On mountaineering trips we would often have O2 saturation levels in the 80s
(some people low 80s) upon reaching a new altitude. After a day (or three
sometimes) it would recover to the low 90s. Then we could go up another
thousand meters. This went on for weeks. I don't think that it is
cumulative.

Mike
MU-2


"PaulH" wrote in message
om...
I took my Arrow up to 10,500 today to check out my fingertip O2
measuring device. I can maintain 90-93% saturation with deep
breathing and no supplemental O2. Anybody know what the minimum safe
level is for daytime? I guess it might be cumulative, i.e. the longer
you go at 92% the less safe it is? Dropped down to about 88% when I
got distracted with some cockpit chores and started normal sea level
breathing.