Post
by cinnabar » Mon Sep 26, 2005 12:09 pm
Ozij, I think you are onto one of the many issues that can contribute to this problem. The more upward pressure an interface puts on the upper lip, the easier it is to push air out through the lips. (And the anatomy of each individual's lips also plays into how much this matters as well.)
I, too, am a Swift user who has experienced the dreaded mouth flapping. I noticed it most after I moved from a fixed CPAP at pressure 8 to APAP ranging from 6 to 12. Now, I average 8 (my titrated level), but my 90-percentile point hovers between 9 and 10. I get better therapy (AHI numbers) but I experience more "blowouts" and now use a chin strap. (This corrects most of them, but not all.)
I assume higher pressures will contribute to the problem. Those of us averaging pressures of 10 or higher probably encounter this phenomenon more often than those of us hanging out in the single digits.
Another factor I suspect (but cannot prove) is involved: Turbulence. Turbulence is a chaotic and tricky thing to quantify. But from my own experience and from what I've read on this message board, I suspect the Swift generates one of the more turbulent air flows of any of the popular nasal interfaces on the market today. (I also think that turbulence is the reason the Swift gets so much noisier at higher pressures.)
All nasal interfaces must generate the same level of air flow in the nasal cavity and throat to achieve the target pressure in a specific patient's airway. IMHO, some produce more turbulence than others while doing so. To move thru the Swift, air must take two right-angle turns in quick succession: one when exiting the air tube attached to the side of the mask and another when entering the nares. This extreme zig-zag means the air molecules are literally "bouncing off the walls" as they enter the airway at the target pressure. And the higher that target pressure, the more they "bounce."
Now, consider the airflow path thru masks like the Aura or the Breeze (neither of which I own or have used). For them, that flow path is more curved with less right angles. Less bounce, so less turbulence.
So is the turbulent air pressure from the Swift more likely to push open the lips now and then, versus the equivalent but "calmer" air pressure from these other interface designs? As I said, I can't prove it but I suspect it's a factor. And in the absence of comparitive experimental data, reading the experinces of those who have used both masks (like LoRi) are one way to confirm or deny that suspicion.