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Interpreting CA events
#1
Last night was my first time with my new CPAP machine. Everything went well except for some discomfort with the nasal pillows, which is probably a matter of getting them adjusted just right.

So I put the data card into SleepyHead and found a few of these CA events. During my original sleep study I had 10 Obstructive, 20 partial, 2 central, and 1 mixed apnea. Last night I had 7 CA events, which is a lot more than during the study. They all look pretty much like the attached picture.

The breaths become gradually shallower over 3-4 minutes, and then stop completely for around 10 seconds. I am suspicious of the fixed CPAP pressure. Only 6cm in my case, but it is constant. I remember several times lying there thinking that it was getting awfully tiring blowing out against the pressure. It was more annoying than the nasal pillow discomfort. And this is with EPR set to the maximum of 3. The SH pressure graph shows that the machine was properly lowering the pressure from 6 to 4 cm on each exhalation. (I think 4cm is as low as it will go). So perhaps in my sleep to "rest", I just give up and stop breathing.

Of course, during the sleep study and especially the titration study they do not let you alone long enough for this to be a problem.

My untreated apnea events normally seemed to happen while I am dreaming, and I do fine otherwise. But the fixed pressure from the machine is constant. I wonder if changing to APAP mode, range 4-6, would give me a bit of a rest when I did not actually have anything going wrong, even though 4cm is what the EPR drops to anyway. I am not going to mess with anything myself, but I am collecting information for the doctor.

I did try turning on the ramp feature (fixed, 15 minutes) to see if that would help me fall asleep. Nothing conclusive on that yet.


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#2
Others will provide more specific information about centrals, but I think it's important to remember that your sleep during the study is unlikely to be "typical", for many reasons. If, for example, you do tend to have centrals during REM, you may have had a lot less REM during the study, due to the unfamiliar surroundings. In addition, your first night with a new machine is also unlikely to be a typical night's sleep, so perhaps you had more centrals than normal for that reason. If you had a few alcoholic drinks during the evening, that could cause them as well, since alcohol is a central nervous system depressant. So you'll want to monitor for a week or so to see if the centrals are a trend.
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#3
Second night, being careful to avoid alcohol after 4pm. It still happens (see graph). Nothing seems to set it off - pattern is normal (00:20:45), then breathing gets deeper (00:21:30) before it trails off (00:22:15 to 00:22:50). This pattern repeats a few times, then does not happen again the rest of the night. It happend a total of 9 times. Only 2 obstructive events. Pressure was constant at 6cm thoughout.

btw, the clock at the bottom is early by an hour. The machine's internal clock seems to be set for Standard Time.


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#4
(04-27-2016, 07:22 AM)Sn00zeAlarm Wrote: Second night, being careful to avoid alcohol after 4pm. It still happens (see graph). Nothing seems to set it off - pattern is normal (00:20:45), then breathing gets deeper (00:21:30) before it trails off (00:22:15 to 00:22:50). This pattern repeats a few times, then does not happen again the rest of the night. It happend a total of 9 times. Only 2 obstructive events. Pressure was constant at 6cm thoughout.

btw, the clock at the bottom is early by an hour. The machine's internal clock seems to be set for Standard Time.

As I understand it, if over 50% of your AHI consists of centrals, you're considered to have complex apnea and are a candidate for ASV therapy, which is my own situation. I don't know if there's any absolute minimum number of centrals that they use as a criterion.

Before ASV, I was on APAP for four months (and before that, a straight CPAP without data for nine years). On APAP, my centrals varied wildly, from zero or just a couple on some nights to over a hundred. Now, on ASV, they're usually either zero or just one or two (I'm still tweaking settings), almost never any OAs; but my AHI (around 4 these days) is almost all hypos.

So, if the trend with the centrals stays the same for you, you may be switched to ASV, which has a complicated algorithm for dealing with them.
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#5
Although your machine is scoring CA, the wave form appears to contain some inspiratory flow limitation. I think lowering your pressure would be the wrong direction for you, however if you do so, just observe the results and how you feel, and decide if it's better or worse. Your pressures are already very low, and I think you will see more events at a lower pressure. Your events are of very short duration, and completely within acceptable levels. You didn't mention what your treated AHI is, but appears to be less than 2.0.
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#6
Average treated AHI was 1.52. Average during the sleep study was 5.2, so that is all good. But the peak AHI last night was 9, as ahown in the chart below. There is about an hour there where things were happening.

I need to get some AAA batteries for my oximeter and then I will be able to see if the SPO2 pattern looks the same as it did before treatment, and how the SPO2 drops line up with the CA and OA events.


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#7
So based on my own behavior, I ask what is your main purpose for chasing your central numbers? Are you just checking your treatment? Are you concerned that there is still a problem? Are you not feeling as good as you would like and are trying to identify the reason?

Your total number of apneas is not going to cause problems, the total count is low, the count per hour is low, and the duration is short. You can of course work to get the count even lower and you may or may not be able to do that.

If on the other hand you would like to feel better after sleeping with CPAP, then by all means watch your centrals, but I suggest that you do not limit your search to just your centrals. If you turn over in your sleep, many people will hold their breathe while they do that. This may be flagged as a central. You may be trying to clear congestion and getting flagged also.

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#8
I want to amend what I posted above. For diagnostic purposes, central apnea requires more than 50% centrals AND an AHI>5. Since your AHI appears to be well under 5, the handful of centrals wouldn't be a reason to change therapy. At least, that's how I've (finally) come to understand it.
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#9
PoolQ, I was just wondering why the number of CAs was higher than during the sleep study. But after last night, with motion-detection (a wrist FitBit) and an Oximeter, I can see that the few events I am getting are pretty random, and some can just be caused by turning over in bed. For example, as I am bracing one arm under me to roll over, and keep the blankets and hose from getting tangled, I tend to hold my breath for a few seconds.

Last night's AHI was just 1.35, and I do wake up feeling more alert in the morning. The pie chart shows 5 different kinds of events: hypopneas, CA, RERA, Obstructive, and unclassified, but only 2 or 3 of each kind all night. The oximeter records none of the wild swings and drops to 85% I was having before therapy - now median SpO2 was 95%. I'd say it is working!

The pattern of deeper, slower breaths just before a tapering off sometimes happens without going all the way down to a CA event, so it is a matter of degree of the same thing.
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#10
Your pressure is 6 cm H2O and you're using EPR = 3? That means that on exhale and at the very beginning of inhale, you only have 3 cm H2O. I honestly don't know how you tolerate such low pressure - I would feel like I'm suffocating. The machine you're using is designed to automatically set your pressure, so I don't know about using it as a CPAP - seems like a waste to me. Might as well set it to a conservative pressure range, and if it stays constant, fine, but if it detects an event is about to occur, it might be able to adjust to prevent it.

In any case, I recommend looking at a more long-term trend before adjusting anything.
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