First though, the leaks: consider Full face mask
Exhale. The nasal airway is locked and mouth is closed, the machine will detect the lack of flow..(In my case , with an ASV, the pressure starts varying to induce breathing.) Body reacts to apnea and mouth opens - nasal airway remains closed, but mouth airway is open.. Air under pressure rushes in and fills lungs.. Machine records event as a UA, and posts the pushed breath as a small leak.
Here's how I stumbled into understanding this: While playing with a nasal mask and a normal CPAP machine, I discovered that I easily and almost reflexively can close off the nasal airway above the tongue. In other words, I can talk, eat, drink, and whistle dixie like normal with a nasal mask on and CPAP running.. To some of you nasal mask users, this may seem like a super power. For me it's annoying.
A couple weeks ago, I woke up in the middle of what was recorded as an apnea, and aware the flesh of the soft palate was vibrating with the airflow - I now understand this.
During the sleep study /titration, when the tech first switched me to ASV, and I aroused later, I was 'fighting' or resisting the machine's pushing of air to force me to breathe.. I complained to the tech, and he said I was leaking, and cinched down on my mask - which I didnt really think was necessary.. I suspected then that somehow when I was fighting the machine, it was showing a higher leak rate. I understand this now, as described above.
Now, while my physiology might be rare (apparently), I would suspect that nasal mask wearers might actually show an apnea when they are actually mouth breathing.. I doubt that I'm the only one who can lock the nasal airway. Looking at other instances where people discuss things like not being able to talk with a nasal mask on - Hell, I can whistle dixie with one on and the machine at full pressure.. not to mention drink, talk and eat (awake of course)...
I'm betting this is new news to you guys..