A Question about Pressure

I've been slowly increasing the minimum pressure on my Dreamstation since last year. It's going OK--I rarely have and AHI that's more than 1.00 and I feel good--but after a while at a given pressure setting, I notice that I wake up more often during the night and Sleepyhead will show increases in hypopneas and clear airway events. That's when I increase minimum pressure by a half a degree. I have to take it slowly or I have problems with gas, etc. Anyway, I recently made an increase in minimum pressure from 7 to 7.5 and a max of 10. When I lookedat Sleepyhead for last night, it says that my "Average Pressure" was 7.65 and "90% Pressure" is 8.10. This tells me that it was a good thing that I increased minimum pressure, but If 90% Pressure is 8.10, why isn't the Average Pressure higher? I'm trying to make sense of this and get an idea of how high I may ultimately need to set the pressure on my machine. Last night my AHI was .62 and I had 4 hypopneas, 4 flow limitations, and one clear airway event, but I felt like I slept pretty well--8 hours--and only woke up a couple of times.

The 90% means 90% or less - up to 90%. It does not mean 90% most of the time.

And is there is a reason your high setting is so (relatively) low?

Just curious if you normally sleep mostly on your back... that could be setting off more events, at least the hypopneas.

Jeanne Ellen wrote:If 90% Pressure is 8.10, why isn't the Average Pressure higher? I'm trying to make sense of this and get an idea of how high I may ultimately need to set the pressure on my machine. .

Because they have virtually nothing to do with each other.

Neither of those numbers tells you what was happening during the night, only the pressure graph does that.

http://adventures-in-hosehead-land.blog ... de-to.html

The definition of 90 % of anything (pressure or leaks) is where we were AT OR BELOW for 90% of the night.
The "or below" part is very important and often over looked or forgotten and people think it is where we were at for 90% of the night.
It is easily skewed higher my just a relatively short period of time at higher pressures.

OK, thanks for the "at below" explanation, Pugsy, I get it now.

As to why my maximum setting is so low, I guess it's a reaction to what happened when I first started cpap and my doctor set the machine at min 8 max 12, which was more than I could tolerate. After I gave up for a couple of weeks, he decided to set it at 6 on regular pap and there it stayed for almost 6 months, until I decided to try autopap again, this time with cflex at 3. So I've been inching up slowly and cautiously ever since. I guess I could try to increase max to 11 and see what it feels like.

I always start out sleeping on my side and mostly turn side-to-side during the night. Sometimes I do wake up on my back, so I'm sure that's part of my waking-up problem. I'm not sure that increased pressure would take care of this, from what I read.

Setting the higher pressure even at 15 won't affect e.g. your aerophagia, but will let the odd high event level out where it needs to rather than being constrained. The low setting's the one that counts re effective therapy. I wonder if you'd feel better with a lower flex setting however... it can also make your AHI #'s a bit higher, so you need to find a balance.

I don't want to do more than one thing at a time, so maybe I'll just raise the max a bit. I guess I don't really understand cflex. I thought the cflex setting at 3 would reduce the pressure when you exhaled more than 1. Is it the other way around? Maybe I'm not "grokking" this. Which is entirely possible.

You're correct - I just wasn't sure if you understood the feature well. But don't be so careful about the max setting, it's not like when you oh-so-carefully raise the min. pressure in little increments - you can open it wide without much effect at all... the only one being that IF your pressure needs to go higher at some point, it'll have where to go and not be cut off.

OK, thanks for the clarification. I'll take it up a notch tonight and if all goes well, I'll take it up another notch the following night. Who knows, maybe at some point I'll be back to where I started a year ago.

Jeanne Ellen wrote: I guess I don't really understand cflex. I thought the cflex setting at 3 would reduce the pressure when you exhaled more than 1. Is it the other way around?

The higher the Flex setting the greater the exhale relief or drop in pressure from inhale.
Now Respironics Flex (C Flex or A Flex) amount of reduction is flow based and not a straight linear 1 cm per setting reduction like the ResMed machines.
Instead the Respironics machines will reduce the pressure on exhale based on your own breathing force and rate.
People that breathe more shallowly and less forcefully may not get the full reduction offered at the setting that have chosen.

Flex relief...setting of 3 ...the maximum drop during exhale is 2 cm...not 3 cm...and a person may or may not get that full 2 cm drop depending on how forcefully they breathe..

I tell people to pick a setting that feels good if they want to use it (or turn if off if off actually feels better) and use the setting that feels the best regardless of the number.

Also..Flex relief won't even kick in unless the machine is using 6 cm or higher pressure.
If someone is using 5.5 cm...and they have the Flex turned on...it won't even work or reduce anything until the pressure of 6 or higher is reached.