Hypopnea Scoring

This may sound rudimentary but I need a more concrete answer on when you see the desaturations when scoring hypopneas. Should the desat be seen after the drop in amplitude (if yes, what's the reasonable time frame - no more than, e.g., 30 sec before the actual desat?), during, or even after (There are times when there is an obvious drop in amplitude but not, initially, at 30%.)?

From the American Academy of Sleep Medicine:

Score a respiratory event as hypopnea if ALL of the following criteria are met:
a. The peak signal excursions drop by >30% of pre-event baseline using nasal pressure (diagnostic study), PAP derived flow (titration study), or an alternative hypopnea sensor (diagnostic study).
b. The duration of the >30% drop in signal excursion is >10 seconds.
c. There is a >3% oxygen desaturation from pre-event baseline or the event is associated with an arousal.

As stated above, if criteria a and b are met, then a hypopnea is scored if there is at least a ≥3% oxygen desaturation from the pre-event baseline OR the event is associated with an arousal. Thus, the event could be associated with only a ≥3% oxygen desaturation, only an arousal, or both.