Is there something screwy with ResMed flow limitations?

Ok, I've been puzzled about the flow limitation data being reported from my A10. Here's a little sample, of a cluster I had last Monday:

So looking at the Flow Limitation graph aligned with the Flow Rate graph, there is the hypopnea, which is aligned with a rise in the FL. But then there are the three obstructive apneas. The FL graph shows zero flow limitation during those. Really?!? An obstruction that causes breathing to stop doesn't qualify as something called a "flow limitation"?

Maybe "flow limitation" is some term of art which isn't just the airflow being limited but some more subtle thing? Or maybe the machine can't measure flow limitation during obstructive events, and it should be reporting "no data" rather than zero for these periods?

Anybody know what's going on here? I know that the PR machines don't report the thing that they call "flow limitations" in the same way...

cathyf wrote:So looking at the Flow Limitation graph aligned with the Flow Rate graph, there is the hypopnea, which is aligned with a rise in the FL. But then there are the three obstructive apneas. The FL graph shows zero flow limitation during those. Really?!? An obstruction that causes breathing to stop doesn't qualify as something called a "flow limitation"?

no, it's not a flow limitation. if there's no flow, (apnea) then there can't be a limitation of that flow... can't limit nothing

a flow limitation is a flattening of the normal bell curved shaped of the inspiration part of the respiration cycle, you'd need to zoom in more, and you'll see where the FL graph kicks up, your inspirations (part of the flow trace above zero) isn't rounded, it's flattened.

watch:https://www.youtube.com/watch?v=-gie2dhqP2c

Ah, yes, that makes sense. Having watched the video, what confuses me is that my breathing never ever looks anything like that smooth even sine wave. Here's a closeup of that hypopnea.

I see that characteristic shape, but I'm still not sure that I'm really getting this -- over at 23:34:25 or so there is a curve that looks like the FL shape, but it's not flagged that way.

I guess this is a lot more subtle...

cathyf wrote:Ah, yes, that makes sense. Having watched the video, what confuses me is that my breathing never ever looks anything like that smooth even sine wave. Here's a closeup of that hypopnea.

I see that characteristic shape, but I'm still not sure that I'm really getting this -- over at 23:34:25 or so there is a curve that looks like the FL shape, but it's not flagged that way.

I guess this is a lot more subtle...

that's one place that video fell down, what they showed wasn't typical sleep breathing.
your *awake* breathing often looks more like a sine wave, however, asleep breathing is generally more of a smooth inhale, followed by an abrupt exhale, which tapers to nothing, and a short pause.

what you have between 22:30:30 and 22:34:00 on the trace looks pretty good.. (the FL trace lags behind the actual breathing by a few seconds, I believe, since it is an average of a number of breaths.) you see a very low FL amount a few seconds after that segment.

you can see the almost chair shape of the inhalation at the beginning of the trace, that's pretty severe flow limitation, you start to inhale, and then it gets restricted for the rest of the inhalation.

you can turn on a zero line in the flow trace to help see what's above and below 0 flow. right click on the left vertical scale.

The graph shows pretty classic FL. The event flag occurs only after a series of flow limited breaths have occurred that drop your respiratory volume below whatever level the machine algorithm is programmed with to set a flag. So each flow limited breath is not flagged, but rather a period of flow limitation.

Flow limitation is an obstructive event like an incomplete apnea, and you often see a hypopnea or RERA flagged when it occurs. If it is a frequent feature of your sleep, a higher pressure, or even bilevel pressure support is usually effective in minimizing flow limitation. During the period in your screenshot above, you were at the maximum allowed machine pressure. If you want to see if additional pressure can suppress FL, then you might consider increasing maximum pressure above 14 cm.

Sleeprider wrote: The event flag occurs only after a series of flow limited breaths have occurred that drop your respiratory volume below whatever level the machine algorithm is programmed with to set a flag.

it sounds like you're confusing flow limitations with hypopneas, also, resmed doesn't have an event flag for FL, it has a severity chart. you can have the consistent respiratory volume along with severe flow limitations, it just is harder, and takes longer to inhale. flow limitations != hypopnea.

Sleeprider wrote:Flow limitation is an obstructive event like an incomplete apnea, and you often see a hypopnea or RERA flagged when it occurs.

this is incorrect.

I do agree that increased pressure is the proper response to curb flow limitations.