Carbon dioxide question

[blueface]

Carbon dioxide does two things (as far as I know) that help keep a freediver from blacking out.

1. When the level of CO2 rises receptors sense this and trigger a breathing response.

2. It has an influence on the Bohr saturation curve and helps the alveoli to bind with the O2 better.

Which has greater significance? If a diver hyperventilates and blacks out, was it because of getting the "urge" to breath too late? or is it because the O2 is not binding as well because of the low CO2? Does it depend on too many varibles to answer?

Sorry if this question is confusing. :head

Skip

 

[DeepThought]

I would rephrase 1 to "triggers the dive response (=DR)".
As for number 2, you got it the other way around: rise in CO2 results in lower affinity between hemoglobin and O2, which means that more O2 is available to the tissues at lower blood O2 saturation levels. Oxygen-haemoglobin dissociation curve - Wikipedia, the free encyclopedia

As for which is more effective in a given person, I don't know.
I would GUESS that the DR contributes much more to one's performance over all, considering the difference of DR intensity between a novice and an elite diver are probably very significant, while there's no current knowledge on any typical difference between blood pH and buffer capacity of elite vs. novice divers.

 

[trux]

Yes, what DeepThough writes is correct. High CO2 shifts the Bohr curve into the other sense - blood actually binds the remaining oxygen in lungs less, but releases it easier in tissue.

As for the first point, I would actually split it into two different ones:
1a) High CO2 triggers the urge to breath quicker, hence providing early signal to surface - this is especially important at recreational diving or spearfishing, because without the early signal (i.e. after hyperventilation), you can easily get into the deadly zone of SWB. Performance-wise, this effect is not really welcome, because it does not help you stying down longer, but rather the opposite. It is the increased safety that's important here.

1b) High CO2 stimulates early and deep Diving Response, reducing so oxygen consumption, and increasing the time you can spend down.

 

[efattah]

Simple answer --> for a full lung breath-hold, a diver who hyperventilates will black out earlier than a diver who doesn't.

Doesn't hold true for exhale statics though, at least not for me.

 

[blueface]

Thanks for all the resposes!

If I were to rephrase no. 2 would this be right?

2. It has an influence on the bohr saturation curve allowing for O2 to be released in the tissues easier.

If it weren't for no.2 we would probably see a lot more divers blacking out. Is this correct?

I had no idea high CO2 triggered early and deep diving response. Thanks to all.

Skip

 

[trux]

I had no idea high CO2 triggered early and deep diving response.

Well, not alone, but it is one of the factors playing a role.

The rephrasing is ok. You can also tell that high CO2 helps supplying organs and tissue with oxygen even at progressing hypoxemia that would be otherwise already critical and would cause blackout.

 

[blueface]

Thanks DeepThought, trux and Eric! It is a real priviledge to get answers from you guys.

Skip