(10-24-2013, 02:50 PM)dbrew4 Wrote: Ok...loaded the SH program and the data from my card. I only have 8 days worth because I just stared using my S9. I guess I should start with one or two items in the program. Well here goes with the questions (with plenty more to follow). I'm viewing the stats page for
AHI (?) Most Recent 0.40....Last 7 Days 1.09
Average Leaks...Most Recent 2.82...Last 7 Days 4.52
95% Leaks (?) Most Recent 15.60...Last 7 Days 15.60
The Pressure and Hours per Night is self explanatory
The Stats page give summary information only. Nothing wrong with that, but it's important to understand that these numbers are summary numbers---averages figured over several days (to weeks or months) of data. Summary data is good for detecting long term trends.
AHI stands for the Apnea Hypopnea Index
. This is the basic statistic that measures the efficacy of your therapy. Short story: You want this number to stay under 5.0.
Long story: An apnea
is when you stop breathing for at least 10 seconds. In other words, the machine detects no air going into or out of your lungs for at least 10 seconds. A hypopnea
is when the rate of airflow going into/out of your lungs drops dramatically for at least 10 seconds---your airway is partially collapsed and not enough air is getting through the airway. To compute the AHI, you count up the total number of apneas and hypopneas scored for the entire time the machine is running and you divide that number by the time the machine was running. So, if there were 5 apneas and 6 hypopneas scored and you used the machine for 7.3 hours, the overnight AHI would be computed as:
(5 + 6)/7.3 = 13/7.3 = 1.78
Hence, the AHI is the average number of apneas/hypopneas that occur during one hour of machine use
(or "sleep" since we assume that we're asleep when we're using the machine.) The seven day (and higher) AHI numbers are figured on the data for the entire period. So for the seven day AHI is computed by dividing the number of apneas/hyponeas recorded in the last seven nights by the total time the machine has been used in the last seven nights.
Average leak rate is a weighted
average. For each recorded leak rate, you multiply the time at that leak rate and add everything together and then divide the sum by the total time the machine was running. If you are using a Resmed machine you want this number to be well under 24 L/min (or 0.4 L/sec if you're using an S8 or earlier machine.) And the closer to 0.0 the better off you are. If you are using any machine OTHER than a Resmed machine, you need to know what the expected leak rate for your mask is at your pressure setting since ALL machines other than Resmed machines report total leaks
instead of excess leaks
The 95 percentile (95%)
is a statistical term. In a data set, the 95% value
is the data point at which 95% of the data lies AT or BELOW that value and 5% of the data lies AT or ABOVE that value. To make this statistical idea a bit clearer, a basic example may help: Consider the following list of 100 numbers:
8.4, 8.4, 8.4, 8.4, 8.4, 8.4, 8.4, 8.4, 8.4, 8.4, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 10, 10, 10, 10, 10, 10.1, 10.1, 10.1, 10.1, 10.1
, 10.1, 10.1, 10.1, 15.3, 15.3
The RED 10.1 is the 95th number on the list of 100 numbers. Hence 95% of the numbers on the list are BELOW or EQUAL to 10.1. And that makes 10.1 the 95% of this data set. Also note that there are 5 numbers (5% of the data) that come after that RED 10.1. That's the 5% of the data that is AT or ABOVE the 95% value for the set.
Now to get back to the meaning of the 95% leak numbers. When SleepyHead (or ResScan or the S9's LCD) says that your 95% leak rate is 15.6 L/min, that means for 95% of the night your leak rate was AT or BELOW 15.6 L/min. And for 5% of the night your leak rate was AT or ABOVE 15.6 L/min. In other words, the 15.6 L/min number plays the same role relative to the leak rate figures, that the RED 10.1 plays in the list of 100 numbers earlier in the post.
Again: If you are using a RESMED machine, then ideally you want those 95% leak rate numbers to stay under 24 L/min (or 0.4 L/sec). And the closer to 0.0, the better off you are. If you are using ANY machine OTHER than a Resmed machine, you need to know what the expected or intentional leak rate of your mask at your pressure setting is in order to evaluate the meaning of your 95% leak rate numbers.
A final note about leak numbers
We are human beings and for most of us, an absolute perfect leak line (a leak rate of 0.0 on a Resmed machine all night long night after night) is just not going to happen. But we also don't want to leak like a sieve all night long either. When dealing with leaks we have to be reasonable: There's a point of diminishing returns---once the leaks are well under the border of Large leak territory and they are no longer waking you up and bothering your sleep, they're not worth worrying about.