Distinguishing OA from Positional Change
As I try to tune my CPAP therapy I've started taking a careful look at my OAs. I've begun collecting SpO2 levels and it makes me wonder if all my reported OAs have clinical significance.
I've included a thumbnail of one that I question. A 14 sec OA was flagged at 01:17:51. Over the entire interval from 01:15 to 01:21 SpO2 drifted from 93 to 94. It was 94 at time of OA and essentially unchanged 3 minutes later. I see a drop in ventilation at the exact time of the OA. Is my Dreamstation actually spotting an treatable obstruction in my airflow or is this likely to simply be associated with a positional change while sleeping? Note that pressure was unchanged throughout this interval.
Thanks.
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RE: Distinguishing OA from Positional Change
Don't know the answer on if it was a positional change or not. I do know that the Dreamstation won't raise pressure based on a single event.
RE: Distinguishing OA from Positional Change
It is quite hard for me to figure out what the Dreamstation is thinking.
Here's a screenshot. CPAP use starts at 23:21. There are no events at all until a CA at 00:20 yet there are five pressure increases initiated and then aborted. The first pressure increase that persists occurs at 01:15 after 1 CA 6 Hypopneas and 1 RERA. So 5 of 6 pressure increases during this period were based on no events, and one was triggered after 7 events.
It is possible that the five pressure increases were based on clever machine judgments based on respiration rate and tidal volume, and that these judgments were not encoded as specific events. However, during the entire time period that the Dreamstation was busy making pressure adjustments SpO2 was under control in the range 94 +/- 1 and the variations in SpO2 seemed completely unrelated to its pressure adjustments. I realize that Dreamstation does not have the SpO2 data, but with the benefit of this data its heuristics appear a bit unreliable.
Thanks
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RE: Distinguishing OA from Positional Change
Normally from what I've seen pressure will increase to flow limitations and snores. Also when you have two or more obstructive events within a certain time frame. Not sure but I think it's 5 minutes on the time frame. Pressure will normally reduce due in response to a clear airway event.
One of the advantages of the Resmeds over the dreamstations is you can see on a plot graph the flow limitations rising and falling. Dreamstations only show flow limitations as an event. I have no idea how bad the flow limitation has to be for it to register as an event. You also have no way of seeing how the pressure rises in response to flow limitations.
RE: Distinguishing OA from Positional Change
I followed one of your links to the Sleepyhead beginners guide and found an answer there. The 5 increases with no events were part of the Dreamstation design. I am not concerned about waiting for multiple events to act.
Quote:The Philips Respironics System One also has a "search" routine built into its Auto algorithm, and it will periodically increase the pressure as a "test" to see if the shape of the wave flow improves, even if nothing is being scored. Those test increases show up as saw-teeth on the pressure curve.
RE: Distinguishing OA from Positional Change
Glad you found the Beginner's Guide to Sleepyhead. The five pressure increases are a normal part of the Respironics auto algorithm which will increase pressure 1.5 cm over two minutes to "test" the higher pressure. Normally these pressure increases and decreases are not felt by the user, but it gives the pressure a "hunt and peck" appearance. The truth is, I have no love for the Philips Respironics auto algorithm and find it is far less effective for most people, as pressures respond to events rather than act proactively to stop them. Your hypopnea is typical of people using these machines, and would likely mostly disappear with a Resmed Autoset and using EPR, which is a limited bilevel form of therapy. Between the pressure responsiveness and EPR you would be surprised at the difference.
RE: Distinguishing OA from Positional Change
I only consider a true OA event to be:
The flow rate flatlines at end of exhalation, and take longer than 10+ seconds to begin inhalation again. Since airway collapse occurs at end of exhale/Beginning of inhalation.
So any wave form where
A) it goes from exhale to 10+ sec flatline to exhale is not an OA.
B)Similarly from inhale to 10+ sec flatline to inhale is not an OA.
C) from inhale to 10+ sec flatline to exhale is not an OA.
These 3 cases are most likely a holding of breath while changing sleep position imho.
RE: Distinguishing OA from Positional Change
Based on that, would I correctly interpret the event as a probable positional change? Since the bulk of the graph area adjacent to the OA is above the zero line it looks to me like the OA flat line was framed by two net inhalations. What do you think?
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RE: Distinguishing OA from Positional Change
Even at the hospital, a change of oxygen by 2 units is a big nothing unless it's sustained. It still might not be clinically significant (i.e. a non-problem). When my Mom was recently hospitalized we had a discussion with the doc over that. I have roughly the same number of OA's as yourself. Any where from 2-8 per night. The only time it is of concern is when the OA is prolonged. So long as they don't last beyond 20 seconds, the doc isn't concerned. If they start lasting longer than that, I need to get re-evaluated. But, they've been that way since I started cpap.
