Isn't Resmed's Expiratory Pressure Relief really Inspiratory Pressure Support??

[Reznik]

In Resmed's EPR (and in all spontaneous bi-level machines), the machine remains at the EPR pressure until you start inhaling again.  Respironics C-Flex (but NOT C-Flex+/A-Flex) does just the opposite.  It returns to the machine's stated pressure as soon as you stop breathing out.  It doesn't wait for you to start inhaling.

Some people get apneas on inhale not on exhale.....

Everything that I've read about titration indicates that EPAP is what prevents obstructions, and that IPAP does not.  Have you read something that says otherwise?

[Sleeprider]

I think Reznik is basically correct on this. The Airsense 10 works the same as an Aircurve 10, but uses different terminology. In Resmed CPAP, the minimum pressure is the minimum IPAP pressure. EPR can reduce that pressure from 1-3 cm below that setting. In Aircurve Bilevel, the minimum EPAP pressure is set, and pressure support is added to make the IPAP pressure. Since obstructive apnea is resolved by EPAP, this means CPAP pressure should be increased proportionally to EPR to keep the same therapeutic value. It can get confusing if you can't do the math both directions, but as long as EPR or PS do not exceed 3-cm, the machines can produce approximately the same results. The EPAP pressure does not recover towards IPAP until a spontaneous inhale is initiated, so any apnea will remain at EPAP or pressure minus EPR. This is the point at which most obstructive apnea will occur due to collapse of the airway. HalfAsleep said some people get apnea on inhale not exhale, and that's true, except the apnea initiates at the transition and inhale never gets started, so with Resmed EPR, you are in the hole of EPAP which may be 3-cm below your prescribed pressure. This is offset in autoset mode because pressure will increase to compensate.

Respironics Flex changes pressure at transition by up to 2-cm proportional to flow, so a weak expiratory flow gets less pressure relief, and a strong exhale gets the full 2-cm. Seems backwards, but that's what it is. The EPAP pressure returns to IPAP before inhalation begins. It has less impact on the prescription, however when in Auto CPAP mode, the Respironics machine is slower to increase pressure to prevent apnea, so it is not uncommon to see hypopnea when minimum pressure is not high enough to compensate for Flex.

What all this means is you need to be aware of the impacts of using EPR or Flex. Expect that with auto pressure, the pressure will be higher than your titrated CPAP pressure without pressure relief. It also means most prescriptions end up being wrong when the end-user enables the comfort features, if those were not part of the fixed, single pressure titration.

[Walla Walla]

Here is how it works. If it is machine caused Central it's because the pressure support is too large allowing the CO2 to be washed out of your lungs. This causes the brain to stop the signal to breath until the CO2 builds up. If you take away the pressure support the centrals will clear up because CO2 builds up triggering the brain to send the signal to breath. With true central the problem is not the pressure setting but the brain not sending the signal due to other reasons. That being the case Bipap's aren't assigned to fix centrals ASV's are.

[Reznik]

Here is how it works. If it is machine caused Central it's because the pressure support is too large allowing the CO2 to be washed out of your lungs. This causes the brain to stop the signal to breath until the CO2 builds up. If you take away the pressure support the centrals will clear up because CO2 builds up triggering the brain to send the signal to breath. With true central the problem is not the pressure setting but the brain not sending the signal due to other reasons. That being the case Bipap's aren't assigned to fix centrals ASV's are.

Hi Walla Walla,

I agree with you, partially.  Having too high of a Pressure Support (or just too high of a pressure generally) can definitely cause centrals by increasing tidal volume too much.  If your tidal volume is too high, you'll have an excess build-up of oxygen and/or low CO2 levels, you'll hold your breath to compensate. However, if you have centrals that result from low respiratory drive, the right amount of Pressure Support can help to prevent them. 

ASV is just a real-time automatic adjustment of the Pressure Support (IPAP minus EPAP).  Auto ASV combines the automatic adjustment of EPAP (i.e., Resmed's Autoset) with the real-time automatic adjustment of Pressure Support that ASV alone provides.  Just a some people with OSA don't need an autoset machine, not everyone with central sleep apnea need an ASV.  For some people with OSA, a CPAP set to the right pressure is good enough.  For some people with central apneas, the right fixed pressure support setting in bi-level is enough, as well.

[Sleepster]

That's why, if you are titrated to CPAP at 8.5 with no EPR, and you decide you want EPR, you should increase the programmed pressure on your machine by the amount of EPR you want.

That depends on what you mean by "should".

