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When CPAP machines detect that the airflow has stopped for a few seconds, they send a series of little air puffs to determine whether the airway is still open (non-obstructive apnea) or blocked (obstructive apnea). The puffs are gentle enough that they don't wake you up and don't force the airway open.

If you're talking full-blown sleep study with all the sensors, then it's pretty easy. If you're attempting to breathe but no air goes in: it's obstructive. If you're not attempting to breathe, it's central. You can detect whether or not someone is trying to breathe by looking at the chest strap reading.

The cause of central apneas isn't always clear, but at high CPAP pressures it can be caused by CPAP, because it can end up blowing off CO2, and breathing is done primarily in response to an increase in CO2.

if you suspect central sleep apnea, you need to work with a specialist that has done research in central sleep apnea. Its a poorly understood condition. But from my understanding treatment is different