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AHI rises through the night


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I use a CPAP machine and it's great, though of course annoying too. Not so long ago, I learned how to activate the clinical menu so I could see all the info that the manufacturer thinks patients are too dumb to use. I sleep well, but almost never for 8 hours. I get restless and wake up and struggle to go back to sleep. Looking at the data on the machine, my AHI (apnea/hypoapnea index) seems to go up the longer I sleep. This is a pretty consistent result. I think when it gets too high, say, over 5, I wake up. Anyone know what causes this and what to do about it?

It seems to help a little bit to take a very small amount of dexedrine in the middle of the night. (I take this stuff for ADD in the daytime.) I'm thinking maybe I get congested a bit as the stuff wears off through the night. I also take clonidine, which helps me sleep, but it doesn't seem to affect the AHI issue.

Any thoughts?

Thanks!

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I'm having a shitty night and can probably provide a better answer on this one after I've had some sleep. But I don't want to leave it totally unanswered.

Heh, I think the manufacturers want to keep people out of the clinical menu's because you can end up changing the pressure on the machine, and the machines are usually set to whatever your doctor wrote the prescription for.

Okay here's the short story. You cycle through stages of sleep over and over through the night. As the night goes on, you spend more and more time in the REM stage of sleep. REM sleep is notorious for making respiratory events worse.

That's one example of something that can cause your AHI to rise as the night goes by.

There are other possible causes and many possible solutions.

If you don't mine me asking, I have some questions:

How long have you been using the CPAP machine?

How long ago was your last sleep test?

What degree of apnea were you diagnosed with?

Even on a CPAP there are usually a few apneas or hypopneas

Did you have a full night sleep study while using the CPAP machine before you got it?

What type of machine are you using?

What style of mask are you using?

Have you gained weight since you got the machine?

Feel free to ignore me if any of these questions are too personal.

~ May

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That makes a lot of sense about the REM. Some snippage in the following:

snip

If you don't mine me asking, I have some questions:

How long have you been using the CPAP machine?

a bit over a year

How long ago was your last sleep test?

ditto

What degree of apnea were you diagnosed with?

severe

Did you have a full night sleep study while using the CPAP machine before you got it?

I was on a late schedule, so I only got about 5 hours in. That made me feel a lot better than 8 hours of what I had been getting.

What type of machine are you using?

Resmed Elite II with a humidifier. I've got it set for that feature where it backs off on the pressure automatically when you exhale. I forget the acronym for it. This isn't to help me sleep better, just helps me not to swallow so much air.

What style of mask are you using?

the kind that covers my nose and my mouth too. The nose only kind irritated me just below my nose. Mustache might have had something to do with it, plus I thought it would be nice to have something I could use if I got the sniffles. However, the machine seems to keep colds at bay. Maybe that's the humidifier part.

Have you gained weight since you got the machine?

no

Those questions aren't too personal, they're very relevant.

I'm not too badly off right now, but I have this fantasy that someday I won't have a little edge of fatigue at all times. Of course, I'm thinking that could be an ADD thing.

Seems like you know a lot about this stuff.

Thanks

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BTW, what's so horrible about changing the pressure, other than a bit of air in my stomach? How am I supposed to inflate my air mattress properly? ;-)

I think I have a less than properly reverent attitude about these devices. I even made my own to use while the wheels of bureaucracy were turning. Of course I only achieved one that worked well about a week before I got the commercial one, mine didn't have a humidifier, and it was noisy enough that I used a twenty foot long hose. Nor does it have the back off when exhaling feature. But it works. I keep it in the car for naps.

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If the person running your test had half a brain, 5 hours is usually sufficient.

The setting is probably EPR - expiratory pressure relief. It's usually a good thing since people sometimes find it difficult to exhale against a constant pressure and that feature adjusts the pressure to make it a bit more like "natural" breathing.

A humidifier is usually a beautiful thing.

