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Freediving Leading to Sleep Apnea?

Discussion in 'Freediving Science' started by superhornet59, Feb 26, 2009.

  1. superhornet59

    superhornet59 Freediver

    Hey guys, just kind of curious, has there been any studies done to see if freediving related conditioning (ie higher CO2 tolerance) has led to an increased likelihood of developing sleep apnea?

    I've searched a lot of sources but can't find anything. I'm wondering if the fact that your body 'expects' you to hold your breath, and reacts less to apnea than an average joe, can affect your natural breathing cycle, especially during sleep.

  2. chrismar

    chrismar Well-Known Member

    Sleep apnea is primarily caused by obstruction to the airways, or in far fewer cases a neurological imbalance. I very much doubt that freediving would affect or cause either.
  3. superhornet59

    superhornet59 Freediver

    Sorry, I should have been more specific. I'm not referring to the obstructed airway type, but central apnea.

    I understand the mechanism of it is your body not reacting when it should, but rather taking too long.

    Even when we're doing our static times, we don't get contractions until 2 minutes + (for me anyway, and that's without any hyperventilation or breathe up other than a deep breath.)

    Seeing as the urge to breathe is based on CO2 concentrations, whether you take a deep breath or are just taking tidal breaths, the urge for air should theoretically come at around the same concentration of CO2, all other factors aside.

    So, seeing as we take like.. 3-4 times longer than most people (my friends are turning red after 30 or so seconds) to have the same reaction, I'm drawn to ask if our body takes 3-4 times longer to react.. which it obviously does seeing as contractions are involuntary.. but I'm wondering if that mechanism can differentiate between sleep and breath hold, or if we as freedivers genuinely modify our physiology (CO2 tolerance is a physiological characteristic, not just one of those 'its all in your head' things.) in a way that can promote sleep apnea by training the very mechanism that causes it: a body's lack of reaction to hypercapnia.
  4. chrismar

    chrismar Well-Known Member

    Many studies have been done on CO2 tolerance and it's changes over time. These suggest that freedivers DO NOT have noticably higher CO2 tolerance than other people. The adaptions are to do with conserving O2 (which reduces the speed of CO2 production) through relaxation and the MDR. As such, I don't believe that we would have any predisposition to central sleep apnea. My understanding of it is that it is a neurological condition (temporary or permanent) that causes the delay. The apnea episodes are interspersed with hypernea periods, which suggest that CO2 tolerance would be irrelavant.

    An interesting question nonetheless and one I haven't heard mooted before.
  5. superhornet59

    superhornet59 Freediver

    Wow, really? To be honest I assumed all along that training for CO2 tolerance was something in the body, not the mind. Kind of like how certain drugs have a lower effectiveness as they are used over time, I assumed one's body would become less reactive to CO2 over time as well. Do you recall any specific sources you read about this from, I'd be interested in reading some of them. How did they explain the decrease in the 'urge to breath' feeling that our training gives us?

    I'm just shocked cause it'd be odd that I've tortured myself with CO2 tables for so long and they've done nothing but waste time and effort...

    If it is indeed not at all physiological then that would basically close the case on whether or not it can affect your natural breathing rhythms.
    Lewis Matthews likes this.
  6. chrismar

    chrismar Well-Known Member

    Apnea.cz should have indexed some of them, have a look there or talk to Trux. There's a degree of debate over the scientific procedure used though, especially in regards to it's applicability to what we do.

    The main advantage of CO2 tables (which I still do, if you're interested) is allowing yourself to relax during the discomfort. I've seen beginners samba (and in one case black out) without hyperventilation, which means that they ended their dives with if not the same, then a very similar amount of CO2 in their bloodstream as I have. The key here is that O2 is burnt with glycogen to create water and CO2. In other words, it doesn't matter if you did a two minute dive or a ten minute one: With the same breathe-up, the amount of CO2 produced is the same if you reach the same level of O2 saturation.

    The mental adaption that we take away from CO2 tables is relaxation. This is pretty key, because on a two minute hold, you're not uncomfortable for very long. On a ten minute hold...
  7. trux

    trux ~~~~~

    Yes, I know at least about one such study, but did not find it right now with the expected keywords. Will have to look it up later. However, the specific study that I am aware of, compared subjects (freedivers of different levels, and non-freedivers) who inhaled air with gradually increased CO2 content. Top freedivers gave up practically exactly at the same point as all others. Well, there are several reasons for it - one of them is the fact that during breath-hold, the concentration of CO2 in lungs does not really rise much above certain threshold. Instead of it it concentrates in body liquids, and starts releasing only once the breathing starts and the CO2 level in lungs drops. So bringing CO2 artificially into lungs has comprehensibly a quite different effect than rising it in the body. From this point the study was flawed, but the results were surprising anyway - one would expect certain physiological or psychical tolerance at the top freedivers anyway.

