Just to clarify and add a little to what was already said,
a RERA (respiratory effort related arousal) actually does not include an apnea or hypopnea, it only includes the 'wannabes'...a RERA is when you have a flattening of the nasal pressure waveform, or increasing respiratory effort that leads to an arousal (an 'arousal' is a change in your EEG waveform and possibly a change in muscle tone/tension). basically when a doc is looking at RERAs they're looking at possible respiratory problems that can't be defined as a clear cut apnea or hypopnea (for example, no desaturation in your blood O2) but still are causing interruption of your sleep (arousals). like UARS which was already mentioned. when they mention the 'index' they're simply referring to the averaged number of RERAs you experienced per hour during your study.
a baseline oxygen saturation is typically a 'normal' oxygen saturation, its kindof used like a yardstick to measure O2 variations against.
the numbers at the end of your post mean this:
your average O2 saturations while you were in REM (combined) was 96%, your average O2 saturations while you were in NREM (non-REM, also combined) was also 96% both of these are good.
and lastly, that actually should look like a table but in forums its hard to post those. it says that while you were in REM, your oxygen saturation (SaO2) was below 90% for 0.1 minutes, with zero minutes below 80%(and subsequently 70% and 60%)...and while you were in NREM (non-REM), your O2 levels were below 90% for 0.3 minutes, with zero minutes below 80% (also 70%,60%) these numbers are for the entire course of your study, so if this info is from your CPAP night study, then it includes ALL the pressures they tried, both the successful and less-successful pressures. but either way these are good numbers.
central apnea can indeed be a sign of other medical problems, but aren't always, it would be worth talking to the doc about when you next meet with them, or give them a call or something. but if the tech told you that you were controlled with NO respiratory events at a pressure of 9, to me that sounds pretty good. a good portion of the diagnosed population tend to end up with a pressure of between 8-12, so your results sound good and normal to me.