Apnea with pure oxygen

[mimmo]

Breathing pure oxygen, the apnea duration increases a lot so, I would like to ask, why in this case the hypercapnic limit does not intervene to determine the breakdown of the apnea?

 

[Hyscore]

Breathing pure oxygen, the apnea duration increases a lot so, I would like to ask, why in this case the hypercapnic limit does not intervene to determine the breakdown of the apnea?

I think it probably does. If you breathe up on pure O2 it is akin to super-hyperventilation. Not only are you increasing the percentage of O2 in your system you are also flushing out CO2 leaving it at a very suppressed level. Once you are in the breath hold the CO2 will build up at the normal rate, but because it is starting at such a low concentration it will take longer for the CO2-driven impulse to breathe to be felt. This answer is based on very basic snorkelling physiology so I too would be interested in seeing an answer from a medical professional or similar. We are taught that hyperventilation is dangerous on account of the urge to breathe being suppressed to the point that the reduction in ppO2 on ascent can result in a shallow water blackout. Would the same be true for someone who has breathed up on pure O2, or would the CO2-driven impulse to breathe occur before O2 levels fell dangerously low?

 

[J Campbell]

World record breath holders on O2 go for around 24 minutes. Do these guys still get the painful urge to breathe after a few minutes, even though the total breath hold lasts much longer? And do they still get contractions at the same time? It may be a very painful experience!