decrease heart rate after strong effort under water

[The Chairman]

Heartrate is linked to oxygen consumption.

Chemoreceptors in the brain are largely tied to CO2 and not oxygen. This is why we can go on %100 surface O2 and not feel weird. The more oxygen you metabolize, the more CO2 you produce. IOW, a build-up of CO2 is what causes you to want to take a breath... not the lack of O2. In fact, if your O2 is off on your rebreather, you'll probably never know unless you monitor it via working oxygen cells. You'll simply go to sleep, never to awake never knowing your O2 is so low that it won't support life.

 

[chillyinCanada]

When I go deep or have to exert myself for some reason, I concentrate even more on my breathing and more slowly draw in and more fully exhale. This has always protected my air usage and made me feel better on the whole.

That said, I have been known to completely stop, even head down feet up and do nothing more than concentrate on breathing fully out and draw slowly in again until i have recovered from whatever excitement ie current/shark activity etc. had caused my heart rate increase.