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How SLeep Study Gathers Information
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me50 Offline

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Post: #1
How SLeep Study Gathers Information
I have had 2 sleep studies, one without CPAP but was put on CPAP the same night and one that started out with CPAP.

okay I'm on my phone right now and was trying to explain my questions better and I hit post reply to send as soon as I get to a laptop I will redo my question
(This post was last modified: 10-31-2013 09:41 PM by me50.)
10-31-2013 08:12 PM
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sir_sleeps_alot Offline

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Post: #2
RE: How SLeep Study Gathers Information
I ask LOTS of question and this is what was explained to me:

Two straps around the abdomen measure breathing effort and the prong and/or prongs and temperature sensor detect airflow. A probe on the finger measures your oxygen level.

Apnea = No airflow for 10 seconds or more
Hypopnea = 30% reduction in airflow lasting 10 or more seconds involving a decrease in oxygen saturation of 4% or more

Obstructive = Attempt to breathe (muscle activtiy/chest expansion)
Central = No attempt to breathe (no muscle activity/no chest expansion)

If the chest/belly straps show effort but there is a reduction or cessation of airflow, it's obstructive apnea/hypopnea. If there's minimal/no effort, it's a central apnea. I don't know if this is a common opinion, but my doctor feels that if it improves with cpap, it must be obstructive.

A person's AHI (Apnea/Hypopnea Index) is simply the average number of apneas and hypopneas (of any type) you have per hour. They tally up the number of apneas you had with the number of hypopneas you had and divide it by the number of hours you slept during the study.

There are other probes that measure brain waves (to determine what stage of sleep you are in), heart rate, leg movements, eye movements, and probably some things I've forgotten. These things help diagnose/rule out other medical problems and to provide info about the severity of your apnea.

Hope that's helpful.
(This post was last modified: 10-31-2013 09:21 PM by sir_sleeps_alot.)
10-31-2013 09:15 PM
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robysue Online
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Post: #3
RE: How SLeep Study Gathers Information
(10-31-2013 09:15 PM)sir_sleeps_alot Wrote:  Hypopnea = 30% reduction in airflow lasting 10 or more seconds involving a decrease in oxygen saturation of 4% or more
This is the so-called AASM Recommended standard that Medicare recognizes. There is another standard called the AASM Alternative standard for scoring Hypopneas that requires a 50% reduction in airflow and ONE of the following: Either an EEG arousal OR a decrease in oxygen saturation of 3% or more.

It is commonly assumed that for most people the choice of the standard for scoring hypopneas will make little statistical difference in diagnosis, but there are subpopulations where the differences in the standards of scoring the hypopneas can lead to extremely different diagnoses. I'm one of those people: On my initial diagnostic study, the hypopneas were scored under the Alternative standard and all of my hypopneas were scored because of EEG arousals rather than O2 desaturations. I also had a about 14 OAs scored during 4.77 hours of sleep If my study had been scored under the Recommended standard, my AHI would have been 3.5 and I would have had no diagnosis. But with 78 "hypopneas with arousal" scored under the Alternative standard in 4.77 hours of sleep in addition to the 14 OAs, my official AHI/RDI for the study was listed as 23.1, and I walked away with a diagnosis of moderate OSA.

See http://www.ncbi.nlm.nih.gov/pubmed/19238801 and http://www.journalsleep.org/ViewAbstract.aspx?pid=27368 for scholarly discussions of how and when these two standards affect a patient's diagnosis of OSA as well as the formal definitions of the two standards.
(This post was last modified: 11-01-2013 12:26 PM by robysue.)
11-01-2013 12:24 PM
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me50 Offline

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Post: #4
RE: How SLeep Study Gathers Information
robysue

I understand what you are saying about the 2 different methods, however, I wonder if the electrodes and the CPAP machine (during titration) shows apnea and what type of apnea (without chest and abdomen belts).
11-01-2013 07:20 PM
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robysue Online
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Post: #5
RE: How SLeep Study Gathers Information
(11-01-2013 07:20 PM)me50 Wrote:  r I wonder if the electrodes and the CPAP machine (during titration) shows apnea and what type of apnea (without chest and abdomen belts).
Not quite sure I follow what your question is. On the titration study, the tech has both the EEG data and the data from the belts to determine whether a "non-breathing spell" occurs during sleep (and hence is a real "sleep apnea") and whether the apnea is an obstructive apnea or a central apnea. So I think you must be asking about the data recorded by our machines when we're sleeping in our beds each night. So I'll restate what I think you're asking:


1) How does a full efficacy CPAP machine decide when to record an event since it doesn't have any EEG data?

