Hyperventilation

[Mullins]

Originally Posted by trux

only part of the oxygen available in lungs can be used, let's assume it is 50%. That would mean we can use 50 extra ml of O2 which could increase the apnea by 12 seconds. And I am not even sure that the alveolar oxygen saturation (exhale air) can drop as deep as 50%.

I was about to bring this up... there is a difference between saying that half the oxygen in the lungs can be used (above) and saying that the transfer of oxygen to the blood stops at a certain pp02 (say half of .21, which is .105).

If you take Trux's statement literally, you could breathe pure O2 and black out with a pp02 of .5. Presumably this is not how it was intended to be read (?) and it is actually the absolute pp02 value that causes you to blackout rather than the proportion of 02 you've used. If this is the case, you would have access to 100% of any extra oxygen you gain from hyperventilation.

[trux]

Originally Posted by efattah

You guys are overcomplicating things. 100ml of O2 equates to about 30 seconds of static time, as you consume about 200ml of O2 per minute during static.

Yes, that's exactly what I claim from the beginning. With the small difference that I use the value 250 ml/min for resting consumption. 200 ml/min is the CO2 production during rest. Those values come from P. Lindberg's thesis. Of course, it may differ at individuals and during the apnea.

As Eric tells, all the percentage values are completely unimportant. I used them solely to get the volume of the extra oxygen from the PAO2 values. The volume difference is the only value that matters. Percentage of pure oxygen increase (8%) are not usable to get the volume, hence I had to use the percentage of the total volume (1.3%) wich was known (8 l).

I stress that all this is strongly simplified, because we are ignoring many other side-effects of hyperventilation (even if it is so short), and the real outcome may differ from this simplified hypothetical calculation.

[trux]

Originally Posted by Mullins

If you take Trux's statement literally, you could breathe pure O2 and black out with a pp02 of .5. Presumably this is not how it was intended to be read (?) and it is actually the absolute pp02 value that causes you to blackout rather than the proportion of 02 you've used. If this is the case, you would have access to 100% of any extra oxygen you gain from hyperventilation.

What I meant is that during apnea you can absorb some oxygen from lungs only to certain level, which is influenced by the gradient between PvO2 (venous oxygen tension) and PAO2 (alveolar oxygen tension), and the affinity of hemoglobin that decreases with the progressing apnea and increasing hypercapnia. With the progressing apnea you can only get some more oxygen from lungs only thanks to dropping venous PO2, which means higher hypoxemia and coming close to blackout. 50% desaturation at the end of apnea is already pretty serious, but the alveolar partial pressure (PAO2) would need to be considerably higher to still allow some diffusion through the alveoli and the intake of oxygen.

It means you can pull only part of the oxygen available in lungs. So yes, you are right, it is more matter of absolute values, than percentage (with pure oxygen in lungs you would use percentually more). The problem with hyperventilation is that the minimal PvO2 also changes.

[seafalcon]

Originally Posted by trux

Where did I suggest that? Quite oppositely, I wrote you have to go out from the atmospheric pressure of 760 mmHg (where the part of the oxygen is 120 resp 130 mmHg). I only told that when forcing inhalation or packing, the total alveolar pressure will be higher (may be more than 20% higher than atmospheric pressure). At higher pressure the alveoli will certainly not collapse.


Exactly. And I also do not do it second time anywhere. I do it only once. I do not want to offend you, but since I do not know about the background you have, and see that you probably do not understand what the total and partial pressures exactly mean, I did the following diagram to demonstrate it:

As you can see, by increasing the oxygen part by 10 mmHg, you blow of CO2, and the difference makes 1,3% of the total of 760 mmHg. You can imagine the rectangles as being the volume of 7.6 liter lungs (10x760ml). The difference of 10 mmHg would then represent 100 ml of pure oxygen (or CO2), which is then 1.3% of the lung volume.

If you still see some double division in the formula, please let me know.


