Total leaks LESS than spec'd intentional leaks?

[phildoc]

Here's a bit of a puzzle .. to me, at least.

First post, brief background -- began CPAP three weeks ago (sleep study showed AHI of 45.1). Machine is PR System One DS460; pressure is 12; mask is Fisher and Paykal Pilairo.

I have been using Sleepyhead (many thanks for the tutorials, Pugsy), and all looks great -- 21 day avg RDI is .96, and after a few rocky opening nights things have been far smoother than I had any right to expect. I am not using a DME (deductible is too high, so it's been cheaper to get gear on my own), and I was very surprised (and very lucky) that my first mask has been so comfortable.

My question -- I know that for a PR machine, Sleepyhead reports two lines -- total leak and their best estimate of unintentional leak. According to F & P, the flow rate for the Pilairo at a pressure of 12 in 34 L/min. Here's what strikes me a odd -- for a number of days, my total leak is well below 34 l/min, and SH reports that average leaks (over 20 days) is 29.49 L/min. How's it possible for the total leak rate (intentional plus unintentional) to be below what Fisher and Paykal claim is the intentional vent rate? My best guess is that F & P's table is more of an estimate than a precise rate...is that so?

I just downloaded EncoreBasic 2.2, and it shows (over that same 20 day period) 0 sec of large leak, and an average AHI of .8, so I am not worried, just curious.

Can't say enough about how helpful this board has been!

[Pugsy]

There's actually a standard deviation plus or minus with any intentional leak graph. It used be in there in tiny print on the paperwork. I haven't looked for a long time to see if they have changed it.
What you are seeing is actually pretty much within an acceptable deviation range.
When I was using my Swift FX nasal pillows almost always the average leak was 5 or 6 below what the chart showed.
So yes, it is fairly common for average total leaks to be slightly less than what the paperwork graphs point and nothing to worry about and just means that for the most part...leaks aren't an issue or the average would be higher.

[phildoc]

Thanks, Pugsy. That was my initial assumption, but it's nice to have it confirmed by someone who knows.

[archangle]

Do you use Flex or ramp? Either of those would slightly lower your average leak rate.

[phildoc]

I do use a 10 minute ramp (starting a 6), and flex (set at 3). Hadn't thought about the impact of those...thanks.