Flow Limit and EPR?

[GuyScharf]

I decided to change from EPR 3 to EPR 2 to see how that would affect how I felt and maybe CAI vs HI--those two being the primary component of AHI for me.  So far, so good, but it will take more time to see whether the change results in a statistical difference.  I'm also watching for aerophagia.

However, I am noticing that 95% Flow Limit measure has apparently increased, and the flow limit graph appears denser.  Is this to be expected?

I would have thought that reducing EPR, without changing pressure, would increase EPAP and reduce the flow limits rather than increase them.

I'd appreciate education on the expected relationship between EPR and flow limits.

[Gideon]

Consider EPR as the same thing as PS on a BiLevel. For therapy, you always want to think of its effect on EPAP and sometimes we alter pressure to have the effect on EPAP that we want, frequently to keep EPAP the same. PS is what you use to treat Flow Limits. (and RERAs, Hypopneas, UARS. )
So lowering EPR will in general INCREASE the above somewhat, though an increase in EPAP could tend to reduce them. Increasing EPAP is most effective against Obstructive Apnea. Frequently the reason we reduce EPR is just to reduce Central Apnea that is induced by flushing too much CO2 out of the system.

[GuyScharf]

So, with my Autoset, if my goal is to reduce CAI without increasing HI, should I try lowering pressure by 1 when I decrease EPR by 1?

Last month, with EPR=3, I changed pressure from 9.8 to 10.2. For the last year, my AHI/OI/HI/CAI numbers averaged 1.63/0.14/0.84/0.63. For last month, with pressure at 10.2, the numbers were 1.66/0.10/0.71/0.83. So increasing the pressure by 0.4, without changing anything else, seems to have decreased HI and increased CAI.

I am trying to fine tune my results and see if any change results in feeling more rested when I wake up. I know my AHI is low enough that it might not be worth bothering about, but wanted to see if changing up the settings might improve feeling tired in the morning.

[Crimson Nape]

You are correct, Sir! This will maintain the same EPAP pressure while lowering your IPAP. This is another, although slight, difference between using EPR versus a true Bi-level machine. You can only adjust the EPR in 1 cm increments as opposed to .2 cm increments on a Bi-level with PS. Until you mention the .4 cm setting, it never occurred to me of this difference.

[Gideon]

Did that answer your question Guy?

On a BiLevel you can set EPAP to the machine min (4) add PS (3) and no problem IPAP is 7
On a CPAP you can set Pressure to the machine to the machine Min (4) add EPR (3) and you still have 4 because you cannot go below the machines min.
Thus Min Pressure = 4 (machine min) + EPR (3) = 7, For EPR=2: Min Pressure = 4 (machine min) + EPR (2) = 6 thus getting the fully defined amount of EPR all the time.

[GuyScharf]

Yes, I know about the minimum pressure of 4 and how that might affect actual pressures. My pressure won't be low enough for that to be an issue.

My original study suggested CPAP with a pressure of 13 cmH2O. Since I got an APAP machine instead of CPAP, I've never set the minimum pressure that high, figuring the APAP would drive it up there as needed (and it does, usually two or three times a night, after which it drops back to the set pressure).