NCHawk wrote:For the last month or so I've noticed something strange with my CPAP readings. Every so often when I check the info reading in the morning it will show a "bad mask fit" but also a low AHI. I use Sleepyhead, but don't check the readings every day and when I do I can't always remember which days this happened so I haven't been able to verify if there's any correlation between the bad mask fit and things like leakages.
By "bad mask fit", do you mean Mr. Red Frowny Face is paying you a visit in the short version of the Sleep Quality Report when you check the S9's LCD in the morning?
If so, then you need to understand the meaning
of Mr. Red Frowny Face's appearance. He shows up on the short Sleep Quality report when your 70% leak rate
is AT or ABOVE 24 L/min. In other words, Mr. Red Frowny Face only shows up when your unintentional leak rate is AT or ABOVE 24 L/min for at least 30% of the night. This is when the Resmed engineers believe both the SIZE and overall LENGTH of the unintentional leaks are LARGE enough to adversely affect both your therapy and your data.
To give you an idea of just how bad the leaks have to be to get Mr. Red Frowny to show up in the morning, consider this: 30% of one hour is 18 minutes. If you sleep 7 hours, that means that you have to have 126 minutes (just over 2 hours) of leaks above 24 L/min for Mr. Red Frowny Face to show up.
So, yes, there is a most definite correlation between Mr. Red Frowny Face and leakages. Look at your SH data. Find days where your leak line is frequently above 24 L/min or is above 24 L/min for extended periods of time or both. Those are the days where Mr. Red Frowny Face was likely to show up.
And why this has just started to happen intermittently in the last month or so?
Possible culprits: Is the mask cushion beginning to deteriorate? Are you doing some significant mouth breathing on some nights? Spring allergies kick in yet? That could induce the mouth breathing. Are you sleeping in a very different position some nights? Was the hose (and mask) properly assembled on those nights? Any chance the humidifier cover was not completely clicked shut?
Would a bad mask fit affect the AHI reading? Is there anything I should be looking for in the Sleepyhead graphs (some of which I'm not sure I understand anyway) to figure out what's going on?
Yes Mr. Red Frowny Face affects the AHI reading: Resmed engineers have set the threshold for Mr. Red Frowny Face's visits at the level where they believe leaks are a SERIOUS issue that indicate that both your therapy and your data could be compromised. That means:
1) The leaks are high enough that the machine may not be able to detect events correctly. Hence the reported AHI number may be lower than it actually is.
2) The leaks are high enough that the machine may not be able to effectively maintain enough pressure in your airway to keep it from collapsing. Hence you may be having more (possibly many more) events that you usually have with therapy.
Looking at the data in SH will let you determine whether the problem on a given night is one or more very long
leaks or whether the problem is caused by very, very numerous
but short-lived large leaks
. But beyond that I'm not sure what else the leak line will tell you about the problem.
My advice? Treat a visit from Mr. Red Frowny Face seriously. When you see him, make a written note so you DON'T loose track of the dates he shows up. Make any additional notes about your impression of the night while it is fresh in your mind: Did you wake up? A lot or a little? Any evidence you took your mask off in your sleep? Did you wake up with a dry mouth--either in the morning or during some time in the night? Did the spouse say you were snoring? Does the spouse remember any weird noises coming from your mouth or your mask? Did you reassemble the equipment that day? Did you swap the hose or mask cushion out for a different one? Use the leak line data in SH to figure out WHEN you had the large leak and how long it lasted. And try to correlate what you see in SH with your written impressions about what went bump in the night: One really long large leak with a vague memory of either taking the mask off or waking up without the mask indicates one problem; dozens of minute or two long large leaks with a vague memory of fighting "face farts" most of the night indicates another problem; and waking up with a dry mouth or the wife reporting weird noises points to a third kind of problem.