Hyperventilation

[trux]

Originally Posted by TRITON

So the conclusion...one can hypervetilate and have more "comfortable" dives but risk BO and all other dangers linked to it,or on the other side less comfortable dives with early contractions and strong DR and therefore better results.

Yes, that is basically correct, though the reality is little bit more complex.

The influence of hyperventilation on diving response is well documented even by the study "Effects of training on forced submersion responses in harbor seals". The study compares "naive" (natural) and "trained" (forced) dives of harbor seals. There was remarkable hyperventilation at the trained dives, and the results well demonstrate the different level of diving response between the naive and trained (hyperventilated) dives.

Now, the conclusion of the study is little bit misleading, because the scientist considers the trained dives being somehow "better" since the oxygenation of muscles is faster, but he ignores that for maximal performances such faster oxygenation is actually a limiting factor, and that the "naive" dives with stronger diving response would allow the seal much longer apneas.

[Fondueset]

One of the best threads ever. Eric and Trux - hope you guys keep at it.

[trux]

On the other hand, in the sake of maximal objectivity, I must admit I found also some documents claiming that seals do hyperventilate. For example this document "Physiological control of diving behaviour in the Weddell seal Leptonychotes weddelli: a model based on cardiorespiratory control theory" includes such claims.

It is not quite clear though whether the results, assumptions, and conclusions in that document are based on real observations, or if they are only the results of their purely theoretic simulation model. Both empiric and simulated data appear to be mixed there, and after reading quickly through it, I do not yet have quite clear picture. I'll need to study it (and the quoted sources) better. Anyway, it looks that even the author admits, the model is simplified: "It must be acknowledged, however, that the cardiovascular control system is far more complex than this simple model implies".

If I understand the text well, it looks like that their assumptions about hyperventilation come principally from the study by Kooyman et al. (1971) (that I did not see yet). In that study seals were observed with post-dive ventilations up to eleven-fold (225 l/min) of the resting volume (20 l/min). Personally, I do not think it necessarily means hyperventilation - it is normal that the ventilation after a dive is above normal. It still is not any hyperventilation, unless it is prolonged even after the levels of CO2 and O2 normalize. From the text it is not immediately clear to me if they really detected pre-dive hyperventilation accompanied with significant hypocapnia at seals. I'll have to dig into it deeper.

EDIT: unfortunately the Kooyman studies are not available freely, and I currently cannot afford spending too much money, so starting to pay for all the documents that I'd like to read (I'd need thousands of dollars) is not an option. However, I'll list the links for those who have academic access to scientific libraries, who can then study them and post their impressions:

http://www.sciencedirect.com/science...&_urlVersion=0
http://www.sciencedirect.com/science...&_urlVersion=0
THE PHYSIOLOGICAL BASIS OF DIVING TO DEPTH: Birds and Mammals - Annual Review of Physiology, 60(1):19 - Abstract
(and of course, there are many more listed at the bottom of the study listed at the beginning of this post)

[hteas]

Eric and Trux,
one of the activities that hasn't been discussed is the transfer of O2 from the lungs to the mitochondria, where it is used in respiration. Hemoglobin has a high affinity for O2. As it reaches the extremities the pH drops, due to metabolism. As pH drops, the affinity for O2 drops as well, liberating oxygen. The oxygen is then transferred (somehow) to the myoglobin in the cells, where it awaits respiration in the mitochondria.
This affects the discussion in the following way. As pH drops, the oxygen tends to be set free, where it can be scavenged and moved to the myoglobin. When hyperveltilating, pH rises, increasing the affinity of hemoblobin for O2. So, when hyperventilating you are likely to keep the O2 attached to the hemoglobin. This may be the reason for increased O2 in venous blood noted by Eric. The net effect on a freediver, is unclear to me, however. : 0
My suggestion is that we learn to increase our cellular myoglobin stores, and act more like marine mammals instead of terrestrial ones. How to do that remains a mystery so far, but I doubt it is totally impossible.

What do you guys think?

Eric: did you hyperveltilate before your recent -67m dive at the blue hole?

Howard

[trux]

Originally Posted by hteas

Eric and Trux,
one of the activities that hasn't been discussed is the transfer of O2 from the lungs to the mitochondria, where it is used in respiration.

You probably did not see post #40

[hteas]

Sorry Trux, you are right. I missed it this morning.
But, I still think that it is important. During hyperventilation the O2 transfer does decrease, but is not eliminated. CO2 is way down, even in peripheral tissues, and there is plenty of O2 in the blood.
The other thing is myoglobin restoration in the cells. Doing a long, slow breathe up will allow the myoglobin to be recharged maximally before hyperveltilation starts. This might maximize both recharged O2 and low CO2 at the strt of a dive.
All of this for me is guesswork. I was originally trained by Annabel Briseno to take 3 "cleansing breaths" and then go. Yes it was hyperventilations, but not a high number of them, and with a stated goal of fully filling the alveoli with O2 saturated air at the start of the dive, rather than minimizing toward CO2. I've never experimented with serious classic hyperventilation (deep and fast, or worse, just fast)
Howard

[trux]

As I explained in the post #40, you do not really want low CO2 and higher O2 affinity to hemoglobin, because it makes the discharging of oxygen in cells more difficult and may help creating certain level of oxygen debt before you start the apnea. So although you saturate a smaller part of the the venous blood better than with normal ventilation, the higher oxygen affinity may backfire on you, eliminating so the advantage at least partially.