A nose that covers both your nose and mouth is called a full face mask. There are a lot of different styles of them, as there are many different styles of nasal (nose only) masks. One concern with a full face mask is that they are one of the hardest masks to fit properly. They have a tendency to leak. In a system that requires air to be at a specific pressure to be effective, air leaks are a bad thing. If the leak gets high enough you won't be getting the full benefit of the pressure because the leak will lower the actual amount of pressure that you are receiving. One reason why they are so hard to fit is because the muscles in your face change during the night as your body relaxes. What fits you well when you are awake is not necessarily doing so all night long - again especially in REM sleep because your muscles tend to relax the most in that stage. Also, a mustache tends to make full face masks harder to fit because it gets in the way of the mask making a proper seal against your face. The nasal pillow style masks are usually the easiest ones when someone has facial hair - but at the end of the day it's about whatever you are comfortable enough wearing to get some sleep. It's just imperative that whatever mask you are using is fitting you properly throughout the night.

Most machines can measure leak through the night. If your machine has a chip in it that's recording the data it's the kind of thing that your physician can download and see if that's what the problem is.

If your apnea is severe, your pressure might be at the high end.

Actually if you got into the clinician's menu - you probably know what your pressure is. If so, I'm curious to know where they have you at.

Do you know if you had your sleep test in an accredited lab? There are standards of the AASM that have to be followed in the use of positive airway pressure treatment that accredited labs have to follow. Non accredited labs aren't required to stick to the same rules.

So some thoughts:

Because your sleep study was only five hours - you could have been titrated to a pressure high enough to improve the first five hours of your sleep but not high enough to be taking care of the rest of the night - which could account for the higher AHI during the last few hours of your sleep. Those hours weren't caught on the original sleep test and your pressure might be incorrect.

The problem with changing your pressure yourself is because ideally everyone has a "sweet spot". Sleep apnea should be treated with the lowest possible pressure that will minimize respiratory events. The problem with randomly raising it is that once you go too far over that sweet spot what happens is that respiratory events INCREASE. Events of obstructive apnea treated with too high of a pressure can become events of central apnea.

No weight changes is good - then that's probably not part of it. Changes in other things like (for example) medication, alcohol consumption and allergies can also change the degree of your apnea.

If you have insurance - getting another sleep test would be lovely. Personal opinion, the procedure for sleep tests is somewhat lacking. It's hard to get you titrated to a correct pressure when you're in a strange place and sleeping with this mask on your face for the first time. Once you're used to sleeping with a mask, it's often easier because at least you're used to the pressure and it's easier to run you through a variety of different pressure so that the doctor has that much more information to look at to use to decide what pressure was the best one for you.

Insurance (if you have it) will usually cover re-titration studies more often then people realize they will. They will also cover new masks (usually) every six months. It's one of those things that they won't tell you. You have to push for it. If you have the option, it's usually worth it to harass them. As time goes by they are making PAP machines better and better and new styles of masks are always coming out.

Some areas have apnea support groups - which are great places for (free) information. Often times they are run by people that have apnea themselves and/or work for some of the mask distribution companies. They usually have a wealth of practical information about masks and machines and tips on how to best use them.

http://www.sleepapnea.org/awake/index.html

Heh, yeah I can carry on for a while about this stuff. I ran sleep studies for five years. The AWAKE groups are pretty good for free information. I've sat in on a few meeting for continuing education credits. I've seen a lot of people bring in their masks and machines and get some good advice on how to best use them. I've also seen some of the people that work for the distribution companies bring in sample masks and let people try some of them on. Unfortunately - the options you're usually given during the initial test are limited to what that particular lab has in stock and some labs stock WAY better then others so sometimes there are things out there that could work much better for you that you don't even know about.

~ May

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some snippage below

If the person running your test had half a brain, 5 hours is usually sufficient.

The setting is probably EPR - expiratory pressure relief. It's usually a good thing since people sometimes find it difficult to exhale against a constant pressure and that feature adjusts the pressure to make it a bit more like "natural" breathing.

5 hours was the second test. First test was shorter and intervals only.

