(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.