Median Leak = 0 ???

apnea13 · Post by **apnea13** » Tue Oct 02, 2007 11:05 am

I have a number instances in which ResScan indicates a Median leak rate of zero (0). The 95th Percentile leak rate in these instances varies from 4.8 to 33.6 L/min with Maximum leak rates varying from 16.8 to 74.4 L/min.

The foregoing appears to defy the definition of median which represents the middle value, not average, within a range of data.

Any ideas?

Slinky · Post by **Slinky** » Tue Oct 02, 2007 11:16 am

Bear in mind that the Resmeds have "pre-deducted" the "allowed" leak rate for their Mask Selections at your pressure. Maybe that has something to do w/the apparent discrepancy??

Out of idle curiosity I'd call Resmed and ask them. If the person you talk to doesn't know the answer they are pretty good at putting you thru to their engineering department.

Ooops. On second thought: they don't support patients who have their software. And the LCD screen wouldn't give you the three leak rates ....

On the other hand ..... you could have gotten those figures from a downloaded report your DME supplier or sleep doc gave you, right? That might get you the answer from Resmed. Like, goshes, is my machine working right, I just noticed this on my report from my doctor (DME).

(Or maybe its that "new math"? Or the US uses a different math than the rest of the world? Or maybe a ghostie has entered your Resmed and is playing games w/you?)

Guest · Post by **Guest** » Tue Oct 02, 2007 4:24 pm

Slinky,
Your idea to check with ResMed is more than prudent. However, I'm afraid I'll "lose it" if I experience the same idiocy as I have on a previous occasion.

I've got another idea. More later, I hope.

I expect what you call the allowed leak rate for a given mask is simply that flow rate venting through a "fitted" mask for a given machine pressure setting. I think it is that ideal flow rate from which one is to draw breaths. Having expressed my thoughts, I've no idea of their significance even if correct.

Slinky · Post by **Slinky** » Tue Oct 02, 2007 5:46 pm

Just that Respironics' reported leak rates include both the "vented flow rate" AND the actual leak rate. Resmeds have subtracted the "vented flow rate" from the total leak rate for their reports.

RiverDave · Post by **RiverDave** » Tue Oct 02, 2007 8:10 pm

Apnea13,

Slinky is right. With the mask correction applied to the flow rate from the machine, it is very possible to have a median value of zero. Basically what it means (to me, anyway) is that you have an excellent mask seal at least half the time.

The ResMed machines seem to record a data point every minute. If, for example, you sleep 300 minutes and for 151 of those minutes, your leak rate is zero, the median for the night will be zero. the 95th percentile reading would be the 15th highest reading the machine recorded that night.

Good Luck,

apnea13 · Post by **apnea13** » Wed Oct 03, 2007 7:18 pm

Very nicely explained, RiverDave. Thank you and Slinky for your generous participation.