About hyperventilation

I'll take a laymans shot at that.

The body has two separate sets of sensors for gas levels, c02 and 02. The co2 ones come on sooner and are louder and more insistent than the 02 ones. When you do extreme HV, the body thinks it has plenty of 02 and burns it fast until 02 levels are very low and the 02 sensors start going off. That too late for our purposes. Further, you might not recognize the 02 sensor alarms. Further, further, low co2 levels make the 02 that is there less available to the tissues, so it might as well not be there, reducing safe dive time. Lessor levels of HV tend in the same direction. Further, low c02 affects vascular circulation in ways that are negative to long breathholds. You can see that by extreme HV that creates the tingles and vision problems. These are directly caused by low c02 constricting the carotid arteries, restricting blood flow and 02 to the brain.

If you don't HV, or do it only a little, the body starts the dive with a reasonable amt of co2, 02 conserving mechanisms( such as dive reflex) start early and the available 02 lasts longer, more of it is available to use, resulting in safer, longer dives, the early stages of which might be less comfortable than if you HV.

Connor

Saleh, you are right that the reaction on the hyperventilation is higher affinity of oxygen to hemoglobin, but it does not necessarily mean that the organism consumes less oxygen. There is plenty of O2 in the hemoglobin in that moment (practically 100% saturation), and the blood flow is elevated (except of the cerebral flow that is in contrary diminished), which still permits the organism to consume the O2 despite the higher affinity of O2 to hemoglobin. It contrary, the high HV, due to this high affinity, leads to depleting of local stores of oxygen (especially myoglobin), before you even start the breath-hold, adding so to the other negative effects of the HV.