(02-25-2013, 09:51 AM)ImReallyTired Wrote: Are there any ASV users out there who can explain the basics to me? I've read and read and somehow I'm still not getting it. I mean, I know what it does and kind of how it does it, but I don't have a good grasp on the relationship between all the settings. EPAP min/max, PSMin/max, BPM etc etc. Right now my settings are:
EPAP min and max both 14
PSmin = 3
PSmax = 10
BPM = auto
Max pressure = 25
Hey, we look like we're twins!
I have been reading up on ASV machines, and also on protocols for PAP titrations.
First, I suggest you experiment with sleep position, with a view toward reducing your obstructive apneas and hypopneas. Usually, sleeping on one's back makes obstructive events more likely. Also, I think the angle of the neck can make obstructive events more likely. Sometimes, reducing large leaks can help reduce obstructive events, but I don't think you are having large leaks.
Second, if you can afford to do so, I suggest getting a wrist-mounted Pulse-Oximeter to monitor your oxygen levels. The wrist-mounted Pulse-Oximeters use a separate cup to hold the sensor on your finger lightly. The finger-mounted Pulse-Oximeters need to clamp themselves onto the finger with more pressure, which gradually becomes uncomfortable, especially if wearing for more than one night in a row, even if one is rotating which finger is being used.
Third, I suggest you ask your doctor to increase the EPAPmax to 15, to reduce the incidence of Obstructive events.
Your machine is presently adjusted to be similar to a BiPAP machine adjusted for 14 EPAP, 17 IPAP, except the IPAP will automatically increase itself breath-by-breath whenever the machine senses you are not inhaling as much air as you have been averaging recently (or not inhaling at least a large percentage of as much air as you have been averaging recently). And, unlike CPAP, APAP or bi-level machines, if you don't start to inhale on your own your ASV machine will step in to increase the pressure to help ventilate you.
Your machine is presently adjusted so that the highest the IPAP will go is 24 (=EPAPmax+PSmax). When we are having central apneas, the PS may need to increase to 10 cmH2O or higher, in order to keep us properly ventilated. That is probably why the PSmax has been set not lower than 10.
If the PSmax were set to 11, the highest the IPAP would be able to go is 25 (=14+11). However, a change like that (raising PSmax to 11) would only make sense if your data were showing that the machine is not able to raise the PS enough to adequately treat your central apneas. The data shows that the central apneas are not being completely eliminated, so maybe raising PSmax to 11 would help the central apneas be treated more completely, but I suggest the greater problem is your obstructive apneas (and hypopneas).
Raising the EPAP is one of the two standard methods for eliminating obstructive events. (The other standard method for eliminating obstructive events is to stay off the back.) Hence, I suggest you ask the doctor to raise the EPAPmax to 15. This would still allow the PSmax to be 10, so your central apneas will continue to be treated as well as presently. By the way, on your machine, the IPAPmax (max pressure) cannot be set higher than 25. For example, one cannot both raise the EPAPmax to 15 and raise the PSmax to 11, because those would add up to 26, which is higher than 25. The EPAPmax could be raised to 16 to further reduce obstructive events, but not without lowering the PSmax to 9, which wouldn't be able to treat central apneas as strongly.
Fourth, the other problem (at least, I think it is a problem) is the unusually low breath rate (breaths per minute), which sometimes drops to 7 or 8. I think a more common low breath rate when in deep sleep is between 10 to 15, and, as long as a higher backup breath rate does not become bothersome and does not cause you to wake up, you may do better if the doctor sets the backup breath rate to 10 or higher, instead of leaving it set to automatic. "Automatic" means, when you stop breathing the machine will step in and continue your recent breathing rate (which may have been too slow to provide good oxygen levels in the blood).
The tidal volume (Vt) is the volume of air you breath in (or out) per breath. The tidal volume times the breaths per minute (BPM) is the minute volume (Vm), the volume of air you breath in (or out) per minute. Your minute volume sometimes dips pretty low, and I think increasing the backup breath rate to 10 or higher would probably improve this, and thereby improve your oxygen levels.
And fifth, another thing which may help you stay more well ventilated may be for your doctor to increase the PSmin. If any significant amount time is being spent with the PS near it's minimum, I would expect that increasing the PSmin would tend to increase the tidal volume and the minute volume, and therefore your oxygen levels, during those times. Also, I suspect raising the value for PSmin may help reduce the incidence of hypopneas, if the hypopneas are more prevalent when your PS happens to be low.