrounds it. As the ppO2 in the lungs drops as you ascent the [quoted text clipped - 4 lines] > rather slow 22m dive where I remembered it right to the surface but > was then told I sambered as I stated to breath down. The association of oxygen with Hb and the dissociation of oxygen from Hb are not exactly reversible processes at any PO2. The conditions in the lungs are optimally set for association, and while dissociation can occur with a sufficient pressure gradient under these conditions, the conditions are not as favourable. At the point where the oxygen is required, in organs other than the lungs, the conditions are set for dissociation. Lung tissue is so fine that the cells which make up the alveoli don't need Hb for oxygen delivery, they can get what O2 they need from the inhaled gas. Freediving is a rather extreme example and yes it can and does happen here - but a diver doing a rapid ascent is spending far less time apnoeic than a freediver who has gone down and then meets this problem on the way up. Again, there are no absolutes. of course it CAN happen, just not particularly likely to. Factors which influence here are many and varied - what depth is the ascent happening from? How rapidly is the ascent happening? What is the diver's metabolic rate at this time? What gas mix was the diver breathing when he/she experienced the OOA scenario? What's the diver's Hb concentration? What state is the diver's circulatory system in? How big are the diver's lugns relative to body mass? Did the diver begin the ascent at the end of a normal exhalation, of a normal inhalation, or where in between? Does the diver have any mucus plugs in the lung effectively isolating a number of alveoli from normal ventilation? The only thing we can ALL be agreed on I suspect is that as far as OOA scenarios go, you are far far better off NOT encountering one in the first place (keep an eye on consumption, keep equip in good working order etc). Should you be so unfortunate as to need to do a rapid ascent, do so with an open airway (the method of ensuring this is less important than the fact that the airway is open) and let not haste be your killer - you can ascend more slowly in an OOA situation from 3m than you can from 30m. Don't dive if you have any respiratory problem that may cause air trapping, and there is no absolutely 100% safe way of getting to the surface Polaris-style. Ken >> Ye, but the arguement was if he only started with (in this case) a half >> lungs full, he would be ok if he didn't breathe out at all. [quoted text clipped - 17 lines] > when the ppO2 was high and as it falls your lungs might actually take > oxygen back from your blood. People are usually deaf to the concept (in fact I was excommunicated from Scubaboard for advocating it). If you practice breathing the LPI on your wing, you can exercise the need for your lungs to cycle (CO2 discomfort), rebreathe mix you're wasting and only using around 15% of, per lung cycle. It works great, and relieves a lot of the anxiety of an ESA that comes from lung discomfort. |
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