2,745
edits
Changes
m
clarity
= Basic data interpretation: Daily Detailed Data =
The amount of data available in SleepyHead can be overwhelming to new PAPersCPAP users, particularly those who only want some reassurance that "things are working." While many newbies tend to focus on the data in the Statistics tab and the Overview tab, the data in the Daily tab is usually more useful when you are trying to analyze what's going well and what's not going so well during the CPAP adjustment period. Moreover, the Daily Detailed Data is currently more robust and less buggy than the data presented in the Statistics tab. So I would encourage new SleepyHead users to first concentrate on getting comfortable with their detailed Daily data. Even so, you want to look at the detailed Daily data in context: One bad night does not mean things are suddenly not working; a month of bad nights does indicate something is wrong.
Most of the focus in this article is on how the daily data looks for ResMed and PR machines. But most of it still applies to the data SleepyHead shows for any of the machines that it supports.
You'll note that the machine had been decreasing the IPAP pressure (since the breathing was stable) for several minutes before the OA occurred. Neither the patient's EPAP (which is at its minimum value) nor their IPAP is increased for this particular OA because it's isolated. There's not another OA or H within 2 minutes of this particular OA.
The fact that APAPs and auto bi-levels do not respond to isolated OAs and Hs seems counter-intuitive to many new PAPersCPAP users. But this lack of response is intentional and it mimics the [http://www.apneaboard.com/040210.pdf AASM Clinical Guidelines for Manual Titration Sleep Studies]. The idea is not to jack up the pressure every time any event happens: That can lead to more unstable breathing, discomfort, and more pressure than is needed to keep the airway open most of the time.<br />
'''Question''': Why is my pressure increasing when there don't seem to be any events?
On the other hand, the minimum pressure needs to be high enough where the machine does not need to increase the pressure by a significant amount during the first cluster of events. Sharp rapid increases of 5-8 cm of pressure in 10 minutes might not allow the airway enough time to stabilize and settle down. And unstable breathing can cause further events, which leads to more pressure increases and more unstable breathing.
And then to muddy the waters even further: Approximately 10-15% of PAPers CPAP users may have a tendency to develop pressure-induced central apneas if the pressure setting is too high. And what "too high" ''is'' strongly depends on the individual. And while modern machines have algorithms to distinguish central apneas from obstructive ones, those algorithms are not perfect, and there is some evidence that the algorithms may be more likely to mis-score CAs as OAs when the CAs occur at relatively higher pressures.
So blindly increasing your pressure just because the machine is running at or near your maximum setting all night long is not a good idea. Before you decide to change your pressure settings, you really need to do some careful thinking about what you hope to accomplish by changing the pressure and have a plan on how to evaluate whether the change does what you intend it to do. And keep in mind that it really is a good idea to consult your sleep doctor about any changes to your therapeutic settings.<br />
'''The AHI Graph'''
This graph is often misunderstood by many new PAPers CPAP users and because of that, we often recommend new SleepyHead users simply ignore this graph.
And yet, many newbies are very interested in this graph. So in the interest of trying to clear up misconceptions about this graph, it is included here.
* ''Show Leak Redline.'' The default is to have this checked and the default value for the Redline is the ResMed value of 24 L/min. This is a NEW feature in SleepyHead 0.9.6. If you are using a ResMed S9, it's strongly recommended that you make sure Show Leak Redline is checked. If you are using a different machine, this may be a useful option for you, but you will need to change the value for the Redline. More on that later.
* ''Show compliance'' affects how low usage days show up in the Overview data and the compliance data in the Statistics page. The default line is 4 hours for obvious reasons. It's suggested that you leave this alone.
* ''Custom User Event Flagging.'' It's recommended that a new PAPer CPAP users leave this unchecked. It can be useful if you have a lot of "almost" apneas or "almost" hypopneas showing up in your detailed data, but it really is an advanced feature.
* ''AHI/Hour Graph Settings.'' The default is to have the box by Zero Reset unchecked. Leaving the box unchecked tells the AHI/hour graph to keep a running total of the number of events (OAs + CAs + Hs) that have happened in the last 60 minutes. To make the AHI/hour graph behave like the ResScan AHI/Hour graph, you need to check the Zero Reset box; then the AHI count is set back to 0 at the top of every hour.
<br /><br />
All masks leak-- they all have an intentional leak rate built into their design to prevent re-breathing of CO2. This intentional, expected leak rate varies with the pressure level: As the pressure goes up, so does the intentional leak rate for the mask. The leak rate also varies from mask to mask. Typically full face masks have larger intentional leak rates than nasal masks or nasal pillows masks when used at the same pressure.
