Hyperventilation

[trux]

Originally Posted by efattah

I would also add that it was Peter Lindholm, an expert in physiology, would explained to me how venous saturation increases dramatically with hyperventilation.

I do believe that the increase of venous saturation is higher than the arterial one (although not as high as your oximeter indicates). I doubt though that it makes any dramatic difference in the total amount of oxygen available to the organism after hyperventilation. And any positive difference is further diminished by the negative effects of hyperventilation (muscle tension, vasodilatation, high heart-rate, possible later onset of diving response)

[azapa]

If two or three hook breaths pressurize the torso and avoid rapid a decrease in saturated O2 after a dive, could they also increase saturated 02 before a dive without affecting CO2 levels?

[trux]

Perhaps telling it more clearly: assuming you are in rest, and with constant heart-rate, the venous oxygen saturation will be high in dilated parts, while low in constricted parts. This is perfectly shown in the above mentioned examples where the venous saturation in brain drops by 10% after hyperventilation, while on your skin it climbs dramatically. You would need to measure the venous O2 saturation in the heart to have little bit better clue, but even that would not really tell you how much more O2 you have in all blood volume of your body. That's because on the place you measure (even in the heart) you indeed get more of the high saturated blood from dilated parts, while there is only little coming from the possibly big volume of desaturated blood from constricted parts (i.e. the head) that flows slower hence not influencing immediately the measured level.

And since the vasoconstriction and vasodilatation are to great degree inverted at hyperventilation vs. diving response, the vasoconstriction kicked in by hyperventilation won't directly morf into the vasoconstriction you need.

[trux]

Originally Posted by azapa

If two or three hook breaths pressurize the torso and avoid rapid a decrease in saturated O2 after a dive, could they also increase saturated 02 before a dive without affecting CO2 levels?

I think not really, because the arterial blood is already practically saturated, and to saturate the venous blood, you need blood throughput higher than normal. So maybe if you managed accelerating your heart rate in the same time, but without physical effort (consuming the oxygen), it might have some effect. Actually packing may have such effect - it creates both increased alveolar pressure and higher heart rate. The problem is that when you pack, you are in fact already in apnea, hence the gain won't be interesting since it is anyway oxygen that you already have and don't get more.

EDIT: stress is a good agent for the saturation - it increases the heart rate, and accelerates blood flow. But it causes hyperventilation too, so we are back where we were. So I'd tell artificial controlled stress. That's finally what FRC experts like Seb Murat (and I believe Eric Fattah too) teach

[TRITON]

Maybe I wasn't precise enough in my previous post....
The "leg burn" i mentioned happens only on max attempts or close to max dives and i'm pretty sure that's DR.

Originally Posted by chrismar

I suspect Triton was referring to the feeling of blood shift coming on. For me it happens at a certain point during a dive (in a static, usually around two and a half minutes) where my arms and legs get hot, start tingling (NOT hypocapnia!) and it feels to me like the blood is leaving. Your response is a good one either way.

[Bill]

Azapa
I think that hook breathing has more to do with blood pressure than O2. One breath is enough to get O2 (like we were taught a long time ago) but if the blood pressure drops, it will take a while to get to the head. Much better to stay awake than to wake up face down.

[ADR]

Trust a pilot to correctly point that out !

Hi Bill...its been a while pal, hope you are well

[hteas]

Trux and EricF - Please keep this up, but maybe on a separate thread. It is straying (sort of), but there are those of us on the edge of our seats trying to keep up (seriously). It really has potential to help a lot of practicing freedivers to increase their times, as well as understanding what's going on inside during the attempt.
Howard

[trux]

Originally Posted by hteas

Trux and EricF - Please keep this up, but maybe on a separate thread. It is straying (sort of), ...

Yes, exactly. I already wrote we are getting a lot off topic with it, but am persuaded that the discussion is interesting not only for us who are involved in it. Although this discussion about hyperventilation is directly coming from the controversial article referenced in the initial post, it indeed deserves an independent thread. I suggested moving it to the Science subforum as soon as it is created (as was already pre-announced by Papa Smurf). Once the new forum is up, we should suggest more such threads (or parts of them, like in this case) to be moved there.

[trux]

Well, I'll continue about the topic of hyperventilation here before I forget some details that just came to my mind, and hope it will be all indeed moved to a separate thread later.

As for the saturation of the venous blood - I just realized that there is also another effect that helps increasing it, not only the higher throughput (through increased heart-rate and vasodilatation in some parts). We all know that when hyperventilating, the CO2 level drops, and the pH climbs. And the pH has an important effect on the way hemoglobin binds oxygen. At high pH (low CO2) it binds it very strongly (hence pulling more of it from lungs and saturating the blood), and oppositely at high CO2 (low pH) it binds it worse, and releases the oxygen easier (it helps oxygenating the cells even at progressing hypoxemia).

