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→Leaks
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All machines ''other than ResMed'' record and report the '''''Total Leak Rate'''''. Total Leak Rate includes both the ''intentional leak rate'' built into your mask to prevent re-breathing of CO2 AND any ''excessive (bad) leaks''. In other words:
Modern CPAP machines are designed to gracefully cope with a certain amount of excessive leak by blowing additional air into the semi-closed system in order to preserve the desired pressure setting. But even the best of machines cannot accommodate really large amounts of excess leak.
All that said: It's not uncommon for people to simply have a bad night for leaks every now and then. If your leaks are usually decent enough, it can be counter-productive to worry about eliminating the last of the leaks.<br />
A ''perfect Leak/Total Line'' is a leak line with little or no unintentional leaks.
To identify a perfect leak line from Total Leaks requires a bit of knowledge: We need to know the ''expected (intentional) leak rate'' for the mask. Once we know that, a ''perfect Total Leak line'' would be a flat or "fuzzy flat" line that is within a few L/min of the expected leak rate for the mask at the given pressure.
The ''expected rate'' depends on both the mask and the pressure. The owner's manual for your mask should have a table and/or graph that tells you what your mask's expected (intentional) leak. The chart below shows the design flow rate is at different pressures for a variety of pressures. Here's the expected leak rate information from page 8 of the user guide for the ''ResMed Swift FX nasal pillows masks and mask''types:
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[[File:SwiftFX-chart_zps1a3bc596Resmed Pressure vs Flow.jpgpng]]
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For the Swift FX mask, We interpret this chart as follows:
These numbers are not precise-- they typically include a +/- margin of error of about 5 L/min. But in an ideal world, you want your Total Leak graph to be pretty close to your expected leak rate.
We'd all like a perfect leak line every night. But for most of us, that's not going to happen. Moreover, the battle to eliminate all excess leaks may cause more problems than it fixes. So when are leak lines "good enough" to not worry about it?
But it's also important to understand that if the 90% or 95% Leak/Total Leak Rate is just barely above the definition for Large Leak for your machine, your leaks might still be "decent enough". In this case you really do need to consider just how much time you spent in Large Leak territory: It's one thing if you are spending 15-20% of the night barely above the Large Leak line; it's another thing if you're spending 40-45% of the night AT or ABOVE the large leak line. And yet, the 90% (and 95%) Leak/Total Leak numbers can look the same for both situations.<br />
As with many other things concerning CPAP therapy, trending data in the Leak/Total Leak line is also important. If you're trying out a new mask and you're still working out how to fit the mask, you may have one or more nights of really bad Large Leaks. If your mask cushion is starting to wear out, the first sign might be a higher than normal leak line. If you wind up with a bad cold or the flu and you're seriously congested, you might be prone to doing more mouth breathing than normal and your leaks may be (much) higher than typical. So it's important to not over-react to one (or a few) bad nights with respect to leaks, particularly if there's an obvious explanation.
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A lot of things can cause leaks of all sizes: Fiddling with the mask, jostling the mask to scratch your nose, jostling the mask while turning over in bed, mouth breathing, and facial relaxation (facial sagging) in deep sleep are all capable of causing both small and large leaks. Worn out mask cushions, incorrectly sized masks, overtightened mask straps, and masks that are incorrectly reassembled can also cause leaks. Another potential cause of leaks are pressure increases when using a CPAP in auto mode. Fitting a mask at low pressure tends to be easier than fitting a mask at higher pressures. And if you fit your mask at relatively low pressure, as the pressure increases, the pressure increase itself may cause the mask to lose its seal, and the result is an excessive leak.
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There are three types of leaks:
And some people find themselves in the middle: Leaks sometimes seem to cause problems. Or perhaps certain types of leaks cause problems, but they can sleep through other types of leaks. If you find yourself in this situation, use some common sense when evaluating your leaks. How big of a problem is it really? And is the cure more of a problem than the leak? Dry mouth may or may not mean that you are seriously impacting your therapy with mouth breathing. And if your mouth leaks seldom reach Official Large Leak territory, you have to weigh the potential discomfort of wearing a chinstrap, taping your mouth, or using a FFM against the potential problems caused by the non-Official Large Leak mouth leaks. This is a personal call and has to be made on an individual level. Some people will be more comfortable having less leaks and more stuff on their face; others will be more comfortable sleeping with a few more leaks and (a lot) less stuff on their face. As long as your leaks are not staying in Official Large Leak territory for excessive periods of time night after night, the best decision is the one that gives allows you to sleep most soundly with the fewest wakes. <br />
We've looked at how each manufacturer defines an Official Large Leak, we examined leak lines in order to figure out how to tell if leaks are a significant issue, and we've looked at some causes for leaks. But we haven't actually looked at why Large Leaks cause problems for our CPAP machines and how those problems may affect our therapy.
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