I do not really care from who it comes. I believe the numbers he gives are correct, but they simply do not show any significant advantage. Just the difference of the PAO2 is impressive for someone who does not understand what it really represents, that's all. As you can easily calculate, the effect on the breath-hold is negligible. You'd really need much higher difference of PAO2, or much higher SvO2 (venous oxygen saturation) to get some interesting difference. But as discussed earlier, that already requires more hyperventilation and has many negative side-effects that will eliminate the advantages either partially, or even the negatives totally override the positives.

Hi Trux

I am sure that it is just a number fault but pls if you agree and it is posible to corect the number of co2 at hyperventilated alveolar from 54mmHg to 34mmHg to avoid any misunderstanding in such a serious matter and also for the next that will read this topic.

Tolis

[trux]

Originally Posted by seafalcon

I am sure that it is just a number fault but pls if you agree and it is posible to corect the number of co2 at hyperventilated alveolar from 54mmHg to 34mmHg to avoid any misunderstanding in such a serious matter and also for the next that will read this topic.

Yes, thanks for the heads up, that was an oversight. The rectangle is smaller, the CO2 level is lower, and the PACO2 value should be smaller too. I am going to change the chart. EDIT: it is changed now, so if you reload the page, the image should contain the right value.

[naiad]

Very interesting discussion, not that I understand all of it.

I wonder if the presence/absence of the dive reflex makes a difference? I don't think I have a dive reflex, even without any hyperventilation or breathe-up, and I have never managed the no warm-up no breathe-up method with any success.

[trux]

I do not think it is possible not to have any diving response at all. It may be stronger or weaker; faster or longer to kick in; individual effects may occur with variable intensity; but I do not think it is possible that the body does not react at all.

The question in such case is rather why the diving response at such individual does not occur with expected force. There are external factors (i.e. water temperature), individual predisposition or experience/training (studies show higher diving response at regular freedivers, though it might be also the consequence of natural selection), and physiological aspects having impact on the DR. And one of the most important factors is the CO2 level, and consequent blood pH. So of course, the more you hyperventilate, the lower chance for an early and deep DR. And the lower DR, the less the DR will compensate the negative effects of hyperventilation.

One could tell, if there is no diving response, hence no trade-off between hyperventilation and the DR, then deep hyperventilation would be the best way. However, I believe it is wrong anyway - first, as I wrote, there is always some DR (even if quite weak), and second, some of the negative effects of hyperventilation are so significant that they impact the maximal performance anyway. Most importantly it is probably the decreased hypoxemia tolerance, which then leads to a premature blackout.

When comparing maximal attempts with and without hyperventilation, we have to differ between physiological and psychological maximum. Physiologically taken, as explained earlier in this thread, the theoretical maximum is a trade-off between the advantages and disadvantages of hyperventilation, and also its influence on the DR. But the real performance is more often interrupted because of the psychological barrier, especially if done under high CO2, hence you then do not really compare the maximal physiologically possible times.

Perhaps, in your case, the weak DR is influenced by subconscious hyperventilation even when you think you do not hyperventilate at all. But of course, there may be also other physiological conditions suppressing the DR. Perhaps frequent training in conditions improving the DR (cold water, no thermal protection on extremities, no mask, high CO2, stress, ...) may help waking it up better, and perhaps it will then kick in easier in more comfortable conditions too. Also frequent deep diving may help training the DR - the fact that until recently you only knew the pool and did not dive in open water, may be a reason for the weak DR.

[azapa]

naiad, I agree with trux, it is probably impossible not to have some form of DR.

If you dive in open water try this simple test:
Day 1. Note your given comfort level/dive time on the first dive. Note your maximum dive time for same comfort level in same conditions. It will probably be 3/4 way through your session. (say, in a 2 hour session, your best dives will be at 1:00 to 1:30?)
Day 2. In same depth, water temp, conditions. Enter the water, arrive at dive position and take your mask off, snorkel in, face down and let the cold water flood over your face, let cold water flood into your wetsuit. Keep your face in for at least 5 mins, occasionally "fanning" cold water over it. Then dive. I will bet that first dive will be near your max dive on Day 1 for the same given comfort level. That is some DR factors working for you.