If you turn on EPR and it doesn't increase your event indices, but it does make things more comfortable, then I see no reason to raise the pressure.

On the other hand, if you turn on EPR and raise your pressure and it increases your CA index, or makes you less comfortable because, for example, it makes you swallow more air, then I would say you shouldn't raise the pressure.

[Sleeprider]

That's why, if you are titrated to CPAP at 8.5 with no EPR, and you decide you want EPR, you should increase the programmed pressure on your machine by the amount of EPR you want.

That depends on what you mean by "should".

If you turn on EPR and it doesn't increase your event indices, but it does make things more comfortable, then I see no reason to raise the pressure.

On the other hand, if you turn on EPR and raise your pressure and it increases your CA index, or makes you less comfortable because, for example, it makes you swallow more air, then I would say you shouldn't raise the pressure.

I think this is where the auto algorithm comes to the rescue.  Anyone using an auto cpap at default minimum pressure of 4.0 and adding EPR or Flex will experience big problems. If minimum pressure is at least 7.0, most people will get by.  We see it on the forum all the time.  

Similarly, pressure support (EPR) of 3 cm is enough to trigger CA in some people.  For both of these situations, the manufacturer should be including trouble-shooting tips in the user manual for using the comfort features.  That will never happen because any therapeutic direction must come from the doctor, and the manufacturers will not cop to the fact EPR or Flex can affect therapeutic efficacy...it does in some, but not all people.

[Reznik]

That's why, if you are titrated to CPAP at 8.5 with no EPR, and you decide you want EPR, you should increase the programmed pressure on your machine by the amount of EPR you want.

That depends on what you mean by "should".

If you turn on EPR and it doesn't increase your event indices, but it does make things more comfortable, then I see no reason to raise the pressure.

On the other hand, if you turn on EPR and raise your pressure and it increases your CA index, or makes you less comfortable because, for example, it makes you swallow more air, then I would say you shouldn't raise the pressure.

Of course, I agree with both of your statements.  Would you also agree that, if you turn on EPR and it doesn't raise your event indices, then your CPAP without EPR should probably not have been set as high as it was in the first place?

[Reznik]

I think this is where the auto algorithm comes to the rescue.  Anyone using an auto cpap at default minimum pressure of 4.0 and adding EPR or Flex will experience big problems. If minimum pressure is at least 7.0, most people will get by.  We see it on the forum all the time.  

Similarly, pressure support (EPR) of 3 cm is enough to trigger CA in some people.  For both of these situations, the manufacturer should be including trouble-shooting tips in the user manual for using the comfort features.  That will never happen because any therapeutic direction must come from the doctor, and the manufacturers will not cop to the fact EPR or Flex can affect therapeutic efficacy...it does in some, but not all people.

The machine mins out at 4.0, even with EPR.  So, for example, if they set EPR to 3.0 and start at 4.0, EPAP stays at 4.0 and they get no OSA benefit until the pressure on the machine hits 7.0.  Before 7.0, they're only getting an IPAP increase.  After 7.0, both IPAP and EPAP increase together.  But, this is something that's not obvious because they call it "expiratory pressure relief."

With respect to 3cm being enough to trigger CSA, I'm finding myself in the opposite situation.  With pressure support of zero, I get CSR with Central Apneas.  But, with pressure support of 3, the hypopneas right before and after the CAs never happen, the CSR mostly levels out, and the Central Apneas never happen.  Until I realized that I really had a Bipap machine and that EPR was lowering my EPAP, the behavior didn't make any sense.

Of course, like with everything, your mileage may vary.  If the EPAP is too low, you can experience obstructive apneas.  If the EPAP is too high, you can get centrals.  If the pressure support is too low, you can get hypopnea and centrals.  If the pressure support is too high, you can get centrals.  

It seems that we're all looking for the goldilocks zone.

[Walla Walla]

Reznik,
I've never heard of increasing pressure support to erase central apnea. Could you post some before and after charts so I can see this?

[Sleepster]

Would you also agree that, if you turn on EPR and it doesn't raise your event indices, then your CPAP without EPR should probably not have been set as high as it was in the first place?

No, I wouldn't because it doesn't work that way for me or for a lot of other people. We need the higher (inspiratory) pressure to prevent obstructive events. The exhalation pressure relief provides comfort only.

In my case, I need the lower expiratory pressure to help relieve aerophagia, but I can't set it too far below the inspiratory pressure because then it raises my CA index. But if I lower the inspiratory pressure below my titration pressure it raises my hypopnea and OA indices.