how fast does cpap machine respond to mask leaks-instantly?

My DME told me that mask leaks don't matter if they are under the Resmed maximum!--25??, because Resmed will compensate up to its maximum. OK as long as the leak is not throwing air into your eyes and waking you up, I said. But I always wondered what happens when you have a mask leak. For that matter how does the machine regulation of the pressure work???

Questions:

When you set the pressure on the machine in cm's ---is this the pressure Resmed expects to be at the mask (by algorithm?) or the pressure at the machine and not necessarily the pressure at the mask?

Supposing you had a small mask leak around the mouth corner on just one breath exhalation or inhalation--Is ResMed's response "instantly" and automatically to create more pressure for just that period of time, to maintain the pressure that the machine was set at? or is there a delay? How does this show up in Oscar when looking at the pressure graph and the mask pressure graph?

Secondly, what happens if you change locations from the seaside to the mountains? or the seaside to the top floor of a condo on the hill? If you have the machine set for 10cm's, does the machine just give you 10cm's greater than the current atmospheric pressure in the room, wherever it is? during the middle of a low pressure storm? If the atmospheric pressure changes just before or after a storm, does your CPAP instantly change too??

If you compare your Pressure trace to your Leak Rate trace in OSCAR you will not find an obvious and discernible correlation between the two. This suggests that the pressure is maintained close to "instantly", or at least as close as it needs to be.

Modern day CPAPs compensate for pressure variation and altitudes changes up to about 8000 feet.

The response time is in your manual. For Resmed… I think it is 8 or 9 seconds. After breathing interruptions of 8 or 9 seconds, the machine figures an apnea event is occurring. In the autoset mode, the machine will increase it's pressure to treat the apnea. Once treated, the machine's pressure will back down and wait for another apnea event. The delay is for coughs, sneezes, etc... I've notice when I flip over, I hold my breath. I wouldn't want pressure gyrations for those times.

Sheriff

tyrinryan wrote: ↑

Mon Apr 20, 2020 8:34 am

My DME told me that mask leaks don't matter if they are under the Resmed maximum!--25??, because Resmed will compensate up to its maximum. OK as long as the leak is not throwing air into your eyes and waking you up, I said.

I can't believe it, a DME told the *truth* about something???*boggle* though, it is 24lpm

tyrinryan wrote: ↑

Mon Apr 20, 2020 8:34 am

But I always wondered what happens when you have a mask leak. For that matter how does the machine regulation of the pressure work???

The machine measures the pressure many times per second, (I forget how many exactly, something between 50 and 125 per second) and makes adjustments to the speed of the motor to maintain the called for pressure at that instant. In addition to leaks, it also compensates for the pressure drop as you inhale, speeding up, and the pressure increase as you exhale by slowing down. Plus it's changing it's target pressure constantly if you're using EPR.

tyrinryan wrote: ↑

Mon Apr 20, 2020 8:34 am

Questions:

When you set the pressure on the machine in cm's ---is this the pressure Resmed expects to be at the mask (by algorithm?) or the pressure at the machine and not necessarily the pressure at the mask?

It's the pressure the machine creates at the mask, compensating for pressure drops all along the circuit caused by the humidifier, tube diameter and length, presence or absence of a AB filter in the tube, and even the type of mask resistances. The algorithm is very complicated, but the computer in the machine is quite smart.

tyrinryan wrote: ↑

Mon Apr 20, 2020 8:34 am

Supposing you had a small mask leak around the mouth corner on just one breath exhalation or inhalation--Is ResMed's response "instantly" and automatically to create more pressure for just that period of time, to maintain the pressure that the machine was set at? or is there a delay? How does this show up in Oscar when looking at the pressure graph and the mask pressure graph?

The "pressure' graph is the commanded pressure, what should happen. The "mask pressure" is the measured pressure, compensated for those circuit pressure drops mentioned above. If your leaks are so bad that the machine can't compensate for it, you'll see the pressure drop show up on the mask pressure chart.

The 24lpm level is where the machine can comfortably still differentiate between obstructive and central events, not when it can't compensate for pressure. Depending on your set pressure, the machine can maintain pressure well over 100lpm of leak, but it won't be able to tell what's going on.

tyrinryan wrote: ↑

Mon Apr 20, 2020 8:34 am

Secondly, what happens if you change locations from the seaside to the mountains? or the seaside to the top floor of a condo on the hill? If you have the machine set for 10cm's, does the machine just give you 10cm's greater than the current atmospheric pressure in the room, wherever it is? during the middle of a low pressure storm? If the atmospheric pressure changes just before or after a storm, does your CPAP instantly change too??

Well, pressure is measured against ambient, so, none of that matters.

Nothing happens "instantly", but it does happen faster than you can discern.

Sheriff Buford wrote: ↑

Tue Apr 21, 2020 8:09 am

The response time is in your manual. For Resmed… I think it is 8 or 9 seconds. After breathing interruptions of 8 or 9 seconds, the machine figures an apnea event is occurring. In the autoset mode, the machine will increase it's pressure to treat the apnea. Once treated, the machine's pressure will back down and wait for another apnea event. The delay is for coughs, sneezes, etc... I've notice when I flip over, I hold my breath. I wouldn't want pressure gyrations for those times.

Sheriff

Apnea's, have to be 10 seconds or longer, and it only increases pressure in response to obstructive apnea's (and hypopneas, snores and flow limitations).

After breathing normalizes, then it slowly starts dropping pressure back to the set minimum,which is why getting the min pressure high enough is important for proper treatment.

Dog Slobber wrote: ↑

Mon Apr 20, 2020 8:44 am

. . . Modern day CPAPs compensate for pressure variation and altitudes changes up to about 8000 feet.

And we have heard of cpaps being successfully used at even higher altitude.