Same AHI at low and high pressures

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abagail
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Same AHI at low and high pressures

Post by abagail » Sun Nov 23, 2014 3:00 am

Hi All, so I am a bit confused. I am new to CPAP, I've been using it for about a month now.

My prescription was for 6-16 to then see how that went and possibly narrow down on a single pressure (I'm currently hiring a machine, and it is much cheaper to buy a straight CPAP here, however I'm thinking I might import the machine I am hiring from the US).

I initially had no real problems adjusting to CPAP - I could wear the mask the whole night etc, however a month in, I noticed I was gassy and I was still waking up during the night more than normal. A few nights I also had issues where the pressure had gone up to the maximum and the mask leaked like crazy and I had to stop, adjust and start again.

My AHI had been ~0.4 from the very start of using CPAP - so I thought I'd try a couple of nights of lowering the pressure to see if this would make it more comfortable - expecting it to increase my events.

So I've spent a few nights now with a 4-4 pressure (I found it quite comfortable to breathe at) - and my AHI was basically exactly the same ~0.4 - I still had 2-4 OA towards the end of the night, just like the nights where I had the higher pressure. The funny thing is, this was never when the machine increased the pressure, there was always a lump earlier in the night.

From my sleep study they would have prescribed a straight pressure of 10 apparently - I had a only 2 OA, but a number of Hypos during the night as they titrated me.

I'm a little confused by the whole thing really - is it normal to have the same AHI at low and higher pressures? Huh

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kteague
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Re: Same AHI at low and high pressures

Post by kteague » Sun Nov 23, 2014 4:25 am

I'm wondering if leaks caused your pressure to go high attempting to offset the leaks, or if the pressure going high caused the leaks. Can't even venture a guess. Maybe your detailed data could give some clues. Sounds like there's a few things for you to sort through. For starters, if your data shows you never need anywhere near the 16 to handle events, you could put a limit that doesn't let it go so high. If it is chasing leaks, that would help it not take that futile pursuit. Unnecessarily high pressures are more likely to be problematic with leaks and air in the belly. If your sleep study said you need a pressure of 10, I would probably try capping it off around 12 and watching the data for a few nights. If your leaks are controlled and you're never getting near the upper limit, you could drop it closer to whatever proves to be your actual needs. I would be hesitant to place a limit below the titrated pressure of 10 without more detailed data over a longer period of time to substantiate that decision. The chances of you only needing 4 ever is highly unlikely. Stranger things have happened, but I'd feel safer if the machine was set to allow it to use more pressure if needed. I mean, what if your night at 4 with good results you never slept on your back during REM, which is generally the worst case scenario for events. Then on another night you did roll onto your back during REM, your events worsened, and your machine was unable to meet your changing needs. If your detailed data over the course of several nights happens to show you stay pretty much at one pressure, you may decide it is easier and more cost effective to go ahead and use a fixed pressure machine. Data will be your friend in the decisions you will be making. Knowing your AHI is a good place to start, but is not enough to help you make well informed decisions. If you don't already know how to get your data, I'm sure someone will come along and let you know the process. Best wishes.

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Julie
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Re: Same AHI at low and high pressures

Post by Julie » Sun Nov 23, 2014 5:27 am

Maybe you just don't have OSA, but when on your back do register a few events. And some hypopneas. And if you don't back sleep, maybe you'll feel better (in a reasonably short time). See the posting here "Hope and sharing a possible solution..."

abagail
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Re: Same AHI at low and high pressures

Post by abagail » Sun Nov 23, 2014 5:34 am

Thanks for the reply kteague. Looking at my graphs - It appears that the leaks were caused by the high pressure as they didn't start till after the pressure got so high.

I have slept for 5 nights now with the same low AHI at a pressure of 4.

My data had some common patterns - there was some peaks in the flow limitations graph around the time that the machine would usually raise the pressure - sometimes sky high - but never any apneas. I'm not sure If this is when I typically go into REM sleep, or maybe I am rolling onto my back (I start as a side sleeper) or something. My apneas are usually later in the night - and were generally around the same time when I had the pressure set at the doctors prescription (initally set at 6-16 for now, expected to end up ~10) and when I have set the pressure 4-4.

two nights set at 4-4

Image

Image

Typical nights a 6-16

Image

Image

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Pugsy
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Re: Same AHI at low and high pressures

Post by Pugsy » Sun Nov 23, 2014 12:43 pm

Curious question...what was your AHI pre cpap therapy?

You know it isn't impossible that 4 cm simply does a good job keeping the airway open.
If you are sleeping well and feeling decent during the day the I wouldn't worry about what pressure number you use.

Snores and flow limitations are part of what drives the pressure up...and not all snores or flow limitations will grow up to be full grown apneas or hyponeas worthy of a flag.
Obviously even with a pressure of 4 being used they still don't grow up to be full fledged OAs or hyponeas.
The flow limitation line when 4 cm is use isn't horrible looking either.

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abagail
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Re: Same AHI at low and high pressures

Post by abagail » Wed Nov 26, 2014 3:15 am

Thanks Pugsy - My AHI from my original sleep study where I was diagnosed was ~10 (so not horrible). I was just one cluster of a heap of hypopneas.The lowest O2 level was 95% - average of 97%. During the study I remember the tech coming in and putting the tube thingy back in my nose as it had come loose. I have asked multiple times whether that interfered with the results, and they never answered - now I'm wondering If maybe I've been misdiagnosed. Unfortunately I have no idea if the time this happened correlates with the end of the cluster. They did pick up a large amount of spontaneous arousals 20/hr in addition to the hypopneas - which were greatly reduced on my study with CPAP - I'm not sure why as these arent supposed to be breathing related (Im going to ask my sleep doc at my next appt on monday)

I was already sleeping well prior to CPAP, but generally fatigued during the day - but I don't fall asleep/nap. This fatigue has not gotten any better on cpap despite my very low AHI and good compliance (I do know some people say it takes a long time). The other factor is that I am on medication that has fatigue as a side effect, and my fatigue has gotten noticeably worse as my dose has increased - so it may have nothing to do with sleep apnea. I originally got tested due to chronic headaches and they have not improved at all.

I do snore - however no one has ever noticed me stop breathing. According to the machine most of the events are 10 seconds - I think the longest has been 16 seconds, but that was a one-off. I do have a messed up nose which may explain the snoring - I had a mucocele in a turbinate which had to be removed, so I am left with a deviated septum and stuff got shifted around a bit.

I'm happy to keep going with the cpap if it's helping me, but I dont want the expense and discomfort if I've been misdiagnosed. I suspect my sleep doc is not going to be all that helpful. Even before the cpap study, he presented all the treatment options (including surgery) but stressed I could do nothing if I wanted to. It was almost like he was pushing me more to doing nothing he stressed it that much, he did say he recommended doing a cpap trial, but didn't tell me anything about the risks of not treating it or anything (I already know, but he didn't know that).

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