It’s important to remember that your CPAP machine is a delicate, finely tuned medical instrument that tracks and delivers essential health data to help you and your clinicians provide you with the best therapy that you can have.
With that in mind, it’s good practice for you as the patient, to be able to take some responsibility for your own health, wellness and treatment by understanding what those numbers actually mean, which data is critical, and under what circumstances are some numbers less relevant.
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CPAP is About Feeling Better
One thing that often gets overlooked in the entire process of trying to treat your sleep apnea is that the critical goal is to improve your quality of life so that you feel better.
For long term sufferers of obstructive sleep apnea (OSA), you know firsthand how those symptoms over time can seriously erode your standard of living – waking up feeling exhausted, having micro-
These are all common symptoms of OSA that destroy your quality of life.
Absolutely, there are highlight problems that OSA can cause like long term heart damage, elevated blood pressure and weight gain, but on a day-to-day basis, it’s the little things that hurt your standard of living the most.
And that’s the critical thing about CPAP is that when the therapy is working and dialled in, those symptoms diminish significantly.
I can tell you from my own experience that the very first night I used a CPAP machine, it was like all the colours of the world were sharper and the Sun just felt like it was brighter. I felt like I was on speed because every single thought I had was coming to me more quickly with razor-sharp clarity of purpose.
It was life-altering, and I didn’t know what my AHI was that night, what pressure the machine was running at or how my leaks were – I just felt amazing.
Remember that, be in touch with how you feel and don’t let the data distract you from being in touch with your body.
AHI – The Most Important CPAP Metric
While we’ve talked about the need to be in touch with how your body feels, that’s not to say that all of the data is irrelevant because that would be rather silly.
Your Apnea-Hypopnea Index (AHI) score is the one data point that in many respects summarises how your breathing performed while you slept, so that’s pretty important in the context of understanding how well the CPAP therapy is working for you.
Let’s start with a quick definition of what Apneas and Hypopneas are:
Apneas are pauses in your breathing while you sleep
Hypopneas are periods of shallow breathing during sleep
These numbers are then combined to give you an AHI score that tallies up the number of total episodes that you have per hour averaged across the period of sleep.
If you have been diagnosed with sleep apnea, then you’re probably already familiar with what those averages mean, but to focus the conversation –
“Normal” sleep for someone
AHI / Sleep Apnea Score Values
|AHI Score||Sleep Apnea Severity|
|Less than 5||“Normal” Sleep Behaviour|
|5 – 10||Mild Sleep Apnea|
|10 – 15||Moderate Sleep Apnea|
|Greater than 15||Severe Sleep Apnea|
Your clinicians may give you different interpretations, and you should always listen to them.
I know that when I was starting my CPAP therapy, my diagnosed AHI was 72 so my sleep doctor was working on getting my AHI down below 15 and on making me comfortable wearing the mask with certain air pressures.
I was lucky, I took to the full face mask instantly, and after a few sessions with the doctor adjusting the starting pressure and the sleep techs making some adjustments to my mask, my AHI was down below 5 in less than a month.
At this point, I check my AHI probably once a week or if I don’t feel like I slept well one night. For the most part, on my particular CPAP Machine (the F&P Icon+), I can see what my 7-day AHI average has been, and that’s the number I look at for
But having said that, if I feel good and am not waking up tired or feeling like I need a nap during the day, I might not check my AHI or any other metrics for weeks at a time.
The thing to remember is if you’re not feeling good when you wake up, check your AHI to see how you slept – that’s the first place to look.
Pressure – How Much Air is Being Forced Into You
The pressure that your CPAP machine is set to
To start with, CPAP pressure is measured in a strange number, even for those of us who grew up with the Metric system, cmH2O.
Effectively, cmH2O is a measure of how much pneumatic air pressure is required to raise water in a manometer as measured in centimetres.
Did you get that?
The easiest way to think about it is that cmH20 is a precise, standard measurement for low-pressure air ventilation so that machines can be adjusted to administer the right air pressure in a finely tuned way.
As a CPAP user, it’s important to know that the higher the number, the higher the air pressure the machine is running into your airways to keep them clear.
Most CPAP machines available commercially do between 2 and 20 cmH2O.
What makes this a bit more confusing for the average person is that the CPAP machines have become increasingly intelligent over the last decade.
CPAP machines now have features that can “ramp” up your pressure to make it easier for you to adjust to at the beginning of your sleep session while “automatic” machines can intelligently adjust your pressure up and down automatically based on your current AHI pattern while you sleep.
So if you’re breathing pauses or becomes shallow, an automatic CPAP machine will start ratcheting up the pressure to normalise your breathing and once stable, it will lower the pressure back towards your baseline level set by your clinician.
The important number that you need to know is what your baseline pressure level is.
When you’re first starting out with CPAP, it’s very likely that your doctor will keep this number a bit lower to see how you respond. They’ll look at your sleep data and see if they need to adjust it over time until you get to your best baseline pressure.
If you invest in an automatic machine, this process becomes a bit easier, and the data is a bit better – your doctor will see what pressure the machine moves you to during the night based on your apneas and hypopneas and they can adjust it accordingly.