Excessive leaking is when the total leak rate detected by the machine is larger than the intentional leak rate for the mask. Excessive leaks are an ongoing issue for some PAPersCPAP users. A full understanding of the leak information reported by SleepyHead requires that you understand what kind of leaks your machine reports and how your machine's manufacturer ''defines'' Large Leak.
'''''NOTE and CAUTION:''''' When looking at Leak/Total Leak lines in both your data and others, you must take into consideration all of the following:
<br />
A lot of long-time PAPers CPAP users will say that the "30% time in Large Leak territory" is too generous and that Large Leaks will affect your therapy much sooner than that. So this may be a good rule of thumb for you to consider:<br />
''
As with many other things concerning PAP therapy, trending data in the Leak/Total Leak line is also important. If you're trying out a new mask and you're still working out how to fit the mask, you may have one or more nights of really bad Large Leaks. If your mask cushion is starting to wear out, the first sign might be a higher than normal leak line. If you wind up with a bad cold or the flu and you're seriously congested, you might be prone to doing more mouth breathing than normal and your leaks may be (much) higher than typical. So it's important to not over-react to one (or a few) bad nights with respect to leaks, particularly if there's an obvious explanation.
But some new PAPers CPAP users (and not so new PAPersCPAP users) have real problems getting excessive leaking under control. We now turn our attention to using the Leak/Total Leak line to identify when Large Leaks are '''long enough''' as well as large enough to compromise the efficacy of the PAP therapy and the accuracy of the data.
There is some differences of opinion among long term PAPers CPAP users about how much time you have to spend in Large Leak territory before it becomes clear that you absolutely must do something about the leaks. Some people would say 10% of the night in Large Leak territory is too much; others would say 10% is ok, but 20% is not. Some of this comfort: If the Large Leaks are waking you up, they've got to be dealt with. If you're not feeling better in the daytime, the Large Leaks might be part (or all) of the problem. But if you're sleeping through the Large Leaks and you're feeling good in the daytime, it may not be all that important if you are in Large Leak territory 10-20% of the time on some nights.
But by the time Large Leaks make up 30% or more of the night, you have a problem. ResMed is explicit about this line; the other manufacturers are more vague.
A lot of things can cause leaks of all sizes: Fiddling with the mask, jostling the mask to scratch your nose, jostling the mask while turning over in bed, mouth breathing, and facial relaxation (facial sagging) in deep sleep are all capable of causing both small and large leaks. Worn out mask cushions, incorrectly sized masks, overtightened mask straps, and masks that are incorrectly reassembled can also cause leaks. Another potential cause of leaks are pressure increases when using a PAP in auto mode. Fitting a mask at low pressure tends to be easier than fitting a mask at higher pressures. And if you fit your mask at relatively low pressure, as the pressure increases, the pressure increase itself may cause the mask to lose its seal, and the result is an excessive leak.
Mouth leaks can be particularly problematic for nasal mask and nasal pillows users. Indeed new PAPers CPAP users using nasal masks and nasal pillows are often told by other PAPers CPAP users that they need to use a full face mask if there is any chance that they might be a mouth breather. And when a newbie posts pictures of problematic leak lines, the first thing that's often suggested is that the leaks are probably due to mouth breathing.
But a leak is a leak no matter where it is coming from, and the machine doesn't know where it is coming from. So how do we determine if a leak is a mouth breathing leak or just a typical mask leak caused by something else? Well, it's kind of difficult, but in general we look at the leak line on the graph. Short brief spiky leaks are very likely mask movement leaks... brief refitting or minor movement. Longer periods of spiky leaks may indicate that you were very restless and doing a lot of tossing and turning and repeatedly jostling the mask in the process. Mouth-breathing leaks tend to have a longer period of leak and often tend to sort of create a a mesa or plateau effect. But facial relaxation can also lead to longer periods of leak that look like mesas or plateaus.
Most sleep doctors and most OSA patients never really concern themselves with detailed efficacy data beyond the nightly and long term AHI data. And that's ok: If the nightly AHIs are almost always below 5.0 and you're feeling well, there's really no need to look at the detailed data available in SleepyHead about each and every event the machine recorded over night. But if you're a data hound, the stuff you can see in the Flow Rate data can be fascinating. And if you're not feeling as well as you hoped with CPAP therapy, sometimes examining the Flow Rate data in more detail can shed some insight into what might be going on.
The information on this page is written for the curious PAPer CPAP users who simply wants to know more about what the Flow Rate data shows and what it may indicate about the quality of therapy. None of this information should be considered medical advice. If you are experiencing problems with your PAP therapy, you should consult your sleep doctor.
