So many questions! I am two nights into using CPAP. I was diagnosed at a hospital in the UK with 'moderate' sleep apnea, and an AHI score of 21 from a home sleep test. I originally went into hospital regarding a blocked nose which a scan revealed was a deviated septum and allergic rhinitis. They referred me to the sleep clinic at the hospital. I am male, in my mid-30s, average weight, certainly not overweight, a non-smoker and non-drinker.
The first night on CPAP (full mask, Resmed autoset Airsense 10), my average AHI was 3.2 events.
My question: Is there a chance my sleep test could have been wrong? It was done over one night and by pure chance was a night I suffered huge stomach cramps, felt dizzy and sick with suspected food poisoning, barely slept a wink, up and down all night!
PS: It's great to find this forum and fellow CPAP users.
Hi FrankFrog,
It might be better to ask if sleep tests can ever be right.
There are too many variables and we are all individuals and we are human.
If you took a test on another night or with another clinic or in another state or country the results would be different.
Just how different is the big question.
Another question might be how different would it need to be to make a difference to the outcomes and options?
Views may differ, but my view is that a home sleep study underestimates the AHI compared to a in lab overnight sleep study. The reason is simple. AHI is calculated by dividing the total number of apnea and hypopnea events over the night by the hours. In a lab test, they know when you are asleep, so the denominator is sleep hours. In a home test, they only know time in bed or machine on time. That will always be longer, and sometimes much longer if you had a poor sleep.
Home Sleep Studies Underestimate AHI
On your AHI of 3.2 do you know how much of that was central or clear airway compared to obstructive or hypopnea?
Have a look at the other thread started by someone else from the UK. I posted some links there on a manual for your machine, and to SleepyHead.
With home studies, a big factor is exactly what kind of equipment they used. Some home study sets only have 3 sensors in them, which leads to much less reliable data. Others have almost as much as a full in-lab study, so they are much more reliable.
One individual will experience some variation in their breathing from one night to the next, but all the data strongly suggests that it's pretty minor. Also remember the scientific rule of thumb - if you see a thing then it is there, but if you don't see it doesn't mean that it's not there, it just means you didn't see it. So, if you have a good quality sleep study with proper equipment and they record you having obstructive events, then there is little doubt that you do have OSA because there is an actual recording of it happening. If a study doesn't find anything, then it's always possible there is a problem and it just wasn't detected for some reason.
In my experience, home studies are more likely to over estimate AHI than under estimate it. It is certainly not the case that all of them use time in bed as opposed to total seep time. That is very much dependant on the specific system. Although most of my work is in a lab, I also use a home study setup regularly and it certainly uses total sleep time, as we record 4 channel of EEG to measure sleep stage, so we know when you are sleeping and we know when you're awake (we know if you've been bad or good so be good for goodness sake...).
Perhaps try to get a look at the original data, or have a second study and see how it compares.
As a point of disambiguation, the 3.2 number you were seeing on your machine’s sleep report was likely your residual AHI, I.e., the apneas and hypopneas that remained despite or AFTER treatment. And that number isn’t too bad. The AHI of 21 was probably the average through the whole night without treatment. Those numbers are in no way contradictory or inconsistent. So, if that’s the reason you are questioning the test results, I think you can relax. But if it is for some other reason, let the folks here know.
It’s also important to note the difference between your AHIs during REM and nonREM Sleep, which can be very different, plus your O2 desat levels. For example, I had an average AHI of 19, but obstructed 83 times an hour during REM Sleep (when I could even get into REM sleep, which wasn’t often. There was an overlooked clue:from puberty on, I never remembered dreaming, but the reality is, I WASN’T dreaming, because I coildn’t remain in REM sleep.
I would also regularly desaturate below 60, which is life threatening and very hard on your cardiovascular system. It also kills beta cells and leads to DM2. And I awoke every night after 3.5 hours of sleep, unable to stay asleep or get back to sleep, because in REM, my body had to choose between sleeping and breathing. Fortunately for me, it chose breathing. Some people aren’t so lucky.
Some people desaturate very badly and suffer life threatening consequences from the hypoxia. Other people suffer more from the sleep fragmentation and respiratory arousals. There are many different subtypes of Sleep Apnea and many co-morbidities.
Congratulations on getting diagnosed. Most people suffering from sleep apnea remain undiagnosed, and will have a miserable quality of life. and many will die prematurely, never knowing what was wrong, or having had a chance to treat it. You have the chance to beat that rap.
Treatment IS worthwhile. Hang in there and fight for your health and well being!
Thanks for all good comments here. This is copied from my comment on: "Could it be sleep Apnea?"
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Jeff...Houston
