Flex settings and hypopneas

[KSMatthew]

How does a Dreamstation flex setting affect hypopneas?

At constant and 7cm my AHI numbers had been rising from 1.4 +/- to 3.5 +/- over the last 4-6 months. It was time for a change in settings, I'd been on that setting for > 10 years.

I moved from fixed pressure (7) to auto (7-9) about 2-3 weeks ago. Flex was ON and set to 1. From the Sleepyhead graphs that flex setting corresponded to a 2cm pressure relief on exhale. With those settings my AHI numbers rose from around 3.5 (mostly hypopneas) to 6+ with almost all hypopneas. And my 90% pressure was 9.

Last night I turned off flex and saw a big difference this morning. 90% pressure was 8 and AHI was around 1.6.

I know, this was just one data point. But it was a big swing, and the only thing that I changed was Flex by turning it off. That meant I was exhaling against full pressure vs exhaling against a -2cm pressure. I haven't downloaded into SH yet, but I'm assuming the hypopneas were much lower last night.

[Sleeprider]

Flex is confusing to most people. Regardless of the setting 1-3, you get up to 2-cm pressure relief, but the transition is either faster (1), or slower (3). The actual pressure relief is proportional to the force, or flow rate of your own exhale. So people with good respiratory function and tidal volume seem to see the most pressure relief. Because it is flow based, as your exhale slows, the pressure rises back to IPAP by the time you complete exhale, and you have full IPAP pressure when you begin inhaling.

EPR on the other hand is an implementation of bilevel, and actually gives you the amount of pressure relief 1-3 cm, that you set. It is initiated by your breathing, but follows, rather than leads. So as you begin exhaling, the pressure drops to EPAP, and does not return to IPAP until you spontaneously initiate the inhale...got it?

Sensitivity to any pressure relief scheme is purely individual in the perception of comfort, and sometimes in the manifestation of central apnea. There could be any number of reasons, the point is some people have CA and most do not. If you do, then Flex or EPR may not be for you. Sometimes EPR will work for someone sensitive to Flex and vice versa. Go figure...

[KSMatthew]

Thanks for the Flex explanation. It makes sense.

I was really surprised to see such a big drop in hypopneas by turning it off. My aprnea index is normally less than 1, but the hyponea index is what's been causing my total AHI to rise.

Note: I edited my original post. I had been using inches instead of cm for pressures. I knew it was cm, but had "inches" on my brain for some reason.

[BigWillyAus]

Flex is confusing to most people. Regardless of the setting 1-3, you get up to 2-cm pressure relief, but the transition is either faster (1), or slower (3). The actual pressure relief is proportional to the force, or flow rate of your own exhale. So people with good respiratory function and tidal volume seem to see the most pressure relief. Because it is flow based, as your exhale slows, the pressure rises back to IPAP by the time you complete exhale, and you have full IPAP pressure when you begin inhaling.

I can't thank you enough for that explanation,been trying to get my head around it.

I also suffer from a lot of hypopnea's I have Flex set to 3 should I change to 1 or turn it off all together as well?

[Sleeprider]

As long as it it enabled, the 2-cm pressure relief is enabled, only the speed of transition changes. Turn it off if you want no change in inhale/exhale pressure. Oddly, a lot of us did bebber with a setting of 1, even though it still provides pressure relief.