The machines we use each night approximate the true data when they record apneas and hypopneas. Our CPAP machines do not know when we are awake because they do not have EEG data. Our machines do not know when we are making an effort to breath because they do not have data coming from the chest and abdomen belts. All our CPAPs have is the data about the airflow into and out of our lungs.

Typically a full efficacy data machine's algorithm will record an apnea of some sort when the airflow suddenly decreases by 80% of the running baseline for at least 10 seconds. (The running baselin is computed from the last several minutes of breathing.) If I recall correctly, both the Resmed S9 and the System One will score a hypopnea when the airflow decreases by something like 40% of running baseline for at least 10 seconds.

Full efficacy data machines do not have any way to determine the sleep state. Hence they will score an apnea or a hypopnea whenever the airflow drops sufficiently for at least 10 seconds. In other words, the machine makes the assumption that if you're using the machine, there's a very high probability that you are asleep. For folks without any insomnia problems, that's a very reasonable assumption.

But if you have the mask on for extended periods of time while you are awake, you may see many "false" events scored during the wake time. The reason why is this: Wake breathing is much more irregular than normal sleep breathing and there are normal wake breathing patterns that will fool the machine. For example, it is not uncommon for people to hold their breath for several seconds while concentrating on something. Hold your breath for 10 seconds or so, and an apnea is likely to be scored. We also tend to vary the depth of our inhalations and exhalations on a regular basis when we are awake. We may consciously do several minutes of deep, relaxing "yoga" breathing for a while followed by several much shallower breaths. And those shallower breaths can meet the criteria of a hypopnea since the machine is not aware you're awake and doing "yoga" breathing ...


2) How does a full efficacy data classify an apnea as either a CA or an OA since it has no data from the chest and abdomen belts?

The full efficacy machines that can classify apneas into CAs and OAs use proprietary algorithms.

The Resmed S9 machines use a proprietary FOT algorithm that uses a rapid series of oscillations in pressure to determine the patency of the airway. The FOT algorithm uses the what happens to the back pressure during the FOT oscillations to determine whether the airway appears to be clear (open) or obstructed (blocked). If the airway appears to be clear, the machine scores a CA and if the airway appears to be obstructed, the machine scores an OA.

The PR System One machines use a proprietary PP algorithm that uses one or more "pressure pulses" to determine the patency of the airway. (A "pressure pulse" is a sudden, brief 2cm increase of pressure that is immediately reduced back to the pressure setting.) If the airway appears to be clear, the machine scores a CA and if the airway appears to be obstructed, the machine scores an OA.

Both the S9 FOT algorithms and the System One PP algorithms are ways of providing intelligent guesses about the real nature of the apnea that is scored by the machine. The presumption in both machines is that if the airway is clear (unblocked) the problem must be central in nature and hence, the apnea is likely an CA. And the presumption is that if the airway is obstructed (blocked), there is a high probability that the patient is trying to breath, but the blocked airway is preventing air from flowing into and out of the lungs. Are the FOT and PP algorithms perfect in detecting the patency of the airway? No, but they are pretty decent. In both cases, if the machine scores a CA, the airway is probably clear and there is a high probability that the apnea is central. But both machine may mis score a real central apnea as an OA because the air way can be collapsed during a real central apnea on an in lab PSG.

Hope that answers some of your questions.
11-01-2013 11:58 PM
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me50 Offline

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Post: #6
RE: How SLeep Study Gathers Information
Robysue thanks for the info no I am actually talking about during the sleep study because I did not have belts on me during my sleep study
(This post was last modified: 11-02-2013 01:47 AM by me50.)
11-02-2013 01:37 AM
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robysue Online
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Post: #7
RE: How SLeep Study Gathers Information
Was your titration study done in a lab or was it just done at home with the aid of an an APAP? If it was done in the lab, what did they monitor? Did they use an EEG? Did they put an O2 montor on you?

If the titration study was done at home with just an APAP (no EEG wires, no belts, and no O2 monitor), then the detection of events was just through the machine's algorithm which uses nothing but back pressure in the hose to detect the air flow into and out of your lungs (which is highly accurate) and the machine's FOT or PP algorithm for deciding on whether any given apnea was a CA or OA.

The presumption in reading the data would be that as long as you were asleep most of the time you were using the machine, the data was accurate enough to get a decent picture of how your OSA was responding to the pressures generated by the APAP. (It turns out that a week or so of autotitration on an APAP without any other data usually gives as decent idea of the correct pressure level needed to control the OSA as a one night in a lab does. For some people, it gives a better idea.)

