Can someone explain how EPR reduces flow limitation?

[obstructedairway101]

Curious to understand how epr works specifically on flow limitation?i see alot of people talking about adding epr to decrease flow limitation guess I don't see how reducing expiratiratory is supposed to help decrease flow limitation can someone explain ?

[SarcasticDave94]

It's the pressure differential between exhale and inhale, this action makes your CPAP a bilevel. And EPR will act just like pressure support in the bilevel.

[Deborah K.]

For most people, EPR makes breathing more comfortable too, as it allows longer exhalation, which is more natural breathing for most folks.

[PeaceLoveAndPizza]

To add to Dave and Deborah’s responses, I have been pondering that when there are physical issues in the airway dropping pressure on exhalation makes it easier to exhale which reduces the flow limitations from pushing against too much pressure. Too little pressure differential and there is no improvement, and too much differential allows you to expel CO2 too completely which causes different issues. The trick is to find the correct amount of pressure and pressure support, which requires experimentation.

SleepRider is very knowledgeable about this topic and may want to add something we missed.

[Dodies]

Personally, I saw a load of CA's with EPR set to 3, changed it to 2 and saw an improvement, and I dont realy understand why..

[obstructedairway101]

Makes sense thanks all for your reply

[PeaceLoveAndPizza]

Personally, I saw a load of CA's with EPR set to 3, changed it to 2 and saw an improvement, and I dont realy understand why..

That is typical of  too much pressure support causing CA’s. They possibly would abate over time depending on whether treatment emergent or not.

[Sleeprider]

EPR is a form of bilevel pressure support. In the mask pressure chart, it looks identical to the pressure delivered by the Aircurve Vauto, but limited to a maximum of 3-cm. Flow Limitation is correctly termed "Inspiratory Flow Limitation", and it works by supporting or supplementing the spontaneous respiratory effort during inspiration. This overcomes the tendency of the airway to collapse during inspiration by providing proportionally higher pressure as a breath progresses to it's peak flow. Inspiration occurs because the chest expands creating negative pressure in the upper airway (vacuum), and this is the mechanism of flow limitation and obstructive apnea. Without pressure support, flow limitation in some individuals is proportional to inspiratory flow, due to increasing thoracic pressure as inspiratory progresses to its peak. This is easily visualized on the flow rate graph in Oscar as a flattening or declining flow rate, even as respiratory effort increases. Pressure support offsets this vacuum and prevents occlusion of soft tissue in the upper airway. The lower pressure during exhale (cycle) is not especially important to flow limitation, but without the pressure reduction, there would be no ability to have inspiratory pressure support. This lower pressure makes expiration easier, but exhale is basically a passive activity, and the muscles do not engage to cause it. The airway is under positive pressure during exhale, and expiratory obstruction is relatively rare, with some exceptions like palatal prolapse.

EPR is another name for pressure support and in my opinion places an inappropriate emphasis on the reduced pressure during expiration, when the real benefit is, exactly like bilevel, pressure support during the inspiratory phase. The use of EPR is best understood as a pure bilevel implementation, but Resmed avoids that because they are selling "CPAP", and their medical approval of EPR has been ensconced as a "comfort feature". As a result, it is important to establish a minimum EPAP that provides adequate airway patency when inspiration begins (trigger). Many CPAPs, and the theory of V-COM is to restore the CPAP pressure before trigger occurs. This is why Philips and other CPAPs that do not provide inspiratory pressure support fail to resolve flow limitation and the reason why this forum has very strongly advocated Resmed as a better solution...you are getting a free bilevel. The important thing is to disregard that this is a CPAP and to treat it as a bilevel in titration and use.

[Sleeprider]

I would appreciate any input or help in editing the above discussion, and have added it to the Flow Limitation wiki here: https://www.apneaboard.com/wiki/index.ph...Limitation

[G. Szabo]

I would appreciate any input or help in editing the above discussion

Let me add one more thing that was touched only implicitly: When the inspiratory and expiratory pressures are the same during CPAP therapy, the lung cannot be fully emptied during the exhalation period, especially at high pressures. 

When we increase CPAP pressure, this phenomenon becomes increasingly pronounced. Hence, less and less of the lung's volume can participate in the breathing cycle because of the dead air stuck inside. Therefore, inspiration becomes less and less efficient from the perspective of the oxygen/carbon dioxide exchange process, leading to a special kind of inspiration limitation. Hence, paradoxically, a less efficient exhalation leads to limited inhalation or a particular inhalation flow limitation, which we cannot necessarily see on the flow chart.

I could only guess how the lungs or brains might react to this situation. Either the inspiration effort (volume)  or frequency could increase. However, these have limited impact. Therefore, the solution is maintaining an optimized pressure difference between inspiration and exhalation. EPR is a good example of this at an affordable cost.