Why adjust the pressure range on APAP machines?

I still don't understand the very basic theory of narrowing the pressure range on an APAP machine. If the broadest APAP range is say 5-20, and the machine is designed to adjust to the user's needs, why would you narrow that range? It seems you're crippling its flexibility.

My DME said that they usually set the APAP machines to a 5-20 range unless instructed otherwise (which they usually aren't). My sleep doc is also happy with it. Of course, that doesn't make either of them right. Just reporting.

Besides, my quality of sleep isn't great, even though the numbers check out (AHI <1.5, pressure ~6, leak median zero). Therefore, my question has a self serving component, but I'm also interested intellectually.

I know there are reasons for narrowing the range, since it works for some. I've read those reports on this forum, but I haven't discerned any clear and consistent rationale.

For reference, there were prior discussions and and a survey about this:

viewtopic/t51755/POLL--Do-You-Have-a-Narrow-or-Wide-Xpap-Pressure-Range-ed.html

However, I'm still looking for some simple explanations I can get my head around.

Gerry

I can't speak for the Respironics, but I'm sure the response is similar. APAPs do not just jump from 5 cms to 15 cms if it happens that 15 cms is needed to clear an event. They proceed cautiously, if I remember correctly, 0.2 cms at a time. Set the range too far apart and too many events occur before the APAP has gotten up to the pressure needed to stop the event. At least that is the way my beady little brain understands it.

My understanding is that the machines tend to deliver pressures that are too low when they are set at a wide open range (perhaps for reasons mentioned above). Also, for many people, wild changes in pressure tend to disturb their sleep.

Did you have a titration in the lab? If so, you could set a tight range around the pressure you were told is right for you (eg, 6-8) and look at the data.

Some more mental stimulants:

My case: titration study called for pressure of 8. My APAP is set for 5-20. I have no ramp and don't feel delay in going from 5 to 6, which is where the APAP settles in. The increases are very slow and deliberate and settle right back to where the stable range is (~6). So even if the upper limit was set at 100, it would never get there. I never experienced "runaway" pressures.

So we now have an answer for raising the low pressure: if someone has a normal pressure requirement of say 12, it might take a long time to get there if the lower limit is set at 5. Check.

Still missing an explanation for lowering the upper limit. Also, some claim that the therapy is better when the ranges are contained. That whole concept still escapes me?

Lowering the upper number may not do anything at all... so most of the comments about narrowing the range are referring to adjusting the lower limit. But, higher pressures can induce central apenas in some people--keeping the upper limit lower will prevent the pressure from going higher so may help in that situation.

Another reason to increase the lower limit beyond what has been mentioned is to increase air flow--I feel like I'm not getting enough air at 5, for example, so I want it to start higher for my breathing comfort... since it always makes it to above 9 anyway and stays there most of the night, there is no reason not to start there.

gpk111 wrote: Still missing an explanation for lowering the upper limit. Also, some claim that the therapy is better when the ranges are contained. That whole concept still escapes me?

For me, I don't want to go above 12 max, because I have experienced painful aerophagia at that pressure. So I am content to hit my maximum pressure and occasionally I get 1 or 2 obstructive apneas per night, rather than go above 12 and risk the pain. But most nights, I have no obstructive apneas, and maybe 1 or 2 central apneas (which I consider normal)

Some people get excessive leaks at the higher pressure, so that may be another reason for limiting the upper pressure.

Now it's starting to make sense..... Thanks......

Good explanations for upper and lower limits.

Now a focus on narrowing the range: eg if the target is 8 and if aerophagia and ramp up is not a problem, is it better to set it at say 7-9 or 6-12?

Set the minimum pressure to where it eliminates almost all of the events.......like one would in CPAP mode. Then, if you need a little more pressure for errant events, you've got some. The APAP may not eliminate them, but it my chase them (raising pressure). Just remember that for solitary ("frank"), 12 second apneas, the Autos will probably not get them or even chase them without preceding snores or flow limitations.


Den

I note on my S9 that AFTER after a normal event, it raises the pressure by say 1/2. After about 30 minutes, it's back down to the lower level, assuming no additional events. In the case of additional events, it's "prepared," but only after about 5 minutes following the event (the chase phenomenon you describe, I think).

That makes sense.

Back to the pressure range setting question: I thought I read here somewhere that a tighter pressure range allows the algorithm to react quicker.??

gpk111 wrote:Back to the pressure range setting question: I thought I read here somewhere that a tighter pressure range allows the algorithm to react quicker.??

This is P-U-R-E Entertainment. Really!!

gpk111 wrote:I note on my S9 that AFTER after a normal event, it raises the pressure by say 1/2. After about 30 minutes, it's back down to the lower level, assuming no additional events. In the case of additional events, it's "prepared," but only after about 5 minutes following the event (the chase phenomenon you describe, I think).

That makes sense.

Back to the pressure range setting question: I thought I read here somewhere that a tighter pressure range allows the algorithm to react quicker.??

That would be why you want to set your minimum pressure to an optimal point. (where it eliminates almost all of the events)
"Reaction time" would be desirable for the rise in pressure.
A "tighter" pressure range (setting a lower maximum pressure) would eliminate the possibility of the pressure rising higher than necessary.


Den