Answer
: Normal Spo2 is 95-100%.
That depends on the individual. That being said a healthy, non smoker can be around 98% give or take. If you have a cold or bronchitis then your lung efficiency will be down, resulting in a lower SPO2. During REM your body slows down your heart rate and your SPO2 goes down. This is normal. As far as determining where and when you have REM through out the night it can be difficult if not impossible using only your SPO2 reading and your CPAP. Normal sleep goes as follows Stage 1-2-3-4-3-2-REM. The AASM has recently done away with stage 4 and coupled it with stage 3 so it looks more like 1-2-3-2-REM. A normal sleep cycle is about 120min. So without and EEG to confirm, a lower SPO2 and a lower heart rate coupled with the ability to remember a dream might, maybe allow you to start guessing when you had REM. Also if you awaken form a dream state and have the ability to go back to sleep after awakening sometimes you'll drop back into REM almost right away (REM rebound). Really the only definitive way would be to have and EEG or someone to look or video tape your eyes at night with a timestamp on the tape to know when REM occurred. That being said there is also tonic/non-phasic and phasic REM. Phasic REM is "normal" REM ie. rapid eye movement, tonic or non-phasic REM is a REM state without eye movements. So really the only 100% definitive way of knowing when REM occur is with and EEG. That being said, if you remember you dreams you had REM sleep at some point during the night. Sorry that kinda got a little long winded and convoluted towards the end.