Also do not forget that the low CO2 will cause vasoconstriction in some parts (most importantly the brain), where the saturation will then drop considerably. In the sum, the gain of the initial oxygen volume is really not as massive as it may seem.

The only way I see to improve the venous saturation without lowering your CO2, is definitely not slow deep breathing or "cleansing breaths", but increasing the blood flow - high heart-rate and vasodilatation (without physical effort). As already written, stress, or fear may work well.

Cleansing breaths, purging, slow deep breathing, fast breathing, ... - that's all still nothing else than hyperventilation leading to hypocapnia and all its consequences mention earlier in this thread. And yes, I admit it has some advantages too, but the list of disadvantages simply seems to be longer and more important.

[hteas]

Trux,
Visualize a very slow, quiet, gentle breathe up for several minutes to minimize O2 debt and maximize myoglobin loading. Then 3 quick hyperventilations and go. The drop in O2 to the brain (maybe the source of surface sambas) should be temporary as the diving reflex kicks in, dramatically increasing blood flow (and blood pressure) to the brain. As CO2 builds, O2 becomes more availabe for the muscles during the dive.
Irealize that this flows against FRC as well as a lot of training. I'm just wondering about maximizing the dive, especially for recreational diving or spearfishing, not pure apnea.
Howard

[trux]

And additionally, you are also not really right with the myoglobin. Paradoxically, in contrary to what you would assume, the hyperventilation may deprive you of the stores of available myoglobin. The following document studies myoglobin oxygenation in inactive forearm muscles of hyperventilating cycling subjects (hence some muscles are working). It is not perfectly matching a completely inactive/resting hyperventilating freediver, but it demonstrates that there indeed is a direct conflict between recharging the myoglobin and hyperventilation.

Relationship between Oxygenation in Inactive Biceps Brachii Muscle and Hyperventilation during Leg Cycling

From the summary: "Thus, we concluded that decrease in oxygenation in inactive arm muscle is closely coupled with increase in the amount of hyperventilation."

So that adds another serious minus point to the already pretty long list of disatvantages of hyperventilation (or purge/cleansing breaths if you prefer calling it so)

Also this following document concludes that "O2 delivery was impaired in the hyperventilation condition"

Effects of hyperventilation on phosphocreatine kinetics and muscle deoxygenation during moderate-intensity plantar flexion exercise -- Forbes et al. 102 (4): 1565 -- Journal of Applied Physiology

And you will find also other documents addressing this issue

[trux]

Originally Posted by hteas

Visualize a very slow, quiet, gentle breathe up for several minutes to minimize O2 debt and maximize myoglobin loading. Then 3 quick hyperventilations and go.

I am persuaded that it is still wrong and counterproductive, Howard. Of course, it works too, but on my mind, letting the body taking care of the ventilation and oxygenation alone, without trying to control the breath, is the best thing you can do. It is surprising, but our own brain outsmarts us almost always, because it is able to care about us better than we can do ourselves

[hteas]

Trux,
I like that last! Thanks
Howard

[chrismar]

Originally Posted by hteas

Trux,
Visualize a very slow, quiet, gentle breathe up for several minutes to minimize O2 debt and maximize myoglobin loading. Then 3 quick hyperventilations and go. The drop in O2 to the brain (maybe the source of surface sambas) should be temporary as the diving reflex kicks in, dramatically increasing blood flow (and blood pressure) to the brain. As CO2 builds, O2 becomes more availabe for the muscles during the dive.
Irealize that this flows against FRC as well as a lot of training. I'm just wondering about maximizing the dive, especially for recreational diving or spearfishing, not pure apnea.
Howard

Funnily enough, that's quite similar to what was suggested in the 2006 DAN Workshop on Breath-Hold Diving.

Originally Posted by DAN Workshop

The effects of hyperventilation start with the
first few breaths. You increase the oxygen scores, alveolar PO2 from 120 to 130 mmHg on the first
few deep breaths while actually having minimal effect on CO2 elimination.

