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Reading stats and "throwing away" some apnea
04-06-2014, 08:47 AM
I watched a You Tube video from another site and the guy was saying that some apneas that show up are not really apnea at all, it depends on the time the apnea flags, is that right? How do you know how long an apnea lasts, and what is really happening when reading the Sleepyhead stats, is that the time in parentheses to the right of the time that the incident occurred? Also, how do you make your machine, in my case the ResMed S9 Elite begin the time that is ACUTAL rather than where it is, it begins at 18:30 which is 6:00 pm. I don't go to bed until 11:00, so when trying to see where these things occur, the time is off. Is there a way to set the internal clock?
04-06-2014, 11:00 AM
Hi marnid, I just went over my data from last nite on sleepyhead and found 2 hypopneas and 12 central apneas flagged this morning while i was wide awake and reading a book, cant explain why, but it happens, see setup manuals at the top of the forum for clock setup
04-06-2014, 11:36 AM
Easy questions first:
Quote:Also, how do you make your machine, in my case the ResMed S9 Elite begin the time that is ACUTAL rather than where it is, it begins at 18:30 which is 6:00 pm. I don't go to bed until 11:00, so when trying to see where these things occur, the time is off. Is there a way to set the internal clock?Since you are using a RESMED S9, the machine's clock can be set by going into the clinical set up menu.
Quote: How do you know how long an apnea lasts, and what is really happening when reading the Sleepyhead stats, is that the time in parentheses to the right of the time that the incident occurred?That number in the parenthesis is a good estimate how long the apnea lasted.
Now for the harder one:
Quote:I watched a You Tube video from another site and the guy was saying that some apneas that show up are not really apnea at all, it depends on the time the apnea flags, is that right?The short answer is: Yes, it really does depend on the time the apnea is flagged and what you were doing at that time, which is NOT recorded by the machine."
The long answer is: Unlike Santa Claus, our machines cannot know when we're sleeping and when we're awake. This is because our machines do not have any EEG data to work with. And for events to be real, they must occur when we are asleep when they start.
Now add in the fact that wake breathing is not as regular as sleep breathing. Even though we are not usually aware of it, wake breathing is, in fact, controlled by our voluntary nervous system. (Sleep breathing is controlled by the automatic (involuntary) nervous system that also controls our heart.) While awake, we do things like sigh every now and then; we do deep breathing for a while and then breath (much more) shallowly and/or much more slowly for a while; and we momentarily hold our breath while concentrating on something (sometimes something as simple as turning over in bed). All this natural variation in WAKE breathing can look like SLEEP DISORDERED breathing to our machines, and hence it is not uncommon for a PAP machine to score some false events during the times you are awake because the machine has no way to tell that you are awake when the events happen. What kind of events seems to depend on the person. For many people, these fake events will more likely be scored as CAs or Hs, but when I've run the experiment of consciously holding my breath at the beginning or end of the night, the fake apnea is just as likely to be scored as an OA as a CA; it may have something to do with how a particular individual holds their breath.
Now add in another phenomenon: The transition to sleep involves handing off control of breathing from the voluntary nervous system to the involuntary nervous system. And part of that "handing off the breathing" also involves a resetting of the CO2 levels needed to trigger an inhalation. The net result is that it is also not uncommon for there to be some short pauses in breathing while that CO2 trigger is being reset. These are almost always central in nature, and on an in-lab sleep test, CAs that are clearly sleep transition CAs are NOT scored as sleep disordered breathing unless they are so numerous that it is clear that they are preventing the person from smoothly transitioning from WAKE to SLEEP. Our machine scores these events because it has no EEG data to use to determine that a particular CA actually is a perfectly normal transition to sleep CA that would not be scored on an in-lab sleep test.
It's important to note that the machine's reported AHI is an approximation of the true AHI:
Machine reported AHI = (number of events detected)/(time machine was running)
True AHI = (number of events that occurred while asleep)/(time spent in Sleep)
For people who have very little WAKE time while using their machine, the
machine run time and the sleep time will be close enough to not make much of a difference. And the number of events scored while awake will (usually) be small (because the wake time is small), and hence they won't really affect the overall AHI all that much.
