(05-03-2016 05:57 AM)mscottc Wrote: If free flowing air isn't a large leak, what is?
If the free flowing air is coming from the exhaust vents of the mask, that's the intentional leak
built into the mask to prevent you from rebreathing the CO2 you exhale. The intentional leak rate for a mask depends on the pressure you use; the higher the pressure, the larger the intentional leak rate is. The mask's design also affects its intentional leak rate. The user guide that came with your mask should have a chart that indicates what the intentional leak rate for your mask is at various pressures.
Quote:What comprises a "Large Leak?"
A "Large Leak" is a leak that is well above the intentional leak rate for the mask. For example, if your mask's intentional leak rate is 30 L/min at your pressure, but the machine is detecting a total leak rate of 65 L/min, then the unintentional leak rate is 35L/min since 65-30 = 35. Whether an unintentional leak rate of 35 L/min is an official Large Leak depends on the particular CPAP machine that you are using.
Some manufacturers are very clear about what constitutes a Large Leak. For example, Resmed defines any excess leak over 24 L/min as a Large Leak. (And the Resmed machines record only
the excess leakage.) PR, the maker of Resprionics machines, is more vague about how big a leak needs to be before it will get flagged as an official Large Leak.
I've not seen enough DreamStation data to know roughly where the line is on those machines. On the slightly older System One Series 60 PAPs, however, Large Leaks tend to be scored only when the total leak
is up around 60-70 L/min if you are using pressures of 10 or more. For people with lower pressures, official Large Leaks can be scored when the total leak rate
gets up around 50-60 L/min.
Quote:I've been using a Respironics Dream Machine with an Amira View mask for the last two weeks now, and every night I seem to have to remove the mask,to reseat it to stop a leak or disconnect the hose forgetting to turn off the flow. In 14 nights of usage, I have not shown one "Large Leak."
The leak rate is sampled several times a minute as I recall, but it is not continuously monitored. If you briefly reset the mask or briefly remove it, it is possible for the "Large Leak" to be so transient that it is not picked up in the sampling process.
When you disconnect the hose or take the mask without turning the machine off, the machine quickly determines that there is not a living, breathing human being at the other end of the system. That time is counted towards "Blower Hours" (the CPAP equivalent of a car's odometer), but it does not count towards "Therapy" Hours, which only count the time that breathing is detected. If the machine has determined that there is not a real, live person at the other end of the system, it does not score the (very large) leak as a Large Leak simply because it only worries about scoring Large Leaks during Therapy Hours.
If you were to look at your data in Encore or SleepyHead, the time that the blower is on, but the machine cannot detect a breathing pattern is flagged with a big, ugly black bar that is coded BND, for "Breathing Not Detected".