I started with Bipap.
Prior to my titration, I made an appointment at the sleep lab to try on masks and find one that would work for me, since I knew from reading this Forum that the mask is one of the primary keys to making this therapy work.
When we went to test the masks under pressure, I could not, absolutely could NOT, breathe out against whatever pressure he was using.
So, he switched it over to bilevel pressures, and I was able to find a good mask, in fact, the one I used for the first six months, and which is still a favorite mask.
I was titrated bilevel, and then they looked at the fact that I had buckets of centrals, and decided to put me on an ASV machine.
It worked great for me -- I was sleeping the night through on it by the end of two weeks.
My pressures weren't set correctly for the first 10 or so days... but I checked my readouts via my software, and was able to discuss the issue with my RT and my doctor, and we changed the pressures to the ones I am using today, 3.5 years later.
So bilevel is not necessarily for people with high pressures.