What is Flow limitation?

[N6CRV]

Hello, I have been running my machine in Cpap mode. But thought I would see what it would do in the Auto mode. I was using a pressure of 8 so sat it to go from 7 to 10. Now when I view my report I see that flow limitations show up. The thing is what do they mean? It is running at a 90% of 8.8 and I get more Hypopneas same as before. Thanks for the help!
Don

[elader]

a breath with a tidal volume some percentage under your average. E.g. a shallow breath.

[N6CRV]

a breath with a tidal volume some percentage under your average. E.g. a shallow breath.

I thought that was what Hypopneas are?

[rested gal]

I think of a flow limitation as a "hypopnea wannabe." A baby hypopnea in the making.

A hypopnea is a "flow limitation", when you come right down to it. Each manufacturer uses their own definition of how limited the flow has to be (and for how long the flow is limited) before they label it a "hypopnea."

CPAP mode doesn't even look for "flow limitations." That's why you didn't see any flow limitations when running in CPAP mode. The reason CPAP mode doesn't record or mark flow limitations is because there's no need to. The CPAP is still going to chug away at the single pressure no matter what happens.

Flow limitations are an autopap's bread and butter, though. An autopap running in autotitration mode mode looks closely for flow limitations...the subtle signs of airway collapse just barely starting to happen. The autopap will raise pressure when it senses flow limitations, to try to open the airway a little bit better. More pressure to try to correct the flow limited breathing -- trying to keep the limited flow from getting worse. Correcting flow limitations with more pressure is how an autopap tries to prevent those slight flow limitations from becoming hypopneas and apneas.

An autopap moves pressure up (and down) slowly and gradually. It doesn't suddenly jump the pressure upward to deal with events. Yo-yo'ing pressure up and down abruptly could disrupt sleep. So, I think for most people it's good to help the autopap (in auto mode) do its job -- the job of trying to prevent apneas and hypopneas from developing -- by setting the minimum pressure up high enough to ward off most apneas right from the get-go. In other words, set the minimum pressure to be almost like using straight CPAP.

Then set the maximum pressure for a good bit of extra ceiling room up above -- a margin of more pressures available up there to be used if needed. But let the minimum pressure do most of the work.

Just my opinion...and I'm not a doctor or anything in the health care field.

[dsm]

Apneas & Hypopneas are detailed by each vendor as to what they mean on their cpap (they do vary a bit).

Flow limitations are respiratory reductions in airflow that don't meet the criteria for scoring as hypopneas (& thus not apneas either).

As an example if your machine scores a hypopnea as 50% reduction in airflow for 10+ secs. Then anything less than that (less in that it lasts under 10 secs) can be scored as a FL (e.g. the reduction only lasted 7 secs instead of 10).

When added up, if there are lots of FLs, they can be considered a problem. This is especially so if they are caused by any upper airway resistance, which in turn may be causing the sleeper to have to put in extra effort to get air in. e.g. If you have severe sinus, or a deviated septum, or excessive polyps, you may be really working hard to breathe. That effort can put strain on both lungs & heart & over time that is not good.

Cheers

DSM

[rested gal]

When added up, if there are lots of FLs, they can be considered a problem.

I guess it depends on the person. I don't think "lots of FLs" are necessarily a problem for everyone. I think I'd say "might be considered a problem for some people."

[lusoman]

So, I think for most people it's good to help the autopap (in auto mode) do its job -- the job of trying to prevent apneas and hypopneas from developing -- by setting the minimum pressure up high enough to ward off most apneas right from the get-go. In other words, set the minimum pressure to be almost like using straight CPAP.

Then set the maximum pressure for a good bit of extra ceiling room up above -- a margin of more pressures available up there to be used if needed. But let the minimum pressure do most of the work.

And this is what works well for me: I was titrated at 13cm, and have my APAP set to to 10/20. My AI is almost always 0, and my AHI averages around 2-2.5 This is a ResMed machine, so I understand the equivalent AHI figure reported by a Respironics would be around 1-1.2.

The pressure rarely varies outside the range 11.6-12.0cm

Just my opinion...and I'm not a doctor or anything in the health care field.

That may be the case, but you are renowned for dispensing oodles of good advice...

[N6CRV]

Hello, THANKS for the great reply's!
Don