[wes]

I have done the begginer (with Martin as only instructor), intermediate and advanced with (Kirk, Mandy and Martin) and advanced PFI course (with Kirk and Mandy) as well as a dozen training days with Kirk and Mandy and would say they teach a range of breathing techniques and breathing patterns so that students lean how to manage their CO2. These techniques for sure include purge breaths and how by doing sequential purge breaths you can lower your CO2. They also have students experiment doing holds with no purge breaths, and the point, I believe, is not to teach a "correct" way to do anything, it is, in my opinion, to teach the student different ways to approach freediving and the affects these different ways have.

As for myself I do more intricate warm ups for static including purge breaths and for pool dynamic do a "no warm up" technique with no purge breaths which has worked very well for me. The last time I did a competition as I was waiting and breathing "normally" I noticed a light headed feeling so for sure was lowering my CO2 even though I was trying to breathe relaxed and slow and naturally. So when I felt light headed I immediately stopped breathing for about 30 seconds untill it fully went away then breathed normally and about 60 seconds later started my dive.

I also have found that doing repetitive depth dives I need to "hyperventilate" about 1 min after each dive then do "normal" breathing for the remainder of the dive interval, maybe 3-4 more minutes then dive again. If I forget to do the 60 sec hyperventilation after I come up from my dives I will get a uncomfortable headache about 1 hour after diving that lasts 2-3 more hours. I attribute this to CO2 buildup during my dives. I haven't heard of anyone else doing this and I didn't learn this technique at PFI clinics.

The point of all this is to say that as a result of my PFI training I can choose to do "hyperventilation" breathe ups or not and am aware of the feelings and affects these have on my dives.

Cheers Wes

[trux]

Originally Posted by chrismar

You increase the oxygen scores, alveolar PO2 from 120 to 130 mmHg on the first few deep breaths while actually having minimal effect on CO2 elimination.

Yes, I agree, these numbers may sound very impressive - The difference between 120 and 130 is roughly 8%! Who would not want improving his/her PB by 8%!.

The values are misleading, though. The normal atmospheric pressure at sea level is 760 mmHg (the normal O2 partial pressure in dry air is ~21% which equals to the partial pressure of ~160 mmHg, much less in alveoli). So by increasing the alveolar pressure from 120 mmHg to 130 mmHg, it makes 10 mmHg difference, which then represents 1.3%, and is already not as impressive as the 8%.

This 1.3% represents roughly 100 ml of oxygen at lungs of 8 l of total capacity. The nominal resting O2 consumption is 250 ml/min, and 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 think values around 70% - 80% of the original level are more realistic. That vould mean gain of some 5-7 s.

Now, 5 to 12s, even if not a lot, may still sound interesting enough anyway for most freedivers. The problem is that the extra 100 ml of oxygen can come in thanks to washing out 100 ml of CO2. This assumes normal tidal breath-up without any hyperventialtion or deep breathing, and only one single purge breath to achieve the PAO2 of 130 mmHg. In case of multiple purges, or even a moderate hyperventilation, the total volume of removed CO2 will be much higher. The body produces ~200 ml/min of CO2 in rest. It means it will take 30s of apnea to compensate the loss of the single purge breath (considerably more for multiple purges, or a hypocapnic breath-up). And since low CO2 influences the resistance to hypoxemia (P. Lindholm 2002), and brings other disatvantages, the real gain will be likely much lower (if any at all).

Of course, there are many more factors than just those partial pressures and gas levels. We already spoke about most of them here in this thread. As Eric correctly pointed out, there are much more reserves for stocking oxygen in the venous blood. On the other hand, it already requires rather important hyperventilation, that then brings all its disadvantages with it (hypocapnia, shift of Bohr effect, high heart-rate, cerebral hypoxemia, destabilizing neuronal fibers and consequent muscle tension, depletion of myoglobin stores, arterial dilatation and vasoconstriction to certain degree opposite to the one needed by DR, reduced tolerance to hypoxia, later onset of diving response,...)

All that told, I do not claim that there is no way hyperventilation can be used in freediving for improving performances, or for achieving maximal performances. Perhaps yes, but possibly it is very individual, and it may be very depending on diverse conditions. Perhaps some training adaptation helps, perhaps some methods may work better than others. The main risk is that doing the "correct" hyperventilation may not be easily reproducible, and especially when under stress (i.e. competition, or fighting a fish when spearing) it may very easily turn bad.

It is apparent though that hyperventilation has many more disadvantages and trade-offs for its few advantages, than generally acknowledged. For most freedivers, the safety factor is the only argument against hyperventilation. In fact there are many more performance related disatvantages than just the increased safety risk.

[azapa]

Originally Posted by hteas

I was originally trained by Annabel Briseno to take 3 "cleansing breaths" and then go.
Howard

Funny thing Howard, when I first got in the water with the intention of freediving (as opposed to snorkeling around) I buddied up with a local sustenance spearo. These guys have no formal training and to be honest no education (many can't read), but are father to son generations going back thousands of years. He told me: relax for 2 mins, 3 quick full breaths, NOTHING more, then dive. It must have been the Darwinian method that worked best for them.