A useful chart (for me)

Most of you are probably getting thoroughly bored with my quest to understand what PAP does to reduce the A's and H's Too bad...

So let's atart with the premise that each individual has a basic statistical relationship that describes the frequency of events as a function of PAP pressure. In other words this is a description of how the AHI will change (on average) as the PAP pressure is increased. There are all sorts of variables of course, such as sleep position, etc, that will affect the value, but let's not get too bogged down in the details for now

So anyway, last night I got out my Encore Pro data for the past month. For each night I took the pressure dependence chart at the bottom of the daily detail report, and used the first row to find the "time at pressure", and the last row as the AHI at each pressure.

I then created a spreadsheet and computed the total nightly events for each pressure (AHI x time at pressure) and then for the whole month computed the AHI (total events/total time at pressure) at each pressure, and made the following plot:



which is a nice clean plot that shows my average dependence on PAP pressure. Very useful. I also show a straight line approximation to the curve.
(There is a small problem in that Encore Pro only reports pressures in 1cm increments, while the REMStar Auto uses 0.5cm steps.)

So I said (to myself - because nobody else cares ) let's shoot for an AHI of 1.5 tonight. The chart predicts that I should use a PAP pressure of 8.5 cm. I set that as the minimum pressure on the REMStar Auto, and this morning my AHI showed as 1.8. I thought that was pretty good because the chart gives just an average picture.

My point is that I think a chart such as this is a pretty good prescriptive tool for setting the minimum pressure on an APAP. You get to trade off comfort against a target AHI level.

derek

Derek,

I know that there are at least a few of us on the forum that are on the edge of our seats waiting for your next PAP revelation. Your current analysis is very interesting. One conclusion that I draw from this data (I assume you concur but didn't mention it) is that you would receive maximum benefit from xpap at 10cm. Anything beyond that would just be adding more pressure without better results. The question I have is would 10cm be considered the fixed pressure you should be at or should it be the pressure at which you reach an arbitrarily chosen acceptable AHI number? Or would anything in between these two number be acceptable depending on whether your goal is to minimize AHI or minimize pressure. Or further, is this the range at which optimally the APAP should operate to both minimize AHI and pressure?

Very nice predictive method using statistics, Derek. Thank you very much!

You had mentioned a trade off between AHI and comfort. Have you been able to discern any subjective difference between how you sleep/feel at a lower AHI of around 1.5 or 1.8 versus a higher (but acceptable) AHI of 3.5 or more?

You must be an engineer. As a fellow engineer I thought about doing a study where I vary the angle of my mattress and see how the optimum pressure varies. The only problem is I have a waterbed. Anybody else want to give it a try?