At the beginning, add a dive, say to 10M, and hold on to something until your first contraction, then pop up, and the DR should be enhanced more again.

I was skeptical too, but the above works every time for me.

[Gene_Hobbs]

Sorry I have not been around in a while but while reading the back log I thought it might be worth adding to the reading some:

Lindholm, P and Lundgren, CEG. Alveolar gas composition before and after maximal breath-holds in competitive divers. Undersea Hyperb Med. 2006 Nov-Dec;33(6):463-7. RRR ID: 5053

NW Pollock, RD Vann, ED Thalmann and CE Lundgren. Oxygen-Enhanced Breath-hold Diving, Phase I: Hyperventilation and Carbon Dioxide Elimination. In: EJ Maney, Jr and CH Ellis, Jr (Eds.) The Diving for Science…1997, Proceedings of the American Academy of Underwater Sciences (AAUS), Seventeenth annual Scientific Diving Symposium, Northeastern University, Boston, MA. RRR ID: 4647

Phases 2 through 4 are being written for publication now, we have not had time to get back to it (though I agree, 8 years is excessive). If it takes too much longer, I'll post the grant report we turned in to the Office of Naval Research. Abstract we presented are available though:

Phase II abstract - RRR ID: 648
Phase III not reported
Phase IV abstract - RRR ID's: 6730, 6739


--Please use this link and not links directly to the pdf's in our database, it eats more bandwidth and gets expensive with the traffic we receive lately.

[wjohnson100]

What matters is the % O2 increase over normal useable O2, not the % total volume increase. If the O2 in my lungs increases by 8% then I have 108% of my normal supply of O2 in the lungs. If I can normally deplete about 50% of the O2 in my lungs then my extra 8% would be 16% of my normal useful O2.

The period of time that my lungs effeciently move O2 to my blood increases by 16% too since that is all bonus O2. For most, that time when the SAO2 starts dropping rapidly is in the 3-5 minute range for a corresponding increase of about 30-50 seconds based just on the lung O2 increase alone. Assuming you get a significant venous saturation increase, let's say 10%, for an average increase of 5% for the entire blood supply. Let's also assume you have a 10%/min O2 depletion rate at the end of your holds. That 5% would give you about 30 seconds extra, best case. Your total benefit would be about 1:00-1:20 seconds, best case, except...

Now the negative effects. All that extra breathing introduces significant O2 debt at the beginning of your hold, so let's deduct 45 seconds from the benefit. Lots of CO2 got blown off, so at the end of your hold when you need to be able to consume O2 and your SAO2 is 75%, there is not enough CO2 in your blood at the tissue level to knock the O2 molecules loose from the hemoglobin, so lets give the Bohr effect another 45 seconds for a net loss of 10 seconds. You didn't feel hypoxic symptoms so you continued the dive too long, and at best, failed surface protocol, or at worst, passed out at 10 meters and had to be dragged out of the water by your buddies. Too bad their CPR was rusty. You didn't make it alive to the hospital. The good news is that you felt great until you passed out, so you died happy, and your corpse will have a smile on its face.

So in the end it is probably a wash or a net loss of a few seconds or maybe your life if you hyperventillate. Of course everyone is different.

So where do we go from here? A few purge breaths before a hold to maximize O2 in your lungs might be beneficial in terms of increasing useable O2 in the lungs. If you look at the mathematics of it, 5 purge breaths gets you about all the benefit you can get in that regard, because you will never get 100% new air into your lungs. Sustained hyperventillation has too many risks and negative effects and probably negates the benefit of a few purge breaths. Everyone has to define for themselves the limits of what they are willing to do, so educate yourself and make good decisions. Your life, and the lives of the people who will learn from you, may depend on it.