[trux]

Yes, I agree that some level of hyperventilation or a purge breath may be needed to accelerate the gas exchange, but in contrary I think it is better after the previous performance to quickly blow away hypoxia and toxins including excess CO2. I used to do purge breathes just before the apnea, and almost all freedivers I know do it too, but the more I read about diving physiology, the more I see that it is actually counterproductive.

The volume of oxygen you gain with the last purge of hyperventilation is not big, but the level of CO2 may rapidly drop, with the consequence of carotid arteries contraction, higher blood acidity and the resulting lower oxygenation of brain, tachycardia, and especially considerable delaying or partial or complete suppression of the diving reflex.

Just read some posts of Sebastien Murat or Will Trubridge who advertise FRC and slightly hypercapnic diving. I think also Will Winram applies these methods, though am not sure now. Or read the article about Murat's school of diving at the link I posted in my previous message.