Why does EPR help with flow limitations?

[breathestopbreathe]

Does anyone have an explanation for why EPR can improve flow limitations?  I can’t quite wrap my head around why this is the case and haven’t found a real explanation.  EPR doesn’t seem to help with obstructive apneas, but EPAP at an appropriate minimum pressure obviously does.  As flow limitations are basically just very minor obstructions, why isn’t an EPAP that prevents OAs also sufficient to prevent flow limitations? And what is the physical basis for EPR helping flow limitations (but not helping OAs)?

[kappa]

Yeah... I'm with you on this. Still trying to get my head around it, complicated by other commentators suggesting that EPR is often not a good idea.

My thought is that "Flow Limitations" (in a ResMed context) are a heuristic algorithm that gives a number output based on the flatness of the inhalation flow rate peak. EPR adds a sawtooth pressure wave that is triggered by inhalation and this will tend to make the inhalation flow rate waveform less flat than it would otherwise have been (increased pressure during the saw tooth EPR leads to increased flow rate). Hence the "flow limitation" number will be lower.

This may reduce the pressure response (ResMed increases pressure based on FL) and hence the max pressure may be lower.

[Sleeprider]

EPR is an implementation of bilevel pressure that is nearly identical to the Aircurve machines, but limited to 3-cm. It assist inspiratory flow limitation by bringing "pressure support" behind the spontaneous effort of the user, which is effectively a mechanical assist that helps to mitigate airway resistance, resulting in a more normal breath profile. In general, it helps to shorten inspiratory time and reduces effort to achieve normal tidal volume. It does not work equally for everyone in all cases, and does not have the timing and sensitivity settings available on the Aircurve. Compare charts of an Aircurve and Autoset, and it is clear that the IPAP/EPAP wave pattern is identical.

[Nightynite]

Thanks Sleeprider. In my case I find I have less centrals on EPR 2 than EPR 3. I guess it’s strictly an individual treatment situation. I have never tried 1 yet, cause I was happy on 2.

[Gideon]

Smaller EPR or PS settings tend to decrease CO2 driven central apneas because less of your CO2 is flushed from your system

[Geer1]

Imo it is fairly simple.

Flow of air/liquids is caused by differential pressure, not pressure alone. An easy analogy is a balloon, if you pressurize it there is no flow but if you release the nozzle so there is a pressure difference (pressure inside balloon, no pressure outside of nozzle) then air flows out.

Epr is a pressure differential. It increases the pressure differential when breathing in and also when breathing out. More air flows easier reducing effort and flow limitations (which are just slightly reduced flow rate periods). The increase of pressure also happens during inhale which helps keep pressure in your airway more constant/increasing (since your muscles actually cause lung volume to increase which draws a vacuum inside lungs and pressure in your airway varies from a vacuum in lungs to machine pressure at machine).

Anyways that is how a mechanical engineer believes this works.

[DaveCar]

Smaller EPR or PS settings tend to decrease CO2 driven central apneas because less of your CO2 is flushed from your system

Is that because of the higher average standing pressure, or because of a slower/less complete exhale ?

[Gideon]

The larger difference promotes a fuller breath which results in an equally large exhale.

[Geer1]

Is that because of the higher average standing pressure, or because of a slower/less complete exhale ?

Higher pressure differential = more airflow out = lower CO2 levels.

Conversely lower epr/ps = higher CO2 levels and therefor fewer central apnea.

[breathestopbreathe]

Thanks for the response. I still find this a little unclear.  Let’s say I have no flow limitations with settings IPAP = 8 and EPR = 3. I then turn EPR off. Why may I have inspiratory flow limitations now even though my IPAP is the same, providing the same amount of mechanical assistance to increase tidal volume, shorten inspiration duration, and prevent the airway from collapsing during inspiration (as only the EPAP has changed)?