I'm going to ask my AVMO this tomorrow, but I'm curious: In the section on G Loads the book says that the brain is sensitive to lack of O2 and responds to it by increasing pumping rate. However during exposure to Hypoxia the brain has no idea it is low on O2 because it is only looking at the CO2 ratio in the blood supply. In the case of G, is it a case of the O2 not making it into your system because of the G effect, and the exertion from the G causing you to breath more creating more CO2 tips the brain off?

I know the CASA exams won't go into this detail - however if I get my QFI posting next year I'll be neck deep in teaching aerobatics and I want to be across all of my theory!

Thanks in advance for your help.

My understanding of grey out/black out in high positive G is that it is related to blood pressure. Our hearts have evolved to pump blood at the required pressure to our brain at +1G and if we sustain high positive G then by the time the blood reaches our brain/eye (above the heart), the blood pressure is insufficient. There is no lack of O2 or excess of CO2 in the blood, simply not enough pressure to force that O2 across the membranes into our brain cells and retina where it is required.