hose diameter

I wouldn't worry too much about the small hose diameter.

(Fact mode) If it's 1.4 times as big as one nostril, then it's equal in cross section to both of them, and will provide no more resistance than your own nose.

(Opinion mode) Plus, I don't think it's the volume of air that makes these tick, as you're always going to breathe in the usual amount. The pressure differential is what makes CPAP such an effective treatment.

(nostalgia mode) The shower in the picture looks like a typical "third world" shower -- in which the water is heated in the shower head by a 240 volt heating element with one setting. If you run the water fast, you get a, um, less cold shower by USA standards. If you run the water at a dribble, then the water can get up to a nice 103 farenheit (or about 40 celsius). Every time I took a shower in Central America or Africa, it was hooked up by the same wire nut splice. I hope (but doubt) that there's a ground fault protector at the other end.

-Tom Williams
(trying to resume CPAP usage after a multi-year hiatus)