On Saturday, November 3, 2018 at 9:27:22 PM UTC-4, wrote:
BobW: More recent than that, around 2012 or so.

T8: But you can be hypoxic even breathing pure oxygen. Yes, I was part (albeit in a small role) of the research team that lead to a series of articles on identifying white matter lesions in U2 pilots using MRI. These and other published studies convinced the Air Force to change the U2 cabin pressure from ~30K' to ~15K' (similar to Perlan II) fairly recently in a program called "C.A.R.E.". Although these brain lesions can arise via different mechanisms, they are reminiscent of damage resulting from emboli or clots. While the lower cockpit pressure had been used for many decades, one theory is that after 911, these pilots flew more frequently, for longer sorties and were tasked heavily both physically and mentally than previously. And, no, hypoxia is a problem in those conditions. Breathing 100% O2 at sea level is vastly different physiologically than at extreme altitudes since the absolute alveolar PO2 value needs to be at least ~14kPa. Even at less extreme heights breathing 100% oxygen is about as efficient as breathing air at around 12,000ft. Robert Harris for his 1986 49,009ft altitude record flew in an unpressurized Grob 102. He was forced to come down when his O2 system started to fail, apparently suffering from medical issues for some time thereafter.

Original article:
https://www.ncbi.nlm.nih.gov/pmc/art...ihms488856.pdf

Thanks for that!

Following some links, I ran across this statement:
"The DCS risk per [high U2] flight was 0.076% from 1994-2005 but increased to 0.23% from 2006-2010."

That is to say, not terribly common, but not very darned rare.

T8