Why do we blackout? Not how, WHY.

[samdive]

Is there a definitive SPO2 range where blackout occurs? I've been playing with a pulse oximeter recently and have only got it down to around 77% - any idea how low it could go before b/o?

 

[Kimmo]

As I mentioned in another thread (as well as Eric earlier) basic SpO2 meters are not quite accurate at lower O2 levels. Also vasoconstriction makes this measuring little hard. Although there are little better ways to measure these values (fex expensive transcutanic systems or straight from the arterial blood), although these systems are quite expensive or needs some special skills and tools.
I have played with these basic SpO2 meters by breathing hypo breathing and succeed getting O2 values somewhere 55%-60% (exhale only CO2 and very little air inside) while keeping these values that low for a while. Unfortunatelly I do not believe in that value while keeping in mind these facts I mentioned earlier.

I have also played little bit with a hypoxicator but that machine makes real hypoxia so I do not recommend it for hard tests

- kimmo

 

[wet]

I was discussing O2, CO2 & gasping for air in the following conversation.
Please help clarify or correct anything, if it's incorrect:

M3D: Breathing remains an involuntary act controlled by the brain that can only be temporarily controlled by voluntary means... In other words we may be able with training, to extend our ability to hold our breath underwater to several minutes.... but there will always be that moment when oxygen
deprivation will force you to breathe (gasp for air), even if the consequence of doing so... is drowning...

DD: Oxygen deprivation never forces O2 intake (gasping), CO2 accumulation forces intake. Drowning may occur for many reasons, but often is due to either:
1) Running out of O2, black-out (more often in divers who hyperventilate
before the dive), no gasp (water may enter lungs but not inhaled)

2) Too much CO2, causes inhaling water gasp (may have plenty O2),
water may enter lungs OR be stopped by glottal valve.

M3D: Gasping seems to be a last ditch, fail-safe...when the body becomes deficient of oxygen."...According to the researchers, during hypoxia, the body shuts down most of the cellular respiratory network and focuses its energy on gasping, which is modulated solely by the sodium-driven pacemaker neurons. If that specific neuron is blocked for whatever reason, the body cannot gasp..."

Neurons that control gasping provide clue to SIDS cause
http://chronicle.uchicago.edu/040715/sids.shtml

DD: Help? This is confusing. Am I missing something? AFAIK, children gasp but infants don't (?)

SIDS = Sudden Infant Death Syndrome, it is reduced by laying infants on their back for sleeping.

DDeden

 

[naiad]

I thought that the cause of gasping and the urge to breathe is mainly high CO2. If I am very hypoxic (BO/LMC, or close to the limit) I take small shallow breaths, less than normal breathing. There is no urge to gasp.

In all the blackouts I have seen or done, there has been no noticeable inhalation of water. Of course the aim is to rescue the person immediately, but there are a few seconds before it is obvious that there is a problem, and it may take a few seconds to get them to the surface. This shows that gasping doesn't happen at the moment of blackout or LMC.

Lucia

 

[wet]

I thought that the cause of gasping and the urge to breathe is mainly high CO2. If I am very hypoxic (BO/LMC, or close to the limit) I take small shallow breaths, less than normal breathing. There is no urge to gasp.

In all the blackouts I have seen or done, there has been no noticeable inhalation of water. Of course the aim is to rescue the person immediately, but there are a few seconds before it is obvious that there is a problem, and it may take a few seconds to get them to the surface. This shows that gasping doesn't happen at the moment of blackout or LMC.

Lucia

I'm wondering if the article is only true for SIDS age infants. Perhaps as the infant grows to the toddler stage, the CO2 sensitivity (gasp reaction and diaphragm contractions) becomes more and more significant, while the O2 sensitive reactions diminish. The article doesn't even mention CO2, so its hard to tell.

Regarding infants, I meant infants have neonatal reflexes (bright light-blink reflex, loud sound-moro reflex), but not a specific startle-gasp reflex. Children and adults do have this startle-gasp reflex.

DDeden

 

[naiad]

..........

 

[trux]

Maybe. Low O2 can also cause contractions and the urge to breathe, but for me it is a different feeling from high CO2. I described it a bit more here.

Hmm, I am not quite sure if this is true. At least I never saw it mentioned in any article speaking about hypoxia. If you rely just on your personal experience, then it can be easily subjective and misleading. If there is any physiology article confirming it, I'd like to know about it though. As far as I know hypoxia does not cause any urge to breath - that's why you can die very easily and without warning when you breath by accident inert gas with low or no content of oxygen. Same goes for many freediving blackouts and deaths after hyperventilation - the brain simply does not get any signals about the coming hypoxia when the CO₂ level is still low.

 

[wet]

Trux, I think I agree with you, but I just found this message from the vasoconstriction thread, from Wes, and I've heard other similar things, so I'm still not sure, maybe there is a weak O2 sensor to inhale (?): [DDeden]

Edit: Wes, are you online? Can you clarify this? Seems like it is still the CO2 that causes the inhalation.

An Emergency room doc recently told me that people with emphysema (usually from smoking too much) that have a very hard time breathing eventually loose the urge to breath from C02 as thier inefficient breathing always leaves them with high residual C02 so their bodies become numb to it. The urge to breathe is from a lack of oxygen not build of of C02. He said that when treating them in the emergency room if you give them 100% oxygen they take one breath and then stop breathing as they have plenty of O2. This bothers the docs so they give them a mix of O2 with high levels of C02 so they breathe more and fully oxygenate themselves better. This numbing to CO2 build up could explain the benfits of C02 training and also the lack to breathe after training that I have experienced also (though never measured). Wes

 

[wet]

Maybe. Low O2 can also cause contractions and the urge to breathe, but for me it is a different feeling from high CO2. I described it a bit more here.