If you had an O2 monitor attached to your finger, but no EEG wires during a home titration study, then the O2 data would be looked at to help confirm which hypopneas scored by the machine were accompanied by O2 desats that were great enough to be scored under the AASM Recommended Standard, which might have some implications if you are on Medicare in the US. The O2 data would also help tease out how good a job the APAP was doing in preventing O2 desats if you had significant O2 desats on your diagnositic sleep study.

If you had EEG wires attached to your head during a home titration study, then the EEG data would be used to determine your sleep state during each event the machine recorded and the events recorded during WAKE would be discounted, or thrown out.


If you had an in lab study that had EEG wires attached to your head, then the tech would be able to tell when you were awake and when you were asleep. And the person scoring the test would discount any events scored during the period when the EEG data showed that you were awake. But without any data from the belts, the classification of the events would have to be based on the proprietary FOT or PP algorithm of the titration unit used in the study.
11-02-2013 02:34 AM
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me50 Offline

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Post: #8
RE: How SLeep Study Gathers Information
(11-02-2013 02:34 AM)robysue Wrote:  Was your titration study done in a lab or was it just done at home with the aid of an an APAP? If it was done in the lab, what did they monitor? Did they use an EEG? Did they put an O2 montor on you?

In a lab and I had all the wires attached to me and I had the O2 sensor on my finger.


The presumption in reading the data would be that as long as you were asleep most of the time you were using the machine, the data was accurate enough to get a decent picture of how your OSA was responding to the pressures generated by the APAP.

I had the machine on about 6 hours with recorded sleep of 2.9 hours during the sleep study in the lab.
Thanks for the info.

If you had an in lab study that had EEG wires attached to your head, then the tech would be able to tell when you were awake and when you were asleep. And the person scoring the test would discount any events scored during the period when the EEG data showed that you were awake. But without any data from the belts, the classification of the events would have to be based on the proprietary FOT or PP algorithm of the titration unit used in the study.
(This post was last modified: 11-02-2013 02:50 AM by me50.)
11-02-2013 02:49 AM
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Post: #9
RE: How SLeep Study Gathers Information
In anyone's experience, or maybe opinion, is the lab study more accurate or the home study? I have read several "papers" on this and am still confused. Help if you would.
11-06-2013 12:35 AM
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robysue Online
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Post: #10
RE: How SLeep Study Gathers Information
(11-06-2013 12:35 AM)Blaifarm Wrote:  In anyone's experience, or maybe opinion, is the lab study more accurate or the home study? I have read several "papers" on this and am still confused. Help if you would.

It depends on what you mean by accurate.

In the sleep lab, the accuracy in determining whether an apnea or hypopnea has occurred while you are asleep is far, far greater than on the standard home sleep study. Likewise, the ability to sort out which apneas are central and which ones are obstructive is more accurate in the lab. Measuring the O2 levels is likely to be more accurate in the lab because there's someone there monitoring things----if you manage to rip one or more of the wires off during the night, the tech can come in and put the stuff back on you . (The O2 monitor is probably the most common thing that comes off.) Home sleep studies usually make little or no effort to measure PLMs and hence they won't be of use for diagnosing PLMD, which is another common sleep disorder that can have many of the same symptoms as OSA. (And it is also possible to have both PLMD and OSA at the same time.)

But: You are sleeping in a new and strange environment when you do an in lab sleep test. The bed may be harder or softer than your own. The room may be warmer or colder than your own. Bedtime may be much earlier than your normal bedtime. Wake up time may be much, much earlier than your normal wake up time. All these things factor in as well and they can all can seriously skew the results of an in-lab sleep test simply because you may not sleep very well during the test. It may take you much longer to get to sleep than normal. You may wake up more frequently than normal. You may not get as much REM or Stage III sleep as normal. In short, your sleep efficiency may be seriously compromised by sleeping in the lab. And that could lead to either overestimating or underestimating your AHI---depending on when your OSA is at its worst in your own bed on a typical night.

Finally, we do not sleep exactly the same night after night. There is some variability in our OSA from night to night. An in-lab sleep test measures what's going on on one particular night with a great deal of accuracy, but whether that particular night is a genuinely typical night is anybody's guess. On the other hand, a home sleep test is often done over several nights, so the sleep it studies is more likely to be representative of your "typical sleep". And hence, for the things a home sleep test can measure with a modest degree of accuracy, the home sleep test may be able to provide a better overall picture of what's going on (in a general sense), even though it will not be able to provide extremely accurate data about the severity of what's going on on any particular night.
(This post was last modified: 11-06-2013 05:26 PM by robysue.)
11-06-2013 05:23 PM
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