90%

Can someone explain what the 90% means when I'm in A-Pap mode? I'm guessing it means the pressure I was at 90% of the night, but then why is the AVG pressure different? Wouldn't they be about the same? My Avg is 9.19 and my 90% is 10.5. Thanks!

The math is different so both numbers while they are close are not the same. You have the concept right.

It is just a number.
90% of the time your were at OR below that pressure....don't forget the or below part.

Overall average might be a better one to keep an eye on on a daily basis. That 90% number can be falsely elevated sometimes.

Or if you want to look at the 90% number...look long term and not nightly.

My long term (over months) 90% pressure on APAP was barely 12 cm but some nights I saw 17 cm 90% pressure...some stubborn events sometimes and sometimes the machine trying to fix a leak with more pressure.

Resister wrote:Can someone explain what the 90% means when I'm in A-Pap mode? I'm guessing it means the pressure I was at 90% of the night, but then why is the AVG pressure different? Wouldn't they be about the same? My Avg is 9.19 and my 90% is 10.5. Thanks!

The 90% pressure number represents the 90th percentile of the pressure levels for the night. Since your 90% pressure is 10.5, that means that your pressure was AT or BELOW 10.5 cm for 90% of the time the machine was running. It also means that your pressure was AT or ABOVE 10.5 for 10% of the time the machine was running.

In SleepyHead, the default "average" is a so-called "weighted average". If I recall correctly you can understand how the weighted average is calculated by thinking of it like this:

Multiply each pressure level by the time spent at that pressure. And then divide by the total time. As a very simplified example where I'm ignoring intermediate pressure setting entirely. Let's suppose you are running in APAP mode in a range of 7--12 cm and that you slept for 7.5 hours. And lets suppose that the time you spend at each pressure setting is as follows:

• 7cm: 1 hour
• 8cm: 2.5 hours
• 9cm: 2 hours
• 10cm: 1.5 hours
• 11cm: 0.5 hours
• 12cm: 0 hours

Your weighted average would be calculated as follows:

(7*1 + 8*2.5 + 9*2 + 10*1.5 + 11*0.5 + 12*0)/(1+2.5+2+1.5+0.5+0) = 8.73

Note that 90% of 7.5 hours is 6.75 hours. If you add up the times spent at 7, 8, and 9cm of pressure, that's still less than 6.85. If you add up the times spent at 7, 8, 9, and 10cm of pressure, that's over 6.85. Hence, in this very simplified version of things, your 90% pressure setting would be 10cm.

And just to muddle the waters further, if you change your preferences in SH to use the MEDIAN for "middle calculuations", the MEDIAN pressure number is the number where you spent 50% of the night AT or BELOW that pressure and you spent 50% of the night AT or ABOVE that pressure. In the above example, 50% of 7.5 is 3.75 hours. Given the data as presented, the MEDIAN pressure would be 9cm since for 3.75 hours of the data your pressure was AT or BELOW 9cm and for 3.75 hours, your pressure was AT or ABOVE 9cm.

As for your real data: Your 90% pressure level is quite a bit higher than your average pressure because relatively speaking you spent more time at LOWER pressures in your range that you did at the higher pressures in your range. In other words, you're not using pressures above 10cm any where near as often as you
as you are using pressures AT or BELOW your average pressure of 9.19cm. My guess is that if you look at the pressure curve, you'll see that it stays below 9 or 9.5 cm for much of the night---probably close to or even more than 50% of the night. And that it's above 10cm for much less time than it's AT or BELOW 9cm.

In general: If your AVERAGE and 90% readings are VERY CLOSE to each other, that means that you are OFTEN using pressures AT or ABOVE your 90% level. If your AVERAGE and 90% readings are far apart, that means that you are staying at relatively low pressures for significant amounts of time AND you are also having some measurable amounts of time AT or ABOVE your 90% level. If your AVERAGE pressure level, your 90% pressure level, and your MAX pressure level are all very close to each other, that means you're hitting the maximum pressure pretty often during the night. If your AVERAGE pressure level is quite a bit lower than the 90% pressure level and your 90% pressure level is about what your Max level is, that means you are probably only hitting that max level about 10% of the time.

Today's stats lesson is brought to you by Robysue, the friendly math prof

Y'all are the greatest! Thanks for helping me understand.