From personal experience, my doctor set my pressure initially to 6, and after the first month, he increased it to 8.
My nightly average pressure was on or around 10, which means that the machine worked out that my AHI was best controlled with 10 cmH2O of pressure and very rarely dipped below that with the occasional spike up into the teens.
I can handle higher pressures on my CPAP just fine and I’m a naughty CPAP patient, so I entered clinician mode on my CPAP machine and changed my baseline pressure to 10.
I don’t recommend you do this – let your doctor deal with these things and tell them if you feel you would like some of the settings changed. My sleep doctor just shakes his head when he sees my reports and says if I’m comfortable and the AHI is fine, then that’s what matters.
Again, knowing your baseline pressure is essential and if you have an automatic CPAP machine, understanding how your pressure changes throughout the night is something that can help you have a meaningful discussion with your sleep clinician about your therapy.
CPAP Mask Leaks – Managing The Problem
The first thing I always say to people who are new to CPAP therapy is that your CPAP machine will show some leaks in the data.
Your mask has ventilation which acts as an exhaust and that registers as a leak.
In fact, if you can get the specification sheet for your mask, you’ll see that it’s rated for a certain level of leakage – most full face masks have a leakage level between 20-35L/minute.
Here’s a secret – I’ve tried dozens of full face masks over the years because I like to test them and NEVER had I had a mask register below a 40L/minute leak level.
In fact, my current Simplus mask leaks at about 52L/minute over the last 30 days and that’s with a new cushion and headgear that I purchased just in the past two months.
But my AHI over the past 30 days is 0.9, so the leaks aren’t really impacting me.
This is where the correlation of the data points we’ve discussed so far is significant.
If your AHI is high and you’re using an automatic machine, the air pressure being pushed through to you will be increased to try and correct your breathing.
This increased pressure may generate so much additional force that depending on your sleeping position at the time, how your mask is currently sitting on your face and the tension of the straps, you might get leaks.
In situations like this, in your sleep data, you will see an increase in AHI, an increase in pressure, and a simultaneous increase in leaks.
Before going on, it’s important to note, that if these leaks aren’t waking you up and your sleep data shows your breathing normalise then this is an issue that you should take up with your clinicians, but I wouldn’t recommend you doing anything yourself.
Remember, CPAP therapy is about feeling better! If a leak metric goes up, but you still feel good in the morning, and the leak itself isn’t waking you up, then it’s not super important, just bring it up the next time you speak with your sleep technician or your doctor.
If the leaks are waking you up because they are blowing air in your eyes (I hate that) or they’re making noise – then you can try some simple adjustments of the placement of the mask on your face or of the tightness of your straps.
When leaks become a problem to the point where they’re interrupting your sleep, then you need to go see your sleep technicians to see if maybe the mask needs some adjustments, if your machine needs to have the pressure settings changed or if perhaps you just need to try a whole new mask.
The therapy is designed to help you sleep better, and if it’s waking you up or causing you to lose more sleep than the benefit you’re getting from it, then you need to do something about it.
Here’s the thing, leak data on its own is not SUPER important. I seldom look at those numbers unless something is wrong. As long as my AHI is low and I feel good, then I leave the leak data to the professionals and just ignore it.
Usage – Being Compliant With Your CPAP Therapy
One number that is tracked by every CPAP machine is your usage.
This is important for people who struggle to deal with having a mask on their face or over their nose because it gives them and their clinicians a benchmark to work towards – if you’re 70% compliant or used the machine for 4 hours a night, then adjustments to therapy can be made to try and increase those numbers.
If you struggle with wearing your mask, then your usage number becomes the most valuable and watched metric with your therapy.
I’ve talked to people over the years who really struggle with usage numbers because they feel that it’s almost like a grade in school – if they don’t use the machine successfully for 5 hours, it’s like they failed.
It’s easy for me to say this because I have had 100% usage compliance since my very first night of using CPAP, but the truth is, you need to remove the emotional element from this number and treat it as an indicator of whether or not you’ve dialled in your CPAP setup.
If your mask isn’t comfortable or the pressure is disturbing you while you sleep, then this isn’t an indictment on you as a person, this just means that you and your sleep team need to keep working to improve the situation, so you get the overall health benefit you started using CPAP to get in the first place.
Don’t let this number intimidate or worry you – it’s 100% there to help your sleep support team (technicians and clinicians) give you the best advice and treatment they can deliver and it’s in no way a reflection on you.
That said, you need to be part of the solution.
Having a plastic mask on your nose or face, sealed to your skin with some silicone and air being pressure forced into your airways isn’t the most natural thing in the world and can take some getting used to.
You are the only person that can do the “getting used to” part – your spouse, your doctor, your sleep technician can all give you encouragement, but the only person who can keep that mask on your face, is you.
And that’s where the usage metrics can become useful – challenge yourself, add a level of gamification to it.
If you’re only using your CPAP machine for 4 hours a night, then challenge yourself to stretch it out to 4.5 hours.
When you have a win, celebrate it. Enjoy the fact that you’ve put your mind to something and you’ve done it.
Like most of the main metrics around CPAP, the usage numbers don’t define your success, they just measure what’s going on.
