(09-11-2013 05:05 AM)SleepQuest Wrote: This is the second night I have used my new Resmed S9 machine and I'm having an awful time with air pressure problems. I experience periodic strange "snoring" or something flapping in my throat, sensations of pockets of air caught in my throat...
Hi SQ, welcome to the forum!
All ASV machines are bi-level (BiPAP or VPAP) but not all BiPAP or VPAP machines are ASV.
For ASV bi-level machines like yours (and unlike machines which are not ASV, such as CPAP, APAP, standard BiPAP and standard VPAP machines), the pressure tends to increase with central apnea events the same as it does for obstructive events, which is to say the pressure increases immediately, perhaps zooming up to full pressure in a few seconds (to whatever pressures it needs to go to, to reestablish your normal rate of "tidal" airflow in and out of your lungs). This is what takes time to get used to, when switching to an ASV machine.
So if you pause to swallow or anything, the machine will jump on top of that. Eventually we become accustomed to the machine. For example we learn to time our swallows to occur (mostly) between breaths, and it does not surprise or annoy us as much when the machine does its thing.
Regarding the flapping you mention, I think it appears that the EPAP pressure is too low.
My ASV titration results pointed to an EPAP pressure which actually was far loo low, so my first ASV prescription set the EPAP pressure far too low.
The technician who performed my ASV titration (before I got my machine) never raised my EPAP above 7. This was even though, before the titration started, I had shown him a ResScan report that showed my auto machine was automatically adjusting my EPAP up to 13 or higher in order to prevent obstructive events. Nonetheless, the technician followed the standard procedure, which is to start with EPAP of 6 or lower and increase the EPAP only when actual apneas or hypopneas occurred. I think this is the standard procedure used in many sleep labs, and it is a faulty procedure, since it is a carryover from earlier, non-ASV titration procedures. The sleep lab's standard ASV titration procedure ignored the difference between ASV and non-ASV treatment, which is that ASV treatment will prevent hypopneas even when the EPAP is too low.
The standard procedure allows for the referring doctor to specify a higher starting EPAP which has been determined from earlier CPAP/APAP therapy results, but the doctor didn't bother to do this, so the ASV titration was started at a very low EPAP pressure.
ASV tends to prevent obstructive apneas and obstructive hypopneas even if the EPAP pressure is way too low. If an ASV machine's EPAP pressure is too low it can cause the flapping you describe (the flapping which occurs in the throat, not in the mouth or lip area). This occurs because the airway is intermittently closing during exhalation, yet the ASV treatment is able to force enough airflow to avoid actual apnea or hypopnea. This intermittent obstruction is bothersome and I think it may prevent us from reaching deep, restorative stages of sleep.
If the technician is keeping an eye on the Flow curves and increases the EPAP pressure high enough to prevent Flow Limitation and Snore, then all will be well. But I wasn't lucky enough to have used a competent technician and sleep lab.
After I got my machine, when I looked closely at the Flow waveforms (using ResScan), I was able to see immediately that the EPAP was way too low. Instead of smooth inhale and exhale curves, there were times when my exhale curves were ratty, rough, intermittently jumping back and forth between zero (no air being exhaled) and more air being exhaled. (On a Flow plot, positive values represent inhalation, and negative values represent exhalation.)
After I adjusted my EPAP pressure to 13 or above, like my APAP had determined was sometimes needed to prevent Flow Limitation and Snore, the Flow curves stayed nice and smooth all night, indicating that my airway was remaining unobstructed and air was able to pass through my airway freely.