Can someone explain exactly what flow limitation is?

[theres126]

And what I should be looking for in sleepyhead? 

Thanks

[Gideon]

Flow Limitation is a breath where the flow is reduced, but not as much as an Apnea (80-100%), or a Hypopnea (50-80%).

http://www.apneaboard.com/wiki/index.php...limitation

[theres126]

Flow Limitation is a breath where the flow is reduced, but not as much as an Apnea (80-100%), or a Hypopnea (50-80%).

http://www.apneaboard.com/wiki/index.php...limitation

I was reading on one post where they were saying that the flow limitation was flat on top, so showed mouth breathing. How does that relate? Just not sure what I should be looking for in my results. And how flow limitation had to do with pressure as well........ I'm confused.  I was thinking that was the definition of a RERA, not flow limitation?

[Gideon]

Definition of a RERA is a series of Flow Limitations that end in arousal. so the two are definitely related.
Though Flow Limitations may be obstructive, that is not a requirement.  And to my knowledge, they have nothing to do with mouth breathing since they may be of any cause and are defined simply as a reduction in flow.  The waveform typically has either a flat and/or sloped top but may also not have these features and simply be a smaller breath.  Sometimes the waveform is referred to as flattened.

The easiest way to look at flow limitations is to look at the Flow Limitation chart which I understand to be a flattening index (0 to 1).  Sometimes Flow limitations are so consistent that they are not recognized because they look very nearly like normal breaths.

[alexp]

Flow Limitation is a breath where the flow is reduced, but not as much as an Apnea (80-100%), or a Hypopnea (50-80%).

http://www.apneaboard.com/wiki/index.php...limitation

I was reading on one post where they were saying that the flow limitation was flat on top, so showed mouth breathing. How does that relate? Just not sure what I should be looking for in my results. And how flow limitation had to do with pressure as well........ I'm confused.  I was thinking that was the definition of a RERA, not flow limitation?

The graph showing the mouth breathing is the leak rate graph while the one showing flow limitations (and therefore  the RERA) is the flow rate graph.

[sheepless]

to try to restate some of what's been said already: flagged and unflagged flow limitation may appear flat, jagged and/or downward sloped at the top of the 'curve' of inspiration in the flow rate graph. sometimes it may show less amplitude than other breaths, appearing lower above the 0 inspiration/expiration line than non flow limited breaths, with or without the top-of-curve distortions.

in the flow rate graph, mouth leaks can show up as a reduced amplitude inspiration curve and with a non-ffm there may be less to no amplitude (in comparison to inspiration) visible below the 0 inspiration/expiration line. I'm not sure about the ffm but suspect the latter is not characteristic of mouth breathing using a ffm.

I can see how the reduced amplitude inspiration curve might suggest a leak but not necessarily a mouth leak. I don't think the flat top inspiration curve (indicative of flow limitation) has any relationship to mouth leaks.

[Stom]

And what I should be looking for in sleepyhead? 

Thanks

There are different issues in play. Flow limitations are defined by the CPAP makers as part of their auto adjusting pressure. The flow limitation flags you see in Sleepyhead/OSCAR are flagged by the machine using the makers algorithm and displayed by Sleepyhead/OSCAR. Sleepyhead does not do it's own flagging of flow limitations.

So, the flow limitation flags will vary based on the math used by your CPAP company, and can vary from model to model.

ResMed also determines flow limitation. S8 AutoSet defines flow limitation using flatness of an inspiratory breath. The flatness index is calculated by the RMS deviation from unit scaled flow calculated over the middle 50% of a normalized inspiratory breath.4 From the S9 onward, flow limitation is calculated using a combination of flatness index, breath shape index, ventilation change, and breath duty cycle. Ventilation change is the ratio of the current breath ventilation to recent 3-minute ventilation. Breath duty cycle is the ratio of current breath time of inspiration to total breath time of recent 5 minutes. If a breath is severely flow limited, the flow limitation index will be closer to one and when the breath is normal or round, the flow limitation index will be zero.8

-Treatment of sleep-disordered breathing with positive airway pressure devices: technology update, Karin Gardner Johnson, Douglas Clark Johnson, Medical Devices, 2015

You can find this paper online.