WearyOne wrote:
1. What does 90% mean at the highest pressure when the number of minutes is less than under the 8.8 pressure?
Weary One, you are not reading the labels on the summary pressure numbers very clearly: The posted Encore report says that your
mean pressure was 8.8. The posted graph indicates your 90% pressure is about 9.65 cm.
Both
mean and
90th percentile (90%) are statistical terms. For a detailed explanation of how these numbers are typically computed and what they mean statistically see my blog entry
Average, Median, 95% numbers: A guide to those who don't remember their introductory stats
The
mean pressure = 8.8 simply means that if you multiply each (distinct) pressure setting by the time you were at that pressure and add those numbers together and then divide by the total run time, you get 8.8. In other words, the mean pressure number is nothing more than a weighted average.
The
90th percentile )90%) is a statistical term. When Encore says that your 90% pressure is 9.65, that means for 90% of the time the machine was running your pressure was BELOW or AT 9.65 cm. It also means that for 10% of the night your pressure was ABOVE or AT 9.65cm.
As for the numbers in the table: First, you need to understand that the PR machines increase pressure in .5 increments. And in the table, the *.5 pressures are rounded UP, not down. So any time you spent at 9.5 cm of pressure is part of the 10cm box. If you add the times at pressure numbers together you get:
114 + 55 + 73.5 = 242.5 minutes of therapy time.
And 90% of 242.5 is 218.5 minutes. So to compute the 90% pressure level, we look for the 218.5 minutes at LOWEST pressures. We keep a running total:
Time at 8 cm = 114.0 (So the 90% pressure level must be > 8 cm)
Time at 8 + time at 9 cm = 169.0 (So the 90% pressure level must be > 9 cm)
Time at 8 + time at 9 cm + time at 10 cm = 218.5 (So the 90% pressure level must be <= 10 cm)
The actual 90% pressure level shown in the graph is 9.65. The reason why is pretty simple: When the machine increases the pressure from 8.0 to 8.5 cm, the pressure increases
linearly. In other words, as the pressure is increased, there is a tiny amount of time spent at 8.1, 8.2, 8.3, and 8.4 cm. And when the Encore program analyzes all of the data, the pressure when the running total of time first equals or exceeds 218.5 minutes is about 9.6 or 9.7 cm.
2. What's the the large vibratory snore (112) at the highest pressure on Daily Events per hour? How does this correlate with the sleep therapy flags that has a much lower number (35)? Snores are usually less than 10 on CPAP, but I was on the couch with this one and might have been in some really odd positions!
The large vibratory score at 10cm is computed using the snore data gathered WHEN the pressure was between 9.5 and 10 cm and then the total of the snore data is divided by the time spent with the pressure between 9.5 and 10 cm.
In looking at the the event table data as well as the "time at pressure data", it appears that you started snoring and the machine quickly raised your pressure to the max setting and you continued to snore. The snore total while you were between 9.5 and 10 cm of pressure can be computed as follows:
VSI at 9.5-10 cm = 112.5 "snores"/hour
==> "total snore total at 9.5-10 cm" = 112.7 * (time in hours at 9.5-10 cm)
==> "total snore total at 9.5-10 cm" = 112.7 * (73.5 minutes/60) hours
==> "total snore total at 9.5-10 cm" = 137 or 138 (due to round off error)
Now almost none of your snoring seems to occur at pressures less than 9.5 cm because as soon as you started snoring the machine increased the pressure all the way up to 10 cm. Hence if we divide the "total snore total at at 9.5-10 cm" by the "time the machine was running" we get a rough,
lower bound on the VSI for the whole night. You used the machine for 218.5 minutes, which is 3.64 hours. So the VSI for the whole night must be a bit larger than
137/3.64 = 37.63, which is about what you say your VSI typically runs on the straight CPAP.
3. Why is the average leak so low? On the cpap it's around 40. (Innomed Hybrid)
This one stumps me.
Any thoughts, suggestions, or advice would be welcome!!
If you found the changing pressures of the APAP bothersome, why not simply set the APAP into CPAP mode and use your normal pressure of 8.5cm?
