Since practically all my touring is above 10k, I almost always use oxygen. O2 level can vary but it’s always above 90% depending on breathing pattern, usually around 95%. Coping with lower level is very individual and my wife does significantly better than I do.
Absolutely. If I am doing an IFR (high altitude; not Shoreham to LFAT at 5000ft 
) flight, accepting oxygen is mandatory.
Not having oxygen halves the operating ceiling and pretty well buggers up wx avoidance options.
That video seems like bad practice to me. They were at 12K feet, with an O2 system onboard, but but it wasn’t set up and ready to be used.
So for some periods there was noone monitoring the flight, while the pilot tried to manage a hypox passenger while trying to setup the system.
I also wonder what would happen if they both had reacted the same way. It would have been much better to have the system set up and ready to use if it became necessary.
This is a topic where it is easier to describe the solution than to define the problem. This may be in part due to the solution being amenable to an engineering approach, but the problem being a complex physiological/molecular biology interaction not readily amenable to a mechanistic engineering approach. There may be AI/machine learning approaches with potential to describe/predict, but not explain (yet) some of these phenomena.
A very interesting solution.
I’ve got an oxygen concentrator, Innogen One G5, and it seems to be a good device. I use it any time I plan to go outside the flatlands. My initial testing at about 14.5 took me from about 85% to 99%. After a few seconds, you don’t even notice it. Battery for about 3-6 hours, and I plug it into the aircraft 12v for “unlimited” O2. New it’s about 2.5k USD, I found a “used” one for 1.5k Euro in France on leboncoin.fr. It was new, but the box had been opened. Happy to provide more details if anyone is interested.
I have regularly flown at FL100 without oxygen before getting an oximeter. When I did, I noted to some surprise that I got values below 90%. Of course, I know that you don’t realise when you’re (slightly) hypoxic, but in retrospect, I can’t see that I made any bad decisions on such flights. (At least not worse than when I fly at low levels. )
On the other hand, when I once flew as pax at FL130 for several hours I did note a marked tiredness and lack of concentration that disappeared when I used oxygen.
Snoopy wrote:
Younger people show worse effects than older ones.
There might be also a significant “training effect” involved in that: A surprisingly high percentage of elderly people (esp. male) suffer from some form of sleep apnea (often undiagnosed) that leads to alarmingly low levels of SpO2 during some phases of the night. If your body is used to 2-3hrs. of 70% SpO2 every night, it is much easier to cope with 70% SpO2 due to low pressure environment in high altitudes…
