Jim and Scott,

Yes, I am well aware of the dangers of hypoxia and my own symptoms of it from my USAF pilot training.  I have a quality oximeter and monitor myself and my wife regularly.

Also, Jim, I had already read the OK-09-439 document.  That document also claims that cannulas are restricted to below 18,000 feet by regulation, but then never cites a reference.

So, while I am very careful at altitude, I guess the conclusion is that the use of cannulas, in an experimental at any altitude, is legally up to the pilot.

Tom