OA without flow limitation?

[NYCzzz]

I'm confused -- on sleepyhead how can i have an "obstructive apnea" without a flow limitation... as detailed below... shouldn't an apnea without any flow limitation be classified as a central?

thanks for your help in understanding this...

[robysue]

I'm confused -- on sleepyhead how can i have an "obstructive apnea" without a flow limitation... as detailed below... shouldn't an apnea without any flow limitation be classified as a central?

Your equipment is listed as a Resmed S9 AutoSet. If you've listed the equipment correctly, the way your machine decides whether to score an apnea as an OA or a CA depends only on the results of the Forced Oscillation Technique (FOT) algorithm and not at all on what's going on in the Flow Limitation graph. If the results from the FOT algorithm indicate the airway is likely to be blocked (obstructed), the apnea is scored as an OA. If the results of the FOT algorithm indicate the airway is likely to be clear (not obstructed), the apnea is scored as a CA.

It is possible for the airway to suddenly collapse without much warning in the sense of significant flow limitations or snoring being present. Sometimes this kind of an obstructive apnea is referred to as a "frank OA" meaning that it came without warning.

An in the data you posted there is evidence of one or two flow limited breaths right before the apnea starts:



The inhalations that I've circled have some evidence of flow limited shape---particularly the one right before the apnea itself. As to why there's no bump in the Flow Limitations graph: It may be that the distortions in the inhalations were not quite bad enough to meet the S9's FL scoring criteria to cause a bump on the FL graph. Or it could be that there was not enough of them in a row for the S9 to decide to increase the value in the FL graph. Like everything else with our machines, the algorithm used to score FLs is not perfect and is not going to pick up every single minor flow limitation.

[palerider]

Or it could be that there was not enough of them in a row for the S9 to decide to increase the value in the FL graph. Like everything else with our machines, the algorithm used to score FLs is not perfect and is not going to pick up every single minor flow limitation.

I seem to remember reading somewhere that the FL (as with many things) is a moving average over several (5?) breaths, so one or two probably wouldn't show up.

[archangle]

I think some people's "throat apnea valve" tends to flap shut all at once on exhale. I think the air pressure sort of presses the soft palate closed at the back of the mouth.

You can see flow limitations in the airflow graphs as sort of a square wave in the waveform. Sometimes, I go straight into a full apnea immediately from a nice, smooth, sinusoidal breathing pattern.

i.e. Some people go directly into obstructive with no previous "flow limitation."

[avi123]

On my S9 I get this for Flow Limitation (FL) these days:



In April 2011 I had this for Flow Limitation which was really bad:



To diagnose FL the S9 checks the flatness of the respiration curve and assign an out of roundness weight level (Scale) to it like this:

{This has nothing to do if the machine diagnoses or not OA and/or CA}





You can see here how my S9 raised the FL graph b/c of flatness of the tops of my respiration curves: