Please note that the 90% AutoCPAP (Pressure) reported on the Respironics EncorePro (EP) Sleep Therapy Daily Details page is weighted by minutes at Pressure. To determine the 90th centile for pressure, the "minutes at Pressure" values are accumulated starting with the lowest pressure in the range until a pressure value is reached where the accumulated "minutes at Pressure" when divided by the total minutes at all reported pressures is 90% or greater. The data used by EP for this determination is shown in the Daily Events Per Hour table at the bottom of the Sleep Therapy Daily Details page.Let's take two different sets of numbers. The first set is:
1, 2, 2, 2, 2, 16, 16, 16, 16, 17
Let's assume (unreallistically) that this is pressures. The total of these numbers is 90. The average (mean) value is 9. The 90th percentile is about 16. In other words, though the average is 9, to address most of the events, you need a pressure of 16.
A graphical representation of this 90% AutoCPAP determination is shown on the EP Summary of Daily Details page along with its data table (used to determine the 90th centile value).
Since I run my AutoCPAP with the same min & max pressure (of 8 cmH2O), I do not have the data to fully investigate the 7-day avg and 30-day avg LCD displayed values for 90% Pressure since, with a constant pressure of 8 cmH2O, my LCD always shows the 7 & 30-day avg 90% Pressure as 8.0 cmH2O.
However, based on circumstantial evidence including data residing in one of the EP SQL tables, I believe that the LCD displayed 90% Pressure numbers are weighted by minutes at Pressure and will, therefore, match those determined by EP.
In the quoted example above, if the minutes at pressure for pressure values of 1 & 2 total 90 minutes or more and the total minutes at all pressures (including the pressure values of 16 & 17) is 100 minutes, then the 90% AutoCPAP Pressure will be 2. Please note that if each value in the quoted set of numbers has the same duration, then the 90% AutoCPAP Pressure will be 16 (not about 16 but 16) since the last 16 value will correspond to 90% of the "minutes at Pressure" as it is 9th in a series of 10 values.