They said in one of the papers that medically induced hypocapnia decreases blood flow to the brain by 7%. However, the blood is more oxygenated. Not clear how they can claim the tissue is being starved of oxygen by those numbers. It's worth pointing out that people are laying down or sitting when they are doing this breath work and so in a state with minimal need of oxygen.
Hey there Levels,
I think there could be several complicating factors regarding the brain's cerebral blood flow and
utilization of oxygen, and the downstream consequences of disruption of those systems and pH alterations.
The first thing that should probably be discussed is
Bohr's Effect, wherein carbon dioxide essentially helps the tissues
utilize oxygen (we shall note the difference here between saturated blood oxygen levels and tissue
utilization of oxygen, the latter of which is increased by having some carbon dioxide present).
The second complicating factor to note is that the downstream consequences of ischemia have largely to do with disruption of active ion pumps like the ATP dependent sodium-potassium pump. A main cause of cell death in stroke is not directly due to the ischemia but rather due to the failure of such pumps as they are deprived of energy (some of these pumps can use up more than 50% of a neurons energy).
As the pumps fail, the neuron's excitability increases and downstream neurotransmitter release is increased - a lot of the cell death in stroke is actually due to excitotoxicity from excess release of excitatory transmitters such as glutamate. Some of these pumps are known to be
pH sensitive as well. My guess is that the effects of this breathing technique have to due with alterations in function of these ion pumps, for example resulting in glutamate release in cortex.
The antidepressant effects of ketamine are seemingly thought to be largely due to glutamate release in cortex, but there are some safety concerns there as well. Specifically regarding a set of neurons known as parvalbumin positive GABA interneurons - these neurons are particularly sensitive to excitotoxicity and there can also be dysfunction induced by glutamate that isn't limited to excitotoxicity.
Ketamine seems to be able to reduce these neuron's expression of parvalbumin and GAD67 (an enzyme that helps the neurons synthesize GABA) and while this seems to play some role in ketamine's antidepressant effects, it can also play a role in its psychotomimetic effects (parvalbumin/GAD67 expression issues are noted in those with mental illness like schizophrenia as well).
Comparing this to a plastic bag over ones head is a bit alarmist don't you think. Especially since the plastic bag over the head would induce hypercapnia. As for the concentration of oxygen in the blood, it has profound effects on the body. I can hold my breath for over 3 minutes after 2 minutes of Wim hof breathing before experiencing the need to breath. I cannot hold my breath that long without the breath work.
Part of what I meant there is that this seems to be the kind of thing somebody would do to get high when they run out of drugs. If the technique and experiences are therapeutic then there is certainly wiggle room in my opinion. Every therapy modality and drug is different, and this technique must have a unique risk-benefit ratio just like all other therapies. However, I'm pretty quick to point out the risks of all therapy modalities, so I hope it doesn't seem like I have it out for this technique in particular.
Regarding being able to hold your breath much longer after hyperventilation - I think this can be explained without having to invoke some sort of increased oxygenation of brain tissue type explanation. Respiratory drive in particular is a funny thing. Carbon dioxide increases respiratory drive via effects on the brainstem and I suspect that people would be able to hold their breath for much longer during hypocapnia - which I believe you are experiencing regardless of whether you go full-tetany mode or not.
Its possible that hyperventilation related increases in the ability to hold the breath have very little to do with oxygen levels and everything to due with decreased carbon dioxide mediated activation of respiratory drive.