For people who have a lot of WAKE time while using their machine, there are two competing factors at work that influence the reported AHI versus the real AHI:
1) You've got the possibility of a fair number of "false" events---events scored when the user was actually awake. This increases the number of events (the numerator of the AHI), but (obviously) does not change the run time (the denominator). And so a large number of these false events might make the reported AHI higher than it should be.
2) You've definitely got the denominator of the AHI ratio wrong. Since the machine AHI uses "time machine was on and delivering therapy" as a stand in for the correct denominator "time the person was asleep", if there is a LARGE discrepancy between run time and actual sleep time, the reported AHI may be smaller (potentially much smaller) than the real AHI.
The common assumption in manufacturers seems to be that problems 1 and 2 will probably cancel each other out when it comes to a patient who is spending a lot of time in very restless dozing---going from WAKE to (light) SLEEP for long periods of time. And that's not an unreasonable assumption to make about aggregate data across large numbers of PAPers. But whether that happens for a particular individual really depends on the individual.
04-06-2014, 12:14 PM
(04-06-2014, 11:36 AM)robysue Wrote: Easy questions first:
Just a word of warning - there are problems with adjusting the S9 clock, as a number of folks have discovered by doing the Daylight Savings change. I would search the forum for "daylight", and find a thread titled "Twice a year clock change" and review the material there. One reply mentions:
Quote:If you set a new date or time that occurs in the past (eg. "fall back") then an 'invalid time/date, data exists for this period' message is displayed.
I believe the recommended technique is to adjust the clock in the afternoon or evening, allowing at least as much time before/after using the machine as needed, so that no data will be recorded with an "invalid" timestamp. Some have recommended doing the time change in small increments to avoid this problem. Others more experienced with this issue will correct me if I am wrong. I just don't want to erase ANYTHING, so I am cautious about the clock.
Good Luck. Now that I'v reminded myself about this issue, I have to go check my own clock. . .
04-06-2014, 12:46 PM
thanks so much. My DME guy is coming tomorrow, I am going to ask him to set the clock, LOL if he even knows how!!! thanks for the info on this again.
04-06-2014, 05:17 PM
(04-06-2014, 12:46 PM)Marnid2014 Wrote: thanks so much. My DME guy is coming tomorrow, I am going to ask him to set the clock, LOL if he even knows how!!! thanks for the info on this again.Setting the clock http://www.apneaboard.com/wiki/index.php..._the_clock
The machine have no way knowing whether you,re awake or asleep, events flagged while you,re awake are meaningless but otherwise pretty accurate. Both software shows the duration of an apnea event in seconds.
S9 data guide: http://www.resmed.com/au/assets/document...ow_eng.pdf
04-06-2014, 05:56 PM
Thanks Robysue for that info! I've only been doing this for a short while but figured there are some false calls in the data especially when I see a Central event corresponding to a huge leak moment. The Obstructive events seem scary real when corresponding to flow graphs but I'm still trying learn what I'm looking at.
04-06-2014, 06:03 PM
(04-06-2014, 05:56 PM)davek Wrote: Thanks Robysue for that info! I've only been doing this for a short while but figured there are some false calls in the data especially when I see a Central event corresponding to a huge leak moment.From http://www.resmed.com/au/assets/document...ow_eng.pdf
Unknown apnea: An unknown apnoea is an apnoea during which a leak higher than 30 L/min occurs, precluding accurate determination of whether the apnoea is obstructive or central.
04-06-2014, 06:26 PM
(04-06-2014, 06:03 PM)zonk Wrote:(04-06-2014, 05:56 PM)davek Wrote: Thanks Robysue for that info! I've only been doing this for a short while but figured there are some false calls in the data especially when I see a Central event corresponding to a huge leak moment.From http://www.resmed.com/au/assets/document...ow_eng.pdf
Thanks for that link.... If I read it about 60 more times, I might get most of it.
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