AHI stuck at 0.0?

[kongjie]

Hi. Haven't been in the forums for a while and when I looked at my first post, I realized I've been on CPAP therapy for over a year. Time sure flies.
I don't look at my data on the computer and in fact don't even regularly check the stats on the machine. Maybe once a week or so. But over the last few days I've been checking and every morning my AHI is 0.0. Like 3–4 days in a row now. If I understand correctly this is actually a moving average of 7 days? But is it unusual to have a consistent 0.0 reading? Could something be wrong with the machine?

[avi123]

I never had an AHI of 0.0. Neither the same daily AHI value, to the tenth decimal point, ever since I started the S9Autoset, 6 months ago. But, of course it's possible to have 0.0. If it happened to me I would take the flow generator section to my DME for free calibration.

[Otter]

But is it unusual to have a consistent 0.0 reading? Could something be wrong with the machine?

Try this:
_Hold down the start/stop button until the machine turns of.
_Unplug the machine.
_Wait at least 20 seconds.
_Plug it back in.

The S9's firmware is a bit buggy. Rebooting now and then helps a lot of odd data-related problems.

If that doesn't work, the next step would probably be to "erase all data" in the clinician's menu and reboot again.

[archangle]

Fake it out. Turn it on. Wait a few minutes.

Hold your breath for 30 seconds or so. Wait a minute. Repeat 5 or 6 times. See if it shows up in your results the next day.

Getting the software and looking at your data could help, too.

[avi123]

Check this:

http://s7.zetaboards.com/Apnea_Board/topic/8426123/1/

I doubt it if the following is correct:

The S9 units are able to determine if you're asleep or not based upon your airflow numbers as demonstrated by the wave form of your flow.

From the ResScan program, if you look at the flow charts, a sleeping waveform is "pointed" at the top and drops off rapidly. An awake waveform is more "rounded" at the top. The S9 machines "know" if you're asleep or not based upon which "pattern" your numbers fit. Here's a picture, comparing the two:


Sleeping Waveform:





Awake Waveform:



p.s. I am wondering where is builta:

[archangle]

First I've heard about that in the S9 machines. Does anyone have a reference for this from ResMed? It would be good to know about if it's true.

My "awake" waveforms don't look like that.

It's pretty simple to test. Someone with an S9 machine put it on and try it. Wear it for several minutes. Then hold your breath for 30 seconds or so and repeat half a dozen times over a span of a few minutes. Then look at your event counts with the software.

I tried that with my PRS1 machine, and it counted them, although it skipped the first two out of 4 events for some reason.

[ozze_dollar]

Some of you may remember I had a similar problem with my S9 VPAP. Turning the machine off for a while fixed the problem. I had complained to Resmed about the problem but they were of no help. They either dont know or dont want to know.

[Laos Film Director]

Hi. Haven't been in the forums for a while and when I looked at my first post, I realized I've been on CPAP therapy for over a year. Time sure flies.
I don't look at my data on the computer and in fact don't even regularly check the stats on the machine. Maybe once a week or so. But over the last few days I've been checking and every morning my AHI is 0.0. Like 3–4 days in a row now. If I understand correctly this is actually a moving average of 7 days? But is it unusual to have a consistent 0.0 reading? Could something be wrong with the machine?

kongjie, your machine is not registering properly. It's happened to me twice in the past year. The fix is easy. Just unplug for 5 minutes. Plug it back in and your good to go.

[Otter]

It's pretty simple to test. Someone with an S9 machine put it on and try it. Wear it for several minutes. Then hold your breath for 30 seconds or so and repeat half a dozen times over a span of a few minutes. Then look at your event counts with the software.

I've done this with mine, not to test the machine, but to get it to raise the pressure to clear my stuffy nose. It logs the events. I've learned to do a pretty convincing imitation of a string of obsructive apneas and hypopneas. To convince the machine I'm having an OA, it helps to exhale, then block my airway with my tongue while holding my breath. Holding my breath my lungs full doesn't seem to be as convincing, but I'm not sure if the machine scores these as centrals or has a BS detection algorithm.

I tried that with my PRS1 machine, and it counted them, although it skipped the first two out of 4 events for some reason.

Did you compare the waveforms of your simulated events with real ones. I've noticed that in some of my failed FAs, there is a little activity in the flow trace where it should be flat except for FOT. Jamming your tongue back in your throat helps stop this autonomic cheating. I've seen similar spots in my real data, and the machine doesn't score those as OAs either. IIRC, it counted one as part of a hypopnea.

[avi123]

Fake it out. Turn it on. Wait a few minutes.

Hold your breath for 30 seconds or so. Wait a minute. Repeat 5 or 6 times. See if it shows up in your results the next day.

Getting the software and looking at your data could help, too.

Reply:

While testing the S9Autoset, Resmed did just that. First they did Bench Testing, next subjects were faking apneas, and lastly the machine was tested on sleeping patients:


http://www.resmed.com/us/assets/documen ... -paper.pdf

[LittleRedTruck]

I occasionally reach 0.0. Last nite I slept 8.3 hours and my AHI was about .7. So I maybe had one event last nite. didn't read card so guessing on that. But do know it will report 0.0 if no events. Dan

[robysue]

If I understand correctly this is actually a moving average of 7 days?

On the S9, the number on the short sleep quality report is the overnight AHI if I recall correctly. (Been a while since I've used an S9.) In the longer version of the sleep quality report you can select from one day, seven day, and thirty day averages.

Others have addressed the issue of how to reboot your machine and why you suspicion that the AHI = 0.0 for several days in a row may be warranted.

I second running archangle's experiement: Mask up and breath normally for a few minutes and then hold your breath as long as you can. And repeat several times. Try to make sure some of the "breath holding" starts after an exhale rather than an inhale. Harder to do, but that's important.

And make sure the RAMP is NOT on when you do your experiment: If I recall correctly, the S9s do NOT flag events that occur during the ramp up time.

[Bobby269]

I use the Resmed Autoset. On good sleep nights I can have an 0.0. It happens once or twice a week. On less sleepy night it gets up to 0.3, 0.5.

[archangle]

Reply:

While testing the S9Autoset, Resmed did just that. First they did Bench Testing, next subjects were faking apneas, and lastly the machine was tested on sleeping patients:


http://www.resmed.com/us/assets/documen ... -paper.pdf

What relevant info did you glean from the paper, avi? Does the S9 ignore events while the patient is awake, or does it record them? In a quick scan, I didn't see any indication that the S9 tries to tell the difference.

[Mark184]

I have many nights where I have an AHI of 0.0. Most other nights it registers a 0.2. I mentioned this to my DME and he told me he was not surprised since the doctor had diagnosed me with respiratory arousals not induced by apneas. He (the DME) said that AHI cannot measure those. Is he giving me a line? (I've only been at this for 3+ weeks now so I'm still new and gullible). I did google respiratory arousals and AHI and did find articles that said the two are unrelated, and therefore AHI's do not reflect respiratory arousals. I meet with my actual sleep doctor next week and will consult with him.

For what it's worth, I have unplugged the unit many times and reset. No difference.