Why does EPR help with flow limitations?

[cathyf]

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.

After two months on the Air-11, I'm wondering if the difference between Air10 and Air11 is that the Air11 appears to do EPR as PS of 3, with all of the other timing and sensitivity settings running as the Aircurve defaults.

It looked to me like the Air10 EPR was running at a VeryHigh trigger sensitivity.

My flow limits on the Air11 look a lot more like the flow limits on the vauto. While I do better at PS of 4, PS of 3 is not very different, so the Air11 is looking pretty good.

(I'm also wondering if the "For Her" and/or the "Soft Response" algorithms are a second and third group of timing and sensitivity settings.)

But anyway, the EPR of the original Air10 which I have looks like it might have been implemented by engineers who weren't on speaking terms with the engineers who built the Aircurve. (Which is pretty scary!)

[Geer1]

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)?

IPAP does not provide mechanical assistance.  

There are two main variables in PAP/ventilation. As you noted EPAP is constant pressure that is used to maintain an open airway. It provides minimal assistance during inhalation and it actually makes it more difficult to exhale because you have to breath out against the pressure. PS is what provides the majority of mechanical assistance by increasing the pressure differential during both inhalation and exhalation. 

Treating flow limitations is always a two step process. Step 1 find EPAP that maintains an open airway majority of the time. Step 2 provide assistance with EPR/PS as necessary to overcome remaining flow limitations.

[pholynyk]

Step 3 - Make sure the Central Apneas don't increase too much

[WakeUpTime]

Step 3 - Make sure the Central Apneas don't increase too much 

Good point.  That's always been the big one for me.  For others with CAs issues, they should also watch the negative impact of increasing EPR/PS.  I like the comfort of a higher EPR/PS, and a BiPAP, but it brings my CAs way up.  I wish I understood that years ago.  It's that struggle and balance of managing CAs, Aerophagia, comfort, etc.

[Sleepster]

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)?

It makes it harder to exhale when the EPAP is higher. You have to exert more effort to achieve the same flow rate during exhalation. If you fail to exert this extra effort it will limit the flow.

[Geer1]

Although step 3 above doesnt help treat flow limitations it is important in treating sleep disordered breathing as a whole.

The reality is that not all flow limitations are issues and must be treated. The same can be said even about more severe events like hypopnea and apnea. A flow limited breath on its own is rarely an issue. Flow limited breaths are usually only an issue when they are occurring often and causing excessive respiratory effort causing arousals (RERAs) disrupting sleep.

Similarly the odd paused breaths or central apnea is not usually an issue on its own either. It is when they occur too often and start disrupting sleep regularly that they become an issue.

Reras for the most part act in the opposite way of a central apnea. A rera is usually caused by too high a co2 level whereas central apnea is usually caused by too low co2. If you arent prone to central apnea but start having them after raising ps it is a sign you have gone too far (at least until body adapts to the higher ps/lower co2). If your are prone to both flow limitation and central apnea then it becomes much more difficult to try to treat the flow limitations and simply increasing ps/epr is unlikely to help. Other treatments like addressing positional aspects (to avoid flow limitations rather than try to treat them) or stepping up to a machine like asv is likely required. That said many of these patients do not seem to get relief from symptoms even on asv when flow limitation and central numbers are low. I think this is due to the patient wrongly assuming/hoping the symptoms are due to sleep disordered breathing.

[dundematon]

I been using airensense 10 since 2017 and EPR has always been on 1. Flow limitations have been constant averaged around 0.08-0.11 maxed 0.5 every night. Pressure setting has been most of these years min 6 and max 12 --> for the past year resulted pressure avg ~8 and 90% ~9. Now I increased the min pressure to 8.4 and set the EPR to 3. What happened? All the flow limitations disappeared for the first time and needed max pressure peaks dopped from 11 to 9.5 (also 90% pressure avg dropped). AHI has basically been always 0 - only few false flags from position changes --> AHI 1. Leaks also totally dissapeared with EPR - they weren't much of a problem anyway execpt drying mouth (90% leak rate has always been 0) - apparently exhalatiion related. 

I still have lot of "sighs" or "gasps" every 4-6 minutes even in deep sleep - sleep disturbances RERAs? european machine doesn't flag them. Nrem used to be like I was in coma but everything is more like zigzag. Cause: chronic cervical and thorasic pain - taking amitriptyline/chlordiazepoxide + nsaid every night. Otherwise I can sleep only 4 hours because of the pain - with the drugs I can sleep 7-9h.

It's funny that all the youtube sleepdiagnostigs recommend not using EPR. Also I have written previously here that losing weight over 45kg to so called normal weight didn't have any effect on on the situation or actually I need more pressure now than before the weight loss.

[chemmkl]

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)?

If you have a ResMed machine, I think this video explains it pretty well: https://www.youtube.com/watch?v=GaXA0ZIWj1Y
It's based on this scientific paper: Zhu, Kaixian, et al. "Pressure-relief features of fixed and autotitrating continuous positive airway pressure may impair their efficacy: evaluation with a respiratory bench model." Journal of Clinical Sleep Medicine 12.3 (2016): 385-392.

So essentially on ResMed machines when you enable EPR in AutoSet they increase the inspiratory pressure significantly more than when EPR is off in order to keep the apnea under control due to the algorithms they have for Auto CPAP (this does not happen with similar EPR systems from other manufacturers). So if your maximum pressure to keep your airway open is around 12cmH2O without EPR, with EPR is going to be around 14cmH2O. This explains why just enabling EPR helps with inspiratory flow limitations: is using higher pressure. At the same time, because now you respiratory support is higher (14 inspiratory, 11 expiratory if you have EPR set to 3cmH2O) the pressure differential increases the flow of air out of you lungs keeping your airway open for the regular obstructive apneas as well.

[Gideon]

Look at titration protocols

Exhale pressure is what manages OA events

Differential pressure between exhale and inhale is what manages hypopneas, flow limits, RERAS and UARS. This is EPR/PS.

If your CPAP pressure is at the point where OA events are just managed and you add EPR you need to adjust pressure up by the amount of EPR to maintain the same control as without EPR. The practical side of this is that most have their CPAP pressure higher than that and thus they do not need to adjust, if they need an adjustment it can easily be made after EPR is implemented.

[meatwagon42]

It makes it harder to exhale when the EPAP is higher. You have to exert more effort to achieve the same flow rate during exhalation. If you fail to exert this extra effort it will limit the flow.

He is talking about how it reduces inspiratory flow limitations not expiratory flow limitations.