Additional CPAP Data and Metrics Your Machine May Not Measure
In a clinical setting when your sleep doctor administers your polysomnography (sleep test), they take a variety of other measurements and collect some different data points.
The polysomnography will be looking at:
- Brain wave patterns
- Blood oxygenation levels
- Pulse and Heart Rate
- Eye and leg movements
- Breathing interruptions
With this initial sleep test, the doctors are trying to get a holistic view of your sleep health.
For most people reading this, you probably have obstructive sleep apnea, and what your doctors were looking for during the polysomnography was to see the types of breathing interruptions you were having (apneas vs hypopneas), how long these interruptions where happening for, how often they were happening, were you entering the various stages of REM sleep, what was your heart doing during these episodes and what was your blood oxygenation like during an event.
The results from the polysomnography are much more granular than your CPAP machine will deliver with respect to apnea and hypopnea information for example.
During my test, I learned that for the entire 8 hours, I never once entered REM sleep – that is a pretty severe problem long term.
I also learned that during some of my apnea events, I was not breathing for over 50 seconds and my blood oxygenation levels dropped considerably – again, these are both not good data points.
Mainly, the polysomnography showed that I had severe OSA and was probably suffering from long term sleep deprivation.
They were pretty eye-opening results and it made me grateful that I’d discovered the problem at an early age (I was in my late 30’s) so that any damage was easily reversed, but more importantly, I could manage the problem going forward and lead a healthy life.
These metrics are essential as part of your diagnosis, but on an ongoing basis, concerning your sleep health, they aren’t that important – this is the kind of thing your sleep doctor will want to test your for every couple years to get a picture of your general sleep health.
I know some people who have invested in all sorts of additional health monitoring technology, particularly smartwatches that can monitor your heart rate while you sleep and some can even track your blood oxygenation levels.
Again, for the average person, this seems like a bit of overkill.
If you have your CPAP dialled in and your AHI is pretty good consistently, then all of that other stuff is probably ok too.
By all means, if you’re worried about it, feel free to track it, but sometimes too much information just creates unnecessary anxiety.
Focusing on the Data that Matters
The most important “data point” when it comes to your sleep apnea and CPAP therapy is a “soft” piece of data, it’s how you feel when you wake up and how you feel throughout the day.
You are the only person that is going to be able to measure that.
Let me tell you, over time, when your CPAP therapy is working as it should, you become adjusted to this “new normal”.
For me, it meant I never felt the need to nap – I used to love having a nap for two or three hours on the weekend, but once the CPAP therapy started, I didn’t have a single daytime nap for four years!
In the six years of using CPAP, I’ve had three or four naps during the day and every single time has been when I’m sick.
My new baseline normal is that I’m wide awake and alert for 16-18 hours a day – that’s a data point, if I’m not, I check my sleep data to see if something is wrong with how I slept.
Once you establish that new baseline normal, then you become quite attuned to when it’s not right and that’s when your sleep data from your CPAP machine will come in handy for you.
Your first point of call will be to see if AHI was high the night before and what has it been like for the last week.
Then depending on what your AHI is, you might look at whether your pressure was higher than normal (maybe you were having a high number of breathing interruptions) or if perhaps the mask leaked a bit.
The data is used to colour in the picture for you and help you understand what’s happening.
The biggest mistake that I see people making with their CPAP therapy is that they become slaves to the data.
If their AHI is 3.1 last night and it’s usually 1.8, they panic and think something is wrong with them or worse, they conclude that CPAP isn’t working for them and they give up.
Don’t become a slave to the data.
CPAP therapy is there to improve the overall quality of your life and to help you with your health and general well being.
Getting stressed out over numbers that in isolation aren’t REALLY that useful, is counterproductive.
The best and worst part about modern CPAP machines is that they make data so readily available, your primary focus should be on how you feel and if you’re not feeling well, then look at the data and use that to inform your discussions with your sleep clinicians.
5 thoughts on “Understanding Your CPAP Data”
I would like to know what events per hour means when using a clap machine at night and what the numbers also means in front of it .
Excellent explanation of the CPAP data and tips for beginner CPAP users!
Great information Thank you
Hi I am just beginning a trial on an automatic Sleepwell cpap. My AHI was .4 the first nite and .6 the second. How do you interpret a number like this which isn’t even 1? Thank you!
Cpap user for 6 years. Just found your blog. A lot of good info!
Agree with everything you said. The problem is the sleepdocs (for whatever reason) are a slave to the data!
With cpap I had an ahi below 3 from day 1 (ahi during sleep study was 45). I was committed to using cpap, i was tired of falling asleep watching tv every night. First year of use, I was worse than without. Sleepdoc took one look at numbers, said 6+ hours a night, ahi 2.4. Keep up the good work.
But doc, I’m so tired.
Just hang in there it will get better.
Long story short, 7 months and 3 docs later, I found a doc that looked past the ahi and hours used. Had extreme flow limits and o2 drops at night. 6 months after that, 2 more sleep studies, a different machine (bipap), and I finally started to see improvement.
How you feel is the most important metric, but there needs to be education on the medical side too!!