I would like to add a datapoint to the whole "What is flow limitation" discussion as I improve my own understanding of how to interpret ResScan information. (Or more accurately, S9 Autoset information. ResScan is so much like a graph displaying tool and so much math is done inside the APAP, it's not even funny. I have yet to see what math/analysis ResScan is actually doing.)
I was doing a fixed CPAP pressure of 7.0 and before the clusters of apnea events (central and non-central, appears more with non-central though) I see a flow limitation of at least 0.5. (It starts at 1.0 and slopes down to 0.5 in about 15 minutes, nearly linearly.) This happens almost 15 minutes before my "apnea attack" every time, consistently. I've examined the detailed flow data closely, and I do see the difference in the squared off edges and round edges during times of my normal breathing.
I then switched to APAP (min=4.0, max=12.0) and I still have some apnea attacks with clusters of events, but the flow limitation stays more than 0.90 the entire time. (higher = better as this means no detected limitation.)
I would guess this means that APAP with some sort of a range actually gives you less of a flow limitation. I've read some research papers before that basically said CPAP and APAP are equally as effective. My findings above almost seem to indicate that it's more effective.