am running an fMRI study on breath holding

I might have been more appropriate to move the original thread (normally you can do it alone), or asking one of the administrators to do it for you. Cross-posting is an unforutante technique, and leads to spreading of relevant information, complicates references, and researches in the forum. But it is not too bad. Perhaps moderators can still help and merge these two threads together. If not, it is nothing dramatic

As to your questions from the other thread:

[xeno]Julios said:

Am I correct in assuming that part of the purpose of the breathe up is to slowly oxygenate the blood so that the person can endure longer apnea durations?

Click to expand...

Well, this concept is often misunderstood, and hyperventilation is often more than abused. HV can help to increase the oxygenation in three ways:

1. increasing the O2 content in lungs by removing some CO2 - that increase is very minimal, because CO2 is permanetly resuplied from the body, so for removing a tiny fraction of the gas from lungs (getting some more O2 into), you need to remove huge amounts of CO2 from the body with prolonged hyperventilation with all its negative effects
2. oxygenation of the arterial blood - in rest the blood is near to saturated (SaO2 of ~98%). With serious hyperventilation you may achieve perhaps 99% - again a very minimal gain
3. oxygenation of venous blood - due to higher blood trhouput (higher heart rate), and due to stronger Bohr effect (higher binding of O2 to hemoglobin because of hypocapnia), the venous blood may rise quite considerably (up to some ~20%).

So the most interesting is the increase of the oxygenation of venous blood. That has its price, though - it is achieved thanks to strong binding of O2 to hemoglobin at high blood pH. And that again means O2 cannot be easily discharged in the tissue where it is needed, and leads to oxygen deprivation and depleting of oxygen stores in the tissue already prior the breath-hold.

Additionally, such prolonged hyperventilation has then also other negative effects that reduce the final performance instead of helping it: considerably reducing the safe hypoxic tolerance threashold, the effect of hypocapnia on the vasoconstriction, the tachycarida, muscle tension, tetanism (due to removing free calcium), suppressing/delaying involuntary contractions (that normally help cerebral oxygenation), and likely also suppressing/delaying the proper diving response (some studies dispute this effect, but experience tells other).

[xeno]Julios said:

If so, I'm assuming this can be done without hyperventilation.

Click to expand...

I do not really think so. For me the term "breath-up" is a synonymum of hyperventialtion. Some of them lead to a lesser and slower HV, others are equivalent to a very intesive HV. As I wrote, increasing the oxygenation is possible practically mostly in the venous blood, and that is only possible by having higher O2 supply than needed, resulting in stronger Haldane effect (removing CO2 quicker) and stronger Bohr effect (binding O2 stronger, hence depriving cells). And that's exactly the definition of hyperventilation - ventilation over the needs of the body.

So practically any type of commonly used "breath-up" is equivalent to hyperventialtion by definition. And hyperventilation is not only ventilating over your needs, but also ventilating normally, and reducing the needs (i.e. by relaxation). So in fact even plain relaxation while keeping normal ventialtion leads to a certain degree of hyperventialtion.

In a conclusion, practically any preparation to a breath-hold represents a certain level of hyperventilation, but from the perspective of the maximal performance, the less CO2 you remove from the body, the better.

[xeno]Julios said:

If so, what kind of breathe up schedule would you recommend?

Click to expand...

I am usually answering: let your body controlling it, and do not attempt controlling the breating consciously. Your body is smarter than your mind.

[xeno]Julios said:

As for the effects of breath holding on the BOLD signal, there have been a few interesting studies that examine this, so we'll be able to account for these "global" changes.

Click to expand...

Ah, interesting! I am not aware of too many studies in this field yet, so would be interested in the references, if you could provide them. So far, I have in my database at documents medical @ APNEA.cz only a few matches for MRI studies. Although, there may be some more, the direct lookup shows only these two:

BOLD fMRI Identifies Limbic, Paralimbic, and Cerebellar Activation During Air Hunger
Heart rate responses during a breat... [Int J Sports Med. 2005 Jul-Aug] - PubMed - NCBI
So if you know about any others, I'd gladly add them to the library too

Hmmm - probably I am not getting the aim of the experiment but shouldn't the conditions prior to the different breath holds be similar for any results to be valid?

Otherwise if for some holds you start with a much lower CO2 I would expect brain function to be different - it's highly unlikely than any of those taking part will manage to hold until O2 starts dropping significantly.

