Sleep study on mouth breather -- how do those nasal canulas tell you ANYTHING?!?

[cathyf]

Before late March of this year when I was finally convinced to wear a cervical collar, I don't believe that I ever slept with my mouth closed.

Not ever.

In my sleep studies, the only device that I'm aware of that was measuring flow rate were those nasal canulas (canulae?).

So how were they able to decide whether I was having apneas or hypopneas when they weren't measuring the majority of my volume of air that was moving in and out?

In my April sleep study, I supposedly had 106 hypopneas, and zero apneas of any kind. And I had 106 respiratory arousals, and 16 spontaneous arousals.

On a normal night with a full-face mask, I have probably 5 apneas for every hypopnea, but during the sleep study when my mouth was proabably wide open, zero apneas.

So is a sleep study just bogus when it comes to mouth breathers?

Another question...

Sometimes when I'm awake I'll feel my cheeks puffing out on an inhale, and then collapsing back down during the exhale. How can the machine tell how much  air is going in/out of my longs when I'm taking therapy air and holding it in my cheeks and then releasing it later?

[Gideon]

A properly setup study measures both mouth and nasal breathing. Either you are not remembering correctly or they set up wrong

the pap system measures the air delivered and the air returned, and it does account for intentional leaks.

[cathyf]

the pap system measures the air delivered and the air returned, and it does account for intentional leaks.

I'm not thinking about air that's leaking out, but instead some complex (and varying!) combination of air flowing from the nose and inflating the cheeks combined with air flowing down the windpipe and inflating the lungs. And then the lungs deflate on exhale and the cheeks deflate the oral cavity, and those are not necessarily synchronized. And the air being pushed out of the mouth can go back out the nose or into the lungs.

There are two other systems which work like this with blood flow rather than air flow -- but it's still fluid dynamics. The first is your aortic arch, which inflates during the part of your heartbeat which is expelling blood out of the heart into your bloodstream (systole) and then deflates during the part where the valve between the left side of your heart and your aorta is closed (diastole). This is what gives you blood pressure between heart beats. So, in round numbers, if your blood pressure is 120 over 80, that means that your blood pressure right at the heart is 200 when the valve is open and 0 when the valve is closed (it has to be zero when the valve is closed.) (This is also why the difference between systolic and diastolic pressure increases as you age, because your aortic arch gets less flexible over time. And why your systolic pressure needs to go up a bit, because otherwise your diastolic pressure would be so low that you would get dizzy, etc, during diastole.)

The second system is where your heart pushes blood from the right side of your heart into the lungs and then it goes from the lungs to the left side of your heart, and then pushed out into your aortic arch on the way to your body. This means that the blood on the right side is deoxygenated and the blood on the left is oxygenated. The thing that can go wrong is that before birth there is a hole between the two sides of the heart -- the baby isn't breathing, the lungs aren't inflated, so that system doesn't work. For some babies the hole is still open after birth, and so they get deoxygenated blood making it straight to the left side of the heart and then out into the body without going through the lungs first, and other blood sloshes through the other direction and goes through the lungs multiple times, and it's all mixed up and chaotic.

I'm questioning the ability of the machine to measure pressure coming back properly if there isn't a straightforward closed system of air coming up the nose and down the windpipe on inhale and back up the windpipe and down the nose on exhale. If you have some breaths where part of the inhaled air is collecting in the mouth, and other breaths where the exhaled air is coming from the mouth back down the nose. We talk about leak if the mouth is open, and that's one kind of problem, but I'm talking about what happens if the mouth stays closed and you have air just sloshing around in the backwater of the blown-up mouth cavity, which is randomly and chaotically collapsing closed and blowing back open. If there is any resistance in the windpipe at all, either direction, that the flow in and out of the mouth is going to be much freer.

[2SleepBetta]

Help me out here, aren't you writing of a "ventilatory regurgitation" similar to slight regurgitation  I had for a time before my TAVR-inserted bovine aortic valve's outer wall sealed off. The regurgitation reduced the blood flow pulse drive and volume, but nevertheless my LVEF could maintain life supporting  (though lessened) flow and O2+ needs. The regurgitation slightly diluted/"contaminated" the next pulse wave's flow volume.

I'd think (probably wrongly) what you describe is much the same with mixing of a FFM-wearing ("closed system" with a known bleed) sleeper's inbound 02+ and outbound CO2+: an EERS-like effect some use to treat CSR-like undulating FR envelopes, "waxing and waning" or periodic breathing.

Acknowledged: excessive mask leakage would upset all measures.

Edit: I assume a real sleep lab would have some means of measuring SDB cases where a nasal mask is involved, but have no idea how that would be done. I'd expect them to use a FFM once it was obvious you only mouth breathe. Otherwise, of course, they are wasting your time, efforts and money. Are you saying the whole test was done that way? Was your test conducted with only a canula?

[2SleepBetta]

Another couple of questions:

Are there two kinds of canula? One that senses pressure most directly and one that measures heat flowing out the nasal passages, the measure of which is converted to an air flow reading? Nevertheless, you'd expect either method used would yield results similar to the other one.

All this brings to mind the significant snippet from your FR curve that showed peak FR = 5, that is,  that 5 L/min peak airflow velocity.  I can more easily imagine a canula sensing the shape of a FR curve, using pressure or heat, but not as easily how it would sense delivery of volume, Tidal Volume. The sensing element's sufficient fill, heat or pressure sensing/loading area might accomplish that. But what about all the airflow in and out the mouth? Ahh. That's your point.

[NelsonM]

I wondered this when I did my at home sleep study to diagnose my OSA, my very first sleep study. Nasal cannula, no way to measure mouth airflow. I breathe almost entirely through my mouth. I asked the technician and he said it'd be OK. And it was OK. At least I got the diagnoses I think was right and the details of the sleep study chart matched my understanding of what's going on with me. I guess enough air passes through the nose to measure anyway? I believe I had a Type III study and it also measures chest movement, maybe that makes a difference. (It's possible I had a Type IV, not certain.)

On a normal night with a full-face mask, I have probably 5 apneas for every hypopnea

Is it possible you're comparing your OSCAR data at home with your CPAP and full-face mask to a sleep study you did without CPAP and just a nasal cannula? I don't think you can compare the two since the CPAP is actively changing things. But I probably misunderstand what you've done!

A properly setup study measures both mouth and nasal breathing.

I don't think the home test equipment I was given had any way to measure mouth breathing; just a nasal cannula. That seems common for the home sleep tests. Not as thorough as a full monitored type 1 or 2 setup in a clinic but it's what a lot of folks get now.