On an in-lab sleep test (PSG), each apnea will be classified as either an ''obstructive apnea'' or ''central apnea''. The data from the belts around the chest and abdomen are used to distinguish between the two types of apnea on a PSG. If the belts indicate that the patient is trying to breathe, but no air is getting into the lungs, then it's assumed that the problem is that the upper airway has collapsed and the apnea is scored as an ''obstructive apnea''. But if the belts indicate that the patient is making ''no effort'' to breathe, then it's assumed that the problem is that the brain has "forgotten" to send the signal to the diaphragm and lungs to inhale. The patency of the airway is irrelevant when scoring a central apnea on a PSG because the main problem is with the brain's forgetting to tell the diaphragm and lungs to breath. And it's possible for the airway to collapse during a central apnea.
But our CPAPs have no way to determine the effort to breathe. Hence CPAPs cannot distinguish between obstructive and central apneas in the same way that the technician monitoring a PSG does. Originally full efficacy data CPAPs did not try to distinguish between obstructive and central apneas. (The F&P Icon still does not try to distinguish types of apneas.) But when manufacturers started designing Auto CPAPs, a potential problem had to be addressed in the Auto algorithms: A minority of PAPers CPAP users are sensitive enough to pressure to develop problems with pressure-induced central apneas. And the tendency to have problems with pressure-induced centrals is more pronounced the higher the pressure setting on the CPAP. Hence early APAP Auto algorithms often were designed to NOT increase the pressure in response to apneas scored at pressures of 10cm or greater. In an effort to get around this difficulty, many of the current generation of full efficacy CPAPs make an effort to distinguish between apneas are presumed to be obstructive and those that are presumed to have a high probability of being central, and an APAP with such a "central apnea detection" algorithm can be programmed to respond to the apneas classified as obstructive and ignore the other apneas.
ResMed and PR PAP machines use (different) proprietary algorithms to test the patency of the airway and use the result to classify each apnea as a ''clear airway apnea (CA)'' or an ''obstructive apnea (OA)''. When the data from the algorithm leads to an ambiguous result, the apnea may be scored as an unknown apnea (A or UA). Both ResMed and PR Auto machines will increase the pressure in response to clusters of OAs, but they will not increase the pressure in response to apneas scored as CAs.
<br />
This particular hypopnea's flag is more or less in the middle of the hypopnea. Most of the time the flag is closer to the end of the event, but there is some variability. Another thing that's worth pointing out is that the patient's BiPAP is in the middle of decreasing the IPAP as part of the PR "search" algorithm; the isolated H does not cause the machine to increase the IPAP and that's a bit counter intuitive to some PAPersCPAP users. But it is how the PR Auto algorithm works: It ignores isolated Hs and OAs; pressure is increased for events only if two or more events occur very close to each other.
'''Clusters of events'''
One common concern PAPers CPAP users have about their data are clusters of events. It's important to understand that your CPAP machine is not going to prevent every apnea. If you have a bad night now and then with some clusters of events, it's not something to worry too much about. But if you tend to see dense clusters of events on most nights, your CPAP therapy may not be optimized.
Figuring out what's causing clusters of events can be difficult: Sometimes clusters of events occur in REM sleep. Sometimes clusters appear during back sleeping. Sometimes clusters of events are just sleep/wake/junk breathing. Occasionally clusters of events may be an indication that you're in the unlucky 10-15% of PAPers CPAP users who have problems with pressure-induced central apneas.
There's no clear way to tell what caused any particular cluster of events. Our CPAPs do not have EEGs and there's no way to definitively tell when REM sleep is occurring in the data. Likewise our CPAPs have no position detector, so the data can't directly tell us whether supine sleep is the problem. If you remember being awake or restless at certain period in the night, then it may be possible to identify a cluster as probably being sleep/wake/junk, but it's not uncommon to have no real memories of a restless period during the middle of the night. Long clusters of central apneas at times you think you were asleep obviously raise the question about pressure induced centrals.
'''How APAP machines respond to events'''
New PAPers CPAP users are sometimes surprised by the fact that their CPAP did nothing when an apnea was in progress. There's an assumption that the positive air pressure provided by the CPAP is supposed to "blast" through the obstruction and restart the breathing. But pressure is not used to try to "end" an on-going event. It's not even clear that 20cmH20, the maximum pressure delivered by a CPAP, would even be effective at trying to "blow" a collapsed airway open: 20cmH20 is not enough pressure to effectively blow up an ordinary balloon. In fact, 20 cmH20 is about the difference in atmospheric pressure between a very stormy, low pressure day, and a bright sunny high pressure day.
The basic idea in CPAP therapy is to provide (a small bit of) positive air pressure through the entire breath cycle to make it more difficult for your airway to collapse. This system is very good at preventing apneas and hypopneas from occurring, but it is not perfect: A few events will likely occur each night, but the overall number of events will be low enough to keep your treated AHI under 5.0, and probably well under 5.0, each night you use the machine. In other words, a well-adjusted CPAP makes it difficult, but not impossible for your airway to collapse.
Donate to Apnea Board