Yup, EPR sounds right. For me, it only prevents ingesting air. I don't have a problem exhaling against pressure, or inhaling against resistance. I think my breathing is fairly insensitive. I once sucked out all the usable air in a SCUBA tank against the drag of the reserve valve. Fortunately, no obstructions were between me and the surface. Sometimes I don't wake up for a while when the CPAP hose falls off. Or at least I think it goes on for a while, but then of course I'm gasping.

Most machines can measure leak through the night. If your machine has a chip in it that's recording the data it's the kind of thing that your physician can download and see if that's what the problem is.

If your apnea is severe, your pressure might be at the high end.

Actually if you got into the clinician's menu - you probably know what your pressure is. If so, I'm curious to know where they have you at.

They put it at 9 because I said 10 made me uncomfortable, even though they said that worked better. I've set it to 10 now after a bit of experience.

Thanks for all your information!

The data I can access myself resets every day at noon, so I can't tell you right now what leakage I've been having. I seem to remember 0.3, or was that 0.03, in liters per something. What's an acceptable rate? My impression is that it's not a problem. I seem to remember that the leakage varies a lot, percentagewise, and is not correlated with the AHI problem, but that's just an impression.

Do you know if you had your sleep test in an accredited lab? There are standards of the AASM that have to be followed in the use of positive airway pressure treatment that accredited labs have to follow. Non accredited labs aren't required to stick to the same rules.

If they're accredited, I didn't see it on their web page. However, they're in a good hospital, and really seemed to know what they were doing. Even if they sent me to the cafeteria in the morning with a head full of glue. Seemed like the other customers were edging away from me.

So some thoughts:

Because your sleep study was only five hours - you could have been titrated to a pressure high enough to improve the first five hours of your sleep but not high enough to be taking care of the rest of the night - which could account for the higher AHI during the last few hours of your sleep. Those hours weren't caught on the original sleep test and your pressure might be incorrect.

The problem with changing your pressure yourself is because ideally everyone has a "sweet spot". Sleep apnea should be treated with the lowest possible pressure that will minimize respiratory events. The problem with randomly raising it is that once you go too far over that sweet spot what happens is that respiratory events INCREASE. Events of obstructive apnea treated with too high of a pressure can become events of central apnea.

I tried going to 12, but it didn't seem to make a definite difference, and I started ingesting air again.

No weight changes is good - then that's probably not part of it. Changes in other things like (for example) medication, alcohol consumption and allergies can also change the degree of your apnea.

I think the only really big change was getting the data. What alarms me is that if I start the night averaging 2 or 3, and I end the night averaging 5 or 6, it must have been a lot higher than that toward the end.

If you have insurance - getting another sleep test would be lovely. Personal opinion, the procedure for sleep tests is somewhat lacking. It's hard to get you titrated to a correct pressure when you're in a strange place and sleeping with this mask on your face for the first time. Once you're used to sleeping with a mask, it's often easier because at least you're used to the pressure and it's easier to run you through a variety of different pressure so that the doctor has that much more information to look at to use to decide what pressure was the best one for you.

I've been hesitant to go for another study because it seems SO fancy and expensive and my problem isn't all THAT bad.

I think my mask is pretty good, but will check the leak rate. My mask still seems to be pretty good, though my first hose wore out. The medical supply company never hesitates to remind me what I can get. They seem greedy, even. My only complaint about the current machine is the noise. It's not really very noisy but I find I prefer earplugs anyway, even if they don't block the noise inside the hose.

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P.S. Another theory:

My breathing tends to be quite slow even when I'm awake. Although I don't think this is the explanation, maybe it gets a little slower after I've been asleep for a while? I seem to remember trying to time it and finding that it was pretty close to the definition of hypoapnea when I was awake and very relaxed. I seem to recall an inhalation and an exhalation could add up to as much as 12 seconds or so, though sitting here at my desk it's more like 6. The reason I don't think this is it is because I seem to wake up earlier than I want when the AHI is a high number. On the other hand, it's almost always the hypoapnea component that causes the great majority of the rise in the AHI.

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