Hi again lv3101,
Quote:How did you calculate the margin of error of your machines? Is there any standard xPAP test protocol which would validate xPAP performance?
I don't think there's any standard at all. Other than trying out a completely different data-reporting CPAP machine to see if there's a huge discrepancy.
With regard to the firmware version changes, those changes could be for any reason, not simply an adjustment in the AHI calculations, although it's possible that's what they've corrected. They keep the reasons for the version changes close to their vest, that's for sure, so we really have no clue whether a new firmware version is actually something that vastly improves our machines or not.
Thus far, there's no way for end-users to upgrade the firmware version for any CPAP machine that I know of, other than sending it into an authorized repair facility or to simply purchase a new machine. They don't make the firmware easily accessible or upgradable, because that would make it that much easier for other competitors to reverse-engineer their proprietary algorithms and code that makes their machines unique, thus eroding any competitive advantage they have in the CPAP marketplace.
Regarding your CPAP vs. Lab AHI issues... just something to think about, but it's possible that there was some type of error with the lab equipment or the way in which they conducted the test - not likely, but possible.
If you have major concerns about this, I would see if you could borrow a completely different Bi-level machine (different brand) from someone (perhaps from a local DME who has a used data-capable bi-level sitting around) and set it as much as possible to the same settings as your existing machine, and see what it reports as your AHI. Not sure this is possible, but it might provide useful insight. Tell them that if it reports the AHI correctly, you may be ordering a new machine from them.
To be honest with you, this discrepancy just sounds way out of the ordinary. Yes, CPAP manufacturers might
have a vested interest in under-reporting AHI to make their machines look more effective; these machines are controlled by government regulation, so if there were such an obvious problem with the veracity of the reported AHI, I would think that the manufacturers would suffer the wrath of the regulators for falsely reporting data on their machines.
We have had folks here (with two CPAPs made by two different manufacturers) use both machines with the same settings, and the while their reported AHI levels do have a small difference, usually it's more like 1-2 points for AHI, and that's about it.
The machine's reported AHI is not that important anyway as far as pure accuracy is concerned. Sure, it should be calibrated to as close as possible to real AHI, however the data we all get from our CPAP machines should be used for trend analysis only. So, the 1-2 point AHI variance between different machines should not matter for our purposes as patients - we simply need it to accurately record the differences in AHI from previous nights.
The truth is that there is always going to be some differences in AHI, even between labs using the exact same equipment. It's not like measuring a weight or distance, where there is only one variable and pre-agreed upon, unchangeable fixed numbers. AHI measurements are much more subjective, considering there is no standard on what is considered an obstructive or central event, exactly, or how severe that event must be before being recorded as an actual event with regard to the nightly AHI reporting.
But the AHI differences you report seem vastly different from normally acceptable variance in calibration. If you truly think your machine is messed up with regard to how accurately it's reporting AHI, I'd seriously consider getting another machine, since you may not be getting the most effective treatment. But I don't think this issue is common - you just may have a defective machine.