    Anyway, I read similar claims about limited CO2 tolerance and CO2 buffering also in other documents, so the increased physiological tolerance may indeed be very limited or non-existing. As Chrismar writes, it looks like the training is more about coping with the bad feelings and learning to relax and save oxygen despite them, than about a physiological adaptation.
    Last edited: Feb 27, 2009
  8. erdooom

    erdooom New Member

    one thing that free divers learn for sure is handling low o2 levels, in a clinic i have been to with a guy who was researching this stuff for a few years with both freedivers and "regular" people, and he said that high level freedivers will reach lower o2 levels without blacking out. Also freediviers usually can handle much lower levels of co2 then average goe. Try letting a beginner breath full breaths for a couple of minutes and see what happens. We all hyperventilate to some level. :)
  9. efattah

    efattah Well-Known Member

    A trained freediver can handle very low levels of CO2 (i.e. hyperventilate without fainting), as well as handle high levels of CO2 (>10% in some cases).

    Personally, I used my oximeter to check to see if I had sleep apnea, and I did !

    I set the alarm to 80% SaO2, and it would wake me up every 5 minutes. I set it for record mode and turned off the alarm. By the morning it had shown that I had desaturated over 50 times, many times to 75% SaO2.
  10. wet

    wet Freediver82 - water borne

    There is overlap of apnea diving and apnea sleep, but I'd guess that most apnea divers do not apnea sleep, and most apnea sleepers do not apnea dive.

    I've looked for, but found no information, on whether other hominids aside from us humans, have sleep apnea, since they (great apes) never dive, and apparently ancestrally did not dive. I'd guess amongst primates, only humans have (vestigial) sleep apnea, which may be pathological in some people but is normal in many others.

    Elephant seals do sleep apnea while ashore and have similar dive apnea while on deep dives; and dolphins, hippos & manatees do sleep apnea underwater AFAIK. I don't know if backfloating sea otters sleep apnea, probably so, giving higher buoyancy.

    I think that hibernating animals in dens and caves also have a form of sleep apnea in association with reduced metabolism, which probably reduces the concentration of CO2 in their enclosed space. Astronauts on the space shuttle need a fan to blow air around, otherwise the CO2 concentrates around their still sleeping bodies.
    Last edited: Feb 28, 2009
  11. superhornet59

    superhornet59 Freediver

    wow! this is all really interesting, thanks everyone!

    I know that yes, we are more adept to low O2 levels and low CO2 levels... when I first started out freediving i used to look like that Japanese freediver from the Big Blue ([ame=http://www.youtube.com/watch?v=7h1SjuY1uqQ&feature=related]YouTube - le grand bleu(version longue) part16[/ame] at like 3:35 onwards for those of you who missed out an haven't seen it yet).. hyperventilating until I was numb. Now, I just do a few purges and go, but even if I do hyperventilate for some reason.. I can't get dizzy no matter how hard I try.

    But seriously though.. I know we've trained mentally, but I really thought we had some kind of higher CO2 tolerance.. very interesting! By the way thanks for the info Wet, I had no idea marine mammals suffered from sleep apnea

    Despite the fact that I was starting to completely agree that it has no connection.. that really is a pretty strange!

  12. wet

    wet Freediver82 - water borne

    That's what I would have expected, that inhaling high CO2 will affect everyone the same, probably the same for marine mammals.

    Reducing CO2 production rate is the difference, I think, by slowing oxygen burning. In normal aerobic breathing (on dry ground), we exhale almost as much O2 as we inhale. In MDR apnea diving the efficiency of respiration improves (we use more O2 from available air), but the sensitivity to CO2 does not change (thank goodness!).
  13. Bill

    Bill Baron of Breathold Supporter

    .....a little off topic but,
    has anyone found any evidence that links apnea and depression?
  14. trux

    trux ~~~~~

    I remember there was already a thread on this topic. Hold on, I'll try to find it.
  15. trux

    trux ~~~~~

  16. trux

    trux ~~~~~

    Yes, I agree as for physiological effects or tolerance, but would expect that freedivers who are used to suffer long minutes in relatively severe discomfort, or even under pain caused by the high CO2, would be psychically stronger, and last at least a small little bit longer than a test object who can't even hold his breath for 30s without panicking. But the threshold that both groups described as unbearable, was practically identical.

