The hose clenched in the teeth idea - although unrefined- does have some physiologic advantages. The little bag below the mask or the long wide hose below the military masks are reservoirs, tanking up the delivered O2 while you are exhaling and upon inhalation delivering a higher FIO2. The clenched hose in the mouth idea uses your mouth and nasopharynx as a reservoir also and increases the percentage of inspired O2 beyond what the nasal cannula can do in your nose. In a pinch, if you just have nasal cannula (the old school continuous delivery ones) and you are 18,000 feet or higher, just put the cannula in your mouth, inhale like taking a draw on a pipe and exhale through your nose. I’ve been able to maintain 95% or more O2 sats or more at 20,000 feet in my turbo Viking a few times… at least that’s what I remember….
just some physiologic nerd stuff…..