Eleven years ago I did my Sleep Study......it was a combined Sleep Study imediately followed by CPAP Titration in one night. My Titrated CPAP pressure ended up being 12cmh2o. All fine and well.....went home with an old Resperonics Brick set at 12cm and was Fat, Dumb, and Happy for years. Then it was time for a new machine after five years and I got an F&P Icon Auto when they first came out. I was totally fed up with Crapria (Apria) by that point so I struck out on my own with the help of this Forum. I set my Auto Icon up with a reasonable range of 8cm to 14cm, all is well, again I am Fat, Dumb, and Happy. I was looking at AHI numbers just from the screen of the F&P, but decided to install F&P's InfoSmart software so I could keep a closer eye on things......that was all good and I could see that my 90% pressure was indeed around 12cm and never went much higher....AHI numbers were good around 1.3 average overtime. Mostly I was having Hypopneas and very few if any Obstructive Apneas.
Then a couple years ago I aquired and S9 Autoset and began using that machine as primary and the F&P as a travel and backup. At that time Sleepyhead worked fine for the S9, but did not at that stage work for the Icon. Now I learned that different brands of machines have different Auto Algorithms and that's very understandable, so I wasn't shocked that the S9 wanted to go up above the 14cm upper range......I let it go higher and started to see more Centrals and I started to have more arousals due to increased leaks with my FFM. So since my Titration pressure was 12cm I decided to cap the upper range at 13 on the S9 so the machine could not go to higher pressures. Again all was well, the AHI numbers settled down to a nice 1.3 ~ 1.4 average. Occasionally I would even get some great AHI numbers like 0.3, so I was feeling good and thought things were well in hand. Very few Obstructive apneas, again mostly Hypopneas and a few scattered Centrals that I wasn't worried about. Most of my AHI number was made up of Hypopneas, and they were pissing me off simply from a numbers stand point.
So I have been experimenting of late with my new Airsense autoset machine, and same thing probably because the auto pressure algorithm is basically the same as the S9 I suspect.....the machine wants to keep going to higher numbers like 14 ~ 15 cm if I let it. I have the minimum set at 11 so as not to have too wide a pressure range. But when I let the pressure go higher I am seeing a ton more Hypopneas and a few more centrals start to show up and the AHI number after two weeks with higher pressure was getting in the 2.8, 2.9 range. Still acceptable, but not as good as when I limit the high pressure to 13.0 cm.
So I started to get curious about the Titration Criteria.........how do they determine to stop increasing pressure and settle on a number like my 12cm......if 12 is good, why not 13, or 14? So now to the root of my question......I was always under the assumption that Hypopneas should decrease with an increase in therapy pressue, not the other way around. I know that a Hypopnea is similar to an Obstructive apnea just not as much obstruction.......some references place a Hypopnea at a 50% reduction in flow, others place the threshold at a 30% reduction, both with a minimum of ten second duration. So I have always thought that a higher therapy pressure should decrease the Hpopneas just like with an Obstructive Apnea.
I found the following Titration flow charts for sleep technicians from Resperonics, and if you follow the flow chart they increase pressure from 4cm at 1cm intervals until the Obstrutice Apneas go away and if they increase pressure more they are to go back down 1cm if more Centrals and Hypopneas begin to show up. This seems totally counter intuitive to me .......I can understand that increasing pressure may increase Centrals, but I am surprised that they would want to decrease pressure if they had more Hypopnes........maybe I have been totally wrong all these years in my assumption that Hypopneas should decrease with more pressure????
Resperonics Titration Flow Chart:
Also interesting to me is that my Transcend Auto also does not want to increase pressure above about 12.5 if I leave the high end open, so it's a little baffling to me that both the Algorithm on the F&P Auto and the Transcend Algorithm don't want to go higher than the 12cm range, but both my ResMed machines want to keep going up in pressure close to 15cm.......I didn't think there would be that much difference in these different brands of machines and their respective Algorithms. Just something to be aware of with different brand machines if you ever switch.
So anyway what is your take on the Hypopneas increasing with therapy pressure rather than decreasing??????? <scratching my head on this issue>
