Pugsy wrote:Anyone wondering....in EncoreBasic there is a way to change the default Total Leak report to show only Excess Leak like the S9 reports.
It's not going to be perfectly exact because the machine doesn't know which mask you are using but instead takes sort of a generic reading at the beginning of the night when leaks are most likely not an issue and bases calculations on that guesstimate.
Actually Pugsy I think it's doing some kind of statistical analysis to decide what it thinks is the intentional leak.
And the Resmed machine does it's own guessing. You choose the type of mask and the S9 uses a generic figure for that type of mask. But different masks of the same type do not have exactly the same expected leak curve. However, the differences between the individual mask's expected leaks is (properly) assumed to be statistically insignificant.
If you are using higher pressures it doesn't mean that your baseline is always at zero though...I don't often go into this explanation because of that fact.
People assume that the baseline for excess leak has to be 0.0 L/min and it isn't always the case. Gets them all upset.
I have a friend using 16.5 cm pressure...her baseline when reporting excess leak only is around 20 L/min. It simply won't/can't go below that line and we know the leaks are very well controlled. Her same total leak line is around 55 with her FFM and her pressure.
Asking for clarification: What do you mean when you say her baseline for reporting excess leak is only around 20 L/min? And her total leak line is around 55 L/min?
My guess is that you're saying that her total leak line hovers right around 55 L/min, but that SH shows a constant (excess) leak rate of around 20 L/min that parallels the stable total leak line? Most FFM user guides that I've seen show an expected leak rate of around 50 L/min for a pressure of 16.5: So a stable leak line at 55 L/min would indeed indicate no problems with leaks. But if SH's stats were correctly figuring the (unintentional or excess) leak rate, then she ought to have a leak graph that is hovering right around 0.0 instead of hovering around 20 L/min. Under the CPAP tab of the SH preferences panel, does she have "statistical model" selected for
leak calcs? If she's got that option selected and her leak line is hovering around 20 L/min, she ought to submit a bug report through the SleepyHead webpages at sourceforge.net.
And it's worth pointing out here for others: The user manual for your mask will contain a chart or a graph of the expected (intentional) leak rates for the mask at different presssures. But even here, the numbers are not absolute. The reason? Those published intentional (expected) leak rates are statistical data. They should have +/- margins of error published with them; some masks' user guides do include the +/- margins of error, but others don't include that info. Because of this, the published expected leak rates should be interpreted as "roughly where you should see a mostly flat
total leak line". But the total leak line might be a bit above or the published expected leak rate:
- Pugsy's friend's mask's user guide says she should expect a total leak line somewhere near 50 L/min and her leak line winds up at 55 L/min, which is a bit above the published expected leak rate.
- The Swift FX user manual indicates that at my pressures the expected leak rates should range from 20 L/min (at min EPAP=4) to 29 L/min (at max IPAP=8) and in practice my leaks are usually stable around 15-16 L/min at pressures of 6/4 and 18-20 L/min at pressures of 8/6, which is a bit below the expected leak rate.
But both Pusgy's friend and myself have stable total leak lines that are
near the published expected (intentional) leak rate for our masks and our pressures. So the data indicates for both of us that leaks are well controlled.
So people have to base excess leak on their baseline and not necessarily 0.0. It's hard for people to comprehend sometimes and gets them upset thinking they never have leaks well controlled and that's why I don't go into pushing changing that setting.
Instead I tell people to look at the line...if it is pretty stable it doesn't matter what the numbers say.
Agreed. But typically both Encore and SH should do a pretty good job statistically speaking of picking a decent estimated leak rate for the Excessive Leak (Encore) and Leak (SH) graphs.
For example, on a night where my baseline total is pretty close to 15, SH will start showing small bumps in the Leak graph if my total leak gets up near 18 L/min; but on a night where my baseline tota is pretty close to 19, places where the total leak drops to 18 don't show up as bumps in the Leak graph.
For me I find that subtracting the median total Leak from the median Total Leak gives a very good estimate of my expected leak for the night. But my leaks are well controlled.
And remember...if using auto adjusting pressures that leak line is going to move somewhat as the pressures increase.
Total leak line will DEFINITELY go up as pressure goes up. The Leak line (SH) and Excess Leak line (Encore) may or may not go up; it all depends on the statistics are being done AND how fast and how far the pressure increases. For my small 2cm increases in pressure I often see a rise in the Total Leak line in SH and no rise in the Leak line. In looking at other's data here, sometimes I see rises in both graphs and sometimes the rise is only in the Total Leak graph. It all depends on how fast and how much the pressure increased.