From the "inhaling CO2" thread, Andy says this:

"I tried a soda syphon bulb as they are cheap and a clean source of pure CO2. I bought a bunch from a local super market but haven't been game to give it another go. I did three pure CO2 holds with about 3mins recovery each time and they were all less than a minute and with instant strong contractions. The CO2 leaves that soda water taste in the back of your throat for quite a while and gave me a 24hr headache....not sure if there is any future for this type of training
__________________
Andy "

This sounds like the CO2 alone caused his contractions, since his body would still have plenty of O2 (I don't think he was anaerobic so quickly).
IOW, it wasn't lack of O2 but rather the high CO2 that caused the early contractions and short breath hold. AFAIK, people who die from anoxic fumes (except CO2) don't have contractions (but I'm not certain).

DDeden

 

[naiad]

As far as I know hypoxia does not cause any urge to breath - that's why you can die very easily and without warning when you breath by accident inert gas with low or no content of oxygen. Same goes for many freediving blackouts and deaths after hyperventilation - the brain simply does not get any signals about the coming hypoxia when the CO₂ level is still low.

I have only sometimes had a 'hypoxic' feeling, sometimes I have had no warning at all. This is why I am very careful, because there is no reliable warning. It really is possible to blackout with no urge to breathe.

 

[wet]

Maybe. Low O2 can also cause contractions and the urge to breathe, but for me it is a different feeling from high CO2. I described it a bit more here.

Eric F. mentioned this in the "Measuring CO2 Tolerance.." thread:

"Remember that low SaO2 causes contractions by itself; the CO2 level amplifies it. So CO2 alone is not enough; likewise, at hyperbaric O2 levels, the high O2 delays the CO2 breathing reflex. This is why both O2 & CO2 must be known, or at the very least, O2 must be fixed."

From the "inhaling CO2" thread, Andy says this:

"I tried a soda syphon bulb as they are cheap and a clean source of pure CO2. I bought a bunch from a local super market but haven't been game to give it another go. I did three pure CO2 holds with about 3mins recovery each time and they were all less than a minute and with instant strong contractions. The CO2 leaves that soda water taste in the back of your throat for quite a while and gave me a 24hr headache....not sure if there is any future for this type of training
__________________
Andy "

This sounds like the CO2 alone caused his contractions, since his body would still have plenty of O2 (I don't think he was anaerobic so quickly).
IOW, it wasn't lack of O2 but rather the high CO2 that caused the early contractions and short breath hold. AFAIK, people who die from anoxic fumes (except CO2) don't have contractions (but I'm not certain).

DDeden

 

[trux]

As I already wrote above, and as far as I can verify in literature, you won't feel any urge to breath, contractions, or other clear early signals about hypoxia just because of the lower oxygen level. This is why I consider the claim that there are two types of contractions (hypercapnic and hypoxic) misleading and very dangerous. Unless it can be proven by referring to medical documents, I'd prefer if the claim was retracted, because someone who reads the thread without full understanding, could put himself/herself into serious risk if he/she relies on it.

Also, I have to warn you about experiments with breathing CO₂! CO₂ at higher concetrations is toxic, can cause serious health problems, and can be even fatal. Generally, concetrations over 10% are considered toxic; some sources refer even to levels over 6% as toxic. Acute carbon dioxide toxicity is sometimes known as choke damp, an old mining industry term, and was the cause of death at Lake Nyos in Cameroon, where an upwelling of CO2-laden lake water in 1986 covered a wide area in a blanket of the gas, killing nearly 2000 ([ame="http://en.wikipedia.org/wiki/Carbon_dioxide"]source[/ame]).

 

[naiad]

Pure CO2 holds? Even I don't think I'll be trying that soon! :crutch
I certainly wouldn't recommend anyone to do that.

I didn't say that there is any reliable warning of low O2. I know from experience that it is easily possible to blackout with no warning signs of any kind.

 

[wet]

Comments on information at this link on hyperventilation?
Hyperventilation - makes you feel as if you can't get your breath | Dr Myhill

Trux, which claims would you prefer to be retracted? I'll gladly remove any that I've copied here, but not sure what is incorrect.

Yes CO2 inhalation is dangerous in higher than ambient air proportion.

DDeden

 

[trux]

Trux, which claims would you prefer to be retracted?

I meant the comment made by Naiad: "Low O2 can also cause contractions and the urge to breathe" and then also the discussion in the other thread. I know it was written with good intentions, and I am sure that it was what Naiad felt to be true, but I am afraid it is a too subjective experience and the conclusion that the contractions were bases on hypoxia are not well based. I respect Naiad, and so do many others here, and that's why such a claim may be dangerous. Many newbies not knowing any theory, seeing Naiad's reputation can take the personal claim for a fact, which could have bad consequences.

I think it is fine if Naiad believes that one can get contractions from hypoxia, but I think it should be clearly put in context that the personal opinion is in direct conflict with known scientific facts, and that it is nothing else than a personal view based on feelings, and not a fact supported by any measurements.

I apologize to Naiad for the bashing on the details, but I really think the topic is quite important and deserves proper precision.

 

[naiad]

I meant it as a personal opinion, not a scientific fact. I did say 'I think', not 'It is'. I will delete it in this thread, but I stand by the fact that there are many, many posts on DB which could be dangerous if taken out of context or obeyed without question, about topics like diving alone, packing, pushing the limits etc. Anyone who mentions packing in any context is giving potentially dangerous advice, as it can be responsible for lung injury, blackouts and possibly DCS.

I did state in both threads that there is no reliable sign of hypoxia, and that I have blacked out with no warning at all.

Lucia