    I already mentioned one of the reasons above (most CO2 during apnea is in the blood, not in the lungs), but still I'd expect a little bit more resistance against the effect of CO2 in lungs too.
    Last edited: Mar 1, 2009
  17. wet

    wet Freediver82 - water borne

    I don't know why you would think that. Those that have high CO2 tolerance and poor sensitivity to CO2 would be risky freedivers, because they would never know when to surface and exhale. The solution isn't the increased tolerance to CO2, nor initial hyperventilating to remove CO2, but rather the decreased metabolism and associated reduced oxygen consumption/CO2 production, that allows longer and more continuous dives. Newborns can "apnea dive" for a while without trained CO2 tolerance, simply because they have no aerobic habit of shallow breathing. Adult freedivers long habituated to constant aerobic breathing (high O2 consumption/high CO2 production) must readjust to be 'non-habitual aerobic breather' with MDR while submerged.
    Last edited: Mar 1, 2009
  18. trux

    trux ~~~~~

    Why? Simple - because a top freediver, despite better O2 consumption and CO2 generation, is capable to cope with high levels of CO2 and bear with quite high CO2 levels. He/she is able to withstand the pain throughout until LMC or blackout. Top freedivers do not really rely on CO2 induced symptoms for aborting their breath-hold. They wouldn't be able to achieve a third of the time or distance if they aborted the breath-hold when they feel the first signs of CO2 induced discomfort. Sportive freedivers learn to recognize symptoms of impending hypoxia instead. Of course the CO2 symptoms are still important, but are so heavily influenced by different aspects (diet, breath-up, physical and psychical condition, ...) that relying on them at maximal attempts is simply not sufficient.

    So while an experienced freediver is able to withstand many minutes of CO2 induced discomfort and strong pain, a non-freediver chickens out after the first few seconds of the slightest hypercapnic symptoms. And do not tell me that the CO2/O2 management at top freedivers is so good that after 10 minutes of apnea they have the same level of CO2 as a non-freediver after 30 seconds! :)

    So yes, as I wrote already two times, the limited resistance to inhaled CO2 is partially explainable by the slowly climbing PaCO2 (alveolar partial pressure of CO2) after certain threshold, and also by different processes during apnea, and during normal breathing. But despite it, the result of practically no tolerance difference was surprising. Perhaps not so much for the lapse of physiological CO2 adaptation, but definitely it was surprising for the lapse of mental tolerance difference. And it was not only surprising to common freedivers without deeper knowledge of physiology, but it was surprising to the scientist studying the phenomena too.
    Last edited: Mar 1, 2009
  19. wet

    wet Freediver82 - water borne

    I guess we are speaking of two different things:
    CO2 awareness
    pain tolerance

    As for that study, IMO it is confusing because freedivers don't inhale CO2 but do submerge vertically. I usually don't unquestionably accept study results that are done in the lab, there is too much difference to forage diving, especially cyclical forage diving on sunlit tropical lagoons. Sitting in a swimming pool or bary chamber or in a chair with a hand or head in a icewater bucket can only give partial data, same with computer modeling. The studies are important, but differ from reality in significant ways.

    A cyclical forage freediver is producing minimum CO2 while at depth, except eg. during emergency (shark). At no point is the diver inhaling abnormally CO2 rich air or O2 rich air. The diver is very aware of high CO2 level, and ascends. Unlike a sports diver or spearo, the forage diver does not gain from staying down much longer (and becoming physiologically stressed with calorie costly metabolic reaction), since the prey are immobile sessile benthic shellfish, not fast swimming fish that may be gone by the next descent.

    I think benthivorous sea otters and walruses typically have relatively short dives.
    Last edited: Mar 1, 2009
  20. trux

    trux ~~~~~

    Yes, I already wrote in my original post that the study was flawed from this point of view. Nevertheless, the complete lack of difference in mental ability to withstand the induced pain was still surprising. That was the entire point of my comment. And it does still surprise me, despite that I understand the difference to real diving, and that I understand that physiologically the function of CO2 remains the same.