How Exactly Does REMStar Compensate for Mask Leak?

littlefeat · Post by **littlefeat** » Fri Apr 22, 2005 4:27 pm

Sorry If I've missed it on prior threads, but does anyone know PRECISELY what the REMStar machines do to compensate for mask leaks, or for switching masks that have different exhaust leak rates, to ensure that delivered pressure to the airway is as set on the machine?

-SWS · Post by **-SWS** » Fri Apr 22, 2005 10:12 pm

A fixed pressure CPAP machine would employ a basic pressure feedback loop. If a leak occurred, that pressure feedback loop would cause the blower rotations to increase until the leak had been compensated for. However, a massive leak can outstrip any CPAP unit's leak compensation capabilities: a blower can only spin so much to compensate.

An AutoPAP by contrast is much more concerned with flow measurement since the AutoPAP relies on flow based signals to trigger. The AutoPAP bases its leak calculations on the fact that inspiratory airflow should come extremely close to equaling expiratory airflow.

Mikesus · Post by **Mikesus** » Sat Apr 23, 2005 5:31 am

Here is a visual from Respironics that will give you an idea of how it determines leak

It will increase blower speed until the peaks are at the same level as prior to the leak. (the cycle shown is an simplified view of your breathing cycle)

littlefeat · Post by **littlefeat** » Sat Apr 23, 2005 7:07 am

Thanks, SWS and Mikesus.

The literature on the patent for the REMStar Auto with C-Flex indicates that, whether in CPAP or APAP mode, the leak compensation approach actually is a drop in machine pressure hoping that this will stir the patient to move and reseal the mask or allow the mask to reseat itself, so it doesn't seem to involve a pressure increase. My understanding, until reading this today, had been like yours. I tried to get info from the cpap.com help desk, since I bought my Activa there, but they werent' sure about this either.

My basic question is this: I am switching to the Activa from the HC405, and the Activa has a higher exhaust leak rate than the HC405. If I leave my REMStar Auto (presently in CFlex mode) at the same pressure of 12, which I used with the HC405, am I getting the same airway pressure, and is the machine smart enough to read airway/system pressure and adjust accordingly? At the same pressure setting of 12 on the machine, my AHI seems higher than with the HC405, and the leak is around 33 rather than around 27. Should I have to increase the machine setting somewhat to compensate for the higher exhaust leak rate of the Activa, or does the machine automatically compensate for this to ensure the same delivered pressure?

john67 · Post by **john67** » Sat Apr 23, 2005 8:10 am

What happens when the leak in the mask increases the CPAP blower increases speed to maintain pressure. You need more air flow or volume from the CPAP blower to maintain pressure with a larger leak in the mask. Pressure and volume are not quite the same. The CPAP is sometimes called a blower or flow generator because you need lots of air volume not pressure. An air compressor on the other hand is designed to generate high air pressure at low volume and that why there is a large tank in car tire shops with air compressors. The portable air compressor that you can buy for your care tires will generate high pressure but the CPAP can move large volume of air far better than a compressor. Keep in mind that the pressure from the CPAP is measured in cm of water which normally does not quite make ½ PSI!

littlefeat · Post by **littlefeat** » Sat Apr 23, 2005 9:22 am

What about a different, but consistent, exhaust leak level from changing masks? For example, the machine is set at 12 cm for two nights, one night exhaust leak (steady all night, not a seal leak) is at 27 with one mask, and the second night exhaust leak is at 33 with another mask. Is the machine delivering the same airway splint pressure both nights, with the two different masks?

john67 · Post by **john67** » Sat Apr 23, 2005 10:08 am

littlefeat wrote:What about a different, but consistent, exhaust leak level from changing masks? For example, the machine is set at 12 cm for two nights, one night exhaust leak (steady all night, not a seal leak) is at 27 with one mask, and the second night exhaust leak is at 33 with another mask. Is the machine delivering the same airway splint pressure both nights, with the two different masks?

The machine will maintain the same pressure but with different flow rates up to a point that reaches the machine limit.

-SWS · Post by **-SWS** » Sat Apr 23, 2005 11:28 am

littlefeat wrote:The literature on the patent for the REMStar Auto with C-Flex indicates that, whether in CPAP or APAP mode, the leak compensation approach actually is a drop in machine pressure hoping that this will stir the patient...

I was unaware of that "wake the patient with a pressure drop to fix the leak" strategy. My first impression was: what a bizarre strategy! The REMstar does have audible leak alarm capability, and that should be used to wake the patient if/when the patient allows that feature to be turned on. It sounds as if one way or another the patient is bound to receive an alarm if the leak is massive enough. I'll have to read the description in detail, but it sounds as if this particular pressure drop strategy is not the primary leak compensation method---rather it would have to occur only during massive leaks as a last resort method. Otherwise cortical arousals from pressure-drops could easily outstrip cortical arousals from unaddressed obstructive sleep events---especially with low AHI patients.

John67 · Post by **John67** » Sat Apr 23, 2005 1:34 pm

-SWS wrote:
littlefeat wrote:The literature on the patent for the REMStar Auto with C-Flex indicates that, whether in CPAP or APAP mode, the leak compensation approach actually is a drop in machine pressure hoping that this will stir the patient...
AHI patients.

Sounds like saying it does not have a leak compensation circuit! Without a compensation circuit of course the pressure will drop!