Still, alone it would not really help increasing the venous saturation more than the arterial one. And since the arterial saturation is close to maximum already at normal ventilation, only the above mentioned increased throughput could help. But, now the high pH not only helps loading the O2 from lungs to blood, it also makes the discharging more difficult. It means that the blood despite being saturated to the max, is unable to deliver and release the oxygen where it is needed. The consequence then indeed is the increased venous oxygen saturation.

But that's not all! The problem is that despite the high O2 saturation, cells are starved of oxygen above normal, and cumulate oxygen debt. And I do not even speak about the brain or some other parts that are starved even more severely because of vasoconstriction of some arteries, and build so oxygen debt more quickly. And that's of course just another factor playing against hyperventilation in freediving, because although you may manage to increase slightly the O2 content in your blood, the organism is in fact deprived of normal flow of oxygen from blood to cells, and will then need to take it from the blood later during the breath-hold, when the unloading becomes easier with the decreasing pH.

EDIT: the strenght of the effect of the oxygen debt building will depend on the length and level of the hyperventilation. Normally it won't be too serious, because the system is self-balancing, but it may be sufficient to eliminate at least part of the little extra oxygen you managed to get by the hyperventilation. So from this point of view, on my mind, the only real "advantage" of hyperventilation is not really much higher O2, but the lowering of CO2 and the consequent prolongation of the comfort phase of the breath-hold. And you all know why I've put the word advantage into double quotes.

[samdive]

About time we had a discussion about "purging" and "Hyperventilation" - I have heard so many trainers talk about "hyperventilation" as if it was with the devil's way to freedive and then tell all their students to "purge" !!! It's the same bloody thing!! or at least the aim is the same - to off gas CO2..... ADMIT IT please!!

(I don't teach it to beginners... but I do use it myself in a limited way)

[trux]

Well, this is not necessarily only safety related, so I'd personally preferred if Stephan could add the promised Science category, where we could move the recent discussion from the Blaine thread, which has already load of information. Otherwise, there are also many other past threads with excellent information about hyperventilation here on DB, so the best would be really collecting them all and moving to the new category, instead of repeating the same discussion here again.

[Adrian]

Trux - if you experience a space- time warp it's because, A), you have been hyperventilating, or B), I've moved the hyperventilation posts to the Safety Forum.

[trux]

OK, I see it now it seemed to be empty at my previous post. Frankly told, this later discussion about hyperventilation is much more about the efficiency than about safety, so I really would like to see the new category dedicated to physiology and other sciences.

Most freedivers know about the safety risks of hyperventilation. And frankly told for an advanced freediver who is capable of pushing through contractions, the hyperventilation (if done always to the same degree) is of less safety concerns, because he has to rely on hypoxic signals instead of the CO2 induced urge to breath anyway.

So hyperventilation, from the safety point of view is especially dangerous for beginners and intermediate freedivers who do not quite evaluate all their body signals during the apnea. Also at those who dive in variable conditions (i.e. spearfishers) - where the length of breath-up, dives, the physical effort, the temperature, the stress, the focus, and other factors differ greatly during the diving session and hence the level of hypercapnia during the apneas changes greatly - there avoiding hyperventilation may be of much bigger importance from the safety point of view.

The latest discussion was more about the physiological advantages of hyperventilation vs. normal or even subnormal ventilation, and hence about the effect on the global oxygen consumption during the apnea with and without hyperventilation. And from the available facts, it indeed looks like that despite a slightly higher starting oxygen volume after hyperventilation, the total consumption may be higher (or even much higher) than at a dive done without it under profound diving response.

[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.

Originally Posted by trux

OK, I see it now it seemed to be empty at my previous post. Frankly told, this later discussion about hyperventilation is much more about the efficiency than about safety, so I really would like to see the new category dedicated to physiology and other sciences.

Most freedivers know about the safety risks of hyperventilation. And frankly told for an advanced freediver who is capable of pushing through contractions, the hyperventilation (if done always to the same degree) is of less safety concerns, because he has to rely on hypoxic signals instead of the CO2 induced urge to breath anyway.

So hyperventilation, from the safety point of view is especially dangerous for beginners and intermediate freedivers who do not quite evaluate all their body signals during the apnea. Also at those who dive in variable conditions (i.e. spearfishers) - where the length of breath-up, dives, the physical effort, the temperature, the stress, the focus, and other factors differ greatly during the diving session and hence the level of hypercapnia during the apneas changes greatly - there avoiding hyperventilation may be of much bigger importance from the safety point of view.

The latest discussion was more about the physiological advantages of hyperventilation vs. normal or even subnormal ventilation, and hence about the effect on the global oxygen consumption during the apnea with and without hyperventilation. And from the available facts, it indeed looks like that despite a slightly higher starting oxygen volume after hyperventilation, the total consumption may be higher (or even much higher) than at a dive done without it under profound diving response.