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+--- Thread: [Pressure] OA without Flow Limitation? (/Thread-Pressure-OA-without-Flow-Limitation)
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OA without Flow Limitation? - lessgroggy - 01-06-2025
I'm a relatively new APAP user of 3+ weeks but not yet a month, and started using OSCAR a few days ago.
Today my machine and OSCAR declared that I had two obstructive apneas, but to my puzzlement they were without accompanying flow limitation. Is that right? What does this mean?
Two nights ago I had two OAs but I could see the corresponding increase in flow limitation during that time.
Each time inspiration time increased a lot during those intervals. But how can I have obstructive apneas without flow limitations? Any suggestions? screenshot attached.
RE: OA without Flow Limitation? - staceyburke - 01-06-2025
Flow limits ARE apnea they are just not long enough to be counted in the AHI. If a FL is longer than 10 seconds it is recorded as an H or O.
RE: OA without Flow Limitation? - lessgroggy - 01-06-2025
(01-06-2025, 02:57 PM)staceyburke Wrote: Flow limits ARE apnea they are just not long enough to be counted in the AHI. If a FL is longer than 10 seconds it is recorded as an H or O.
Please read my post more carefully. It is saying I had an OA event but the graph at those intervals are recording ZERO flow limitation. I thought you had to have flow limitation for it be obstructive apnea?
RE: OA without Flow Limitation? - G. Szabo - 01-06-2025
Flow limits are calculated by algorithms that assess the shapes of (primarily) the inhalation peaks. The outcome is a relative number describing the degree of difference between the "ideal" and the actual peaks. When no distorted inhalation peaks exist before a complete inhalation blockade, i.e., a "hard" OA, the FL number stays close to zero.
Nevertheless, you did have FL before your OA on the chart.
RE: OA without Flow Limitation? - staceyburke - 01-06-2025
My understanding is a flow limit would be a FL until it becomes classified as a H event or an O event. When it becomes an O or H it is not going to show up as a FL also.
RE: OA without Flow Limitation? - G. Szabo - 01-06-2025
I stick to the explanation I suggested above about FL. Your interpretation aligns with mine because when you have a full-blown obstruction, there is no peak; hence, the FL is not calculated, and the FL and OA (or H) are not counted twice.
The FL figure is tricky. For instance, I have nasal congestion that develops over time and gradually decreases the inhalation (and exhalation) peak volume. Still, it usually does not disturb the inhalation peak's shape, so my FL figure is fine. This congestion makes the peaks even more smooth. However, I have severe flow limits during this period because my oxygen saturation drops. Eventually, the inhalation volume becomes so low that I have a recovery breathing. Interestingly, no OA or H is reported either. Hence, FL is not able to take into consideration the diminishing inhalation volume. It is because everybody's inhalation volume is different. The algorithm only scrutinizes the shapes. Hence, it is advisable to manually check the flow rate patterns from time to time given at good AHIs.
RE: OA without Flow Limitation? - lessgroggy - 01-06-2025
I don't understand what either of you are saying. Two nights ago I also had 2 OA events but as you will see from the attached screenshot from 2 nights ago, the increased flow limit during those flagged OA intervals are clearly visible. Why would this increase in flow limits show up one night and not the other? The waveforms in the events between the 2 nights don't look substantially different to me.
What makes these events conclusively OA and not central apnea? My SpO2 did not drop during either incident last night, in fact weirdly it *increased* slightly.
RE: OA without Flow Limitation? - SarcasticDave94 - 01-06-2025
The flow rate flat line during the Apnea is Obstructive based. The beginning/leading edge of the event is an exhale not inhale. Typically a Central based event occurs after an inhale.
Your pressures set seems a bit low to me, at 4.4 - 6.0. If you added some minimum pressure you can begin adding EPR which allows therapy to be much like the more expensive bilevel.
RE: OA without Flow Limitation? - lessgroggy - 01-06-2025
Well, that doesn't track with my waveforms either because if you look at last night's graph, one of the OAs appears to begin mid-exhalation and the other begins mid-inhalation.
You're right that my pressures are low, and I have already increased them for tonight. When I first started my therapy I did have EPR set at 1 as prescribed, but because I was getting central apnea I'd been advised by my clinician to eliminate the EPR and I also experimented with lowering the pressures because of my discomfort.
But I'd already decided earlier today to try reinstating this EPR for tonight because I'm getting discomfort in my chest even at these pressures, and to increase both the min and max pressures by by 0.8 cm or so tonight with the EPR on and see how that goes.
I have a theory that having the EPR on while starting at a bit higher pressure may make it more likely that an incipient OA waveform might be more formed (give my waveforms more amplitude to begin with) and thus more reliably detected before it become a "hard" OA so that the machine will more quickly increase pressure if needed. If tonight succeeds in not causing my central apnea to return in a really bad way, going forward I'll likely continue to incrementally tick up the max pressure until all the OAs are gone.
RE: OA without Flow Limitation? - SarcasticDave94 - 01-07-2025
The chart you included was what I based my observation. Both events begin on the exhale area, as in below the red zero mark on the flow rate graph trace.