I would just tell them to breathe normally for all holds and just very the durations of holds ie do a 1 min hold, then maybe 1:20, 1:40, 2 and so on.

Worth bearing in mind that anyone taking part in such an experiment will probably be a bit nervous, so they'll be HV to a certain extend anyway...

Thanks for the references, Julios!

[xeno]Julios said:

If, as you say, hyperventilation ultimately reduces performance, then why do athletes use it when they are attempting static apnea personal bests (or is this assumption false?)

Click to expand...

Yes, hyperventilation ultimately reduces performance through several mechanisms, but I cannot deny that when moderate, it can increase the initial volume of O2 available (although much less then people believe), and that it suppresses the urge to breathe (which is in fact pretty dangerous in a real situation). Freedivers today hyperventilate much less than they used to. That helps getting a bit more O2 while not exhaling too much of CO2. The psychological help of later onset of the urge to breath is then welcome especially at beginners and at less experienced freedivers.

In the same time, I have to admit that a significant part of freedivers still does not properly understand the mechanism of hyperventilation and its consequences. Most freedivers know that hyperventilation is not good, and that it poses a serious safety risk, but that's about all they usually know. Rather rarely I meet a freediver who would know what exactly hyperventilation is. And unfortunately even fewer of them know any further details, such as the impact on the O2 affinity to hemoglobin, Haldane effect, free calcium effect, myoglobin desaturation, carotid constriction, and other details I briefly mentioned above.

Regular DB readers may be an exception, since this topic is discussed frequently here, but anytime I speak to freedivers outside of DB (including some high level athletes and coaches), I am usually shocked how little they know about the physiology. And surprisingly even freediving specific books rarely bring a complete explanation of all effects of hyperventilation.

Trux, Wouldn't the co2 produced by respiring tissues (heart and brain)combined with bradycardia still cause the Bohr shift to work correctly to release the O2 into the tissues whilst not releasing it to minimally respiring tissues? I appreciate that some tissues would get into O2 debt, but would this matter for a few mins?

Eddie, if the basal CO2 level is low, the tissue has to produce more CO2 before O2 is released. It may not be a big problem for muscles and organs you do not use during the performance, but at those you need (incl. the brain), it may play an important role.

Besides other factors that Trux has explained, effect of hyperventilation depends strongly on the ratio of lung volume and body mass. What is allowed for Zeus (Branko Petrovic ) is not allowed for the oxen (99% of other divers).

Erki said:

Besides other factors that Trux has explained, effect of hyperventilation depends strongly on the ratio of lung volume and body mass. What is allowed for Zeus (Branko Petrovic ) is not allowed for the oxen (99% of other divers).

Click to expand...

Do you mean that if you have the lungs (ie O2) for a very long hold, HV then is beneficial? (which makes sense to me, in the same way that when doing O2 holds you need to HV)

No data that it is exactly beneficial, but a short and modest HV has less negative impact to people with huge lungs compared to medium people. They have much O2 in lungs to produce enough CO2 for Bohr shift etc.

Erki said:

No data that it is exactly beneficial, but a short and modest HV has less negative impact to people with huge lungs compared to medium people. They have much O2 in lungs to produce enough CO2 for Bohr shift etc.

Click to expand...

I am afraid it will be just the opposite way. Huge lungs, at the same % of added ventilation will lead to a proportionally more serious hyperventilation and hence to a more important hypocapnia. As I explained previously, you gain very little by replacing CO2 in lungs, so the lung capacity will not help storing considerably more O2. The only part with some considerable increase of O2 is the venous blood, and its volume is independent on the lung capacity.

Huge lungs mean a bigger risk of hyperventilation. Don't forget that already a single deep breath, or a purge is hyperventilation. Moderate hyperventilation, but still hyperventilation. Average person breathes around 12 times per minute a half a litre of air (6l/min). So if a person with 4l lungs does 3 full breaths within a minute (12l/m) it is already 200% of normal ventilation. But if a person with 8l lungs does the same, it would represent 400% hypervenitlation. Double the numbers if they do 6 full breaths per minute.

I do agree, that its easier to get HV with larger lungs, but what I meant was a situation when two divers start apnea with similar CO2 content, then a person with bigger lungs ends with higher hypercarpia. In the extreme situation (huge lungs and very thin body) this could be a limiting factor.

trux said:

Huge lungs mean a bigger risk of hyperventilation.

Click to expand...

No HV risk for me then