Karl´s Rebreather Page

Breath-Holding and the Influence of the Oxygen-Partial-Pressure

Some OC-SCUBA-Diving books still teach that the breath-holding time is independent of the ppO2 in your lungs, but this is only true as long as you speak about Oxygen-Partial-Pressures that are lower then in normal Air.

If you for example breath pure Oxygen at the surface you will notice that your breath-holding time increases significant. That effect is caused by an inhibition of those ppCO2-Sensors that control your breathing.

That effect is good and bad at the same moment:

It's a danger for apneu deep-divers (although they breath air) because the depth-caused ppO2 inhibits the breathing-stimulus, so that the divers feel to have endless air and risk to faint on the way to the surface then the ppO2 comes back to the reality.
It increases the danger of negative high-ppCO2-effects like higher CNS-Tox-Risks.
It gives the diver more time to solve problems (or shoot photos) that need breath-holding.

Average values you know from those books that do not mention the influence of increased ppO2 are about: normal breathing-stimulus at ppCO2=0.04bar, invincible-strong breathing-stimulus at ppCO2=0.08bar, fainting-level at ppO2=0.05bar.

Divers that can hold their breath about 3minutes after they have breathed Air will be amazed notice to be able to do about 6minutes after breathing pure Oxygen (the test was done at the surface).

A graphic drawing of the blood-ppO2 & -ppCO2 during pure-oxygen breath-holding will follow later.

Rebreather-Index