I have a sleep apnea exam coming up, what can I expect

I have a VA exam coming up for my sleep apnea claim. It’s only 45 minutes long so obviously they aren’t going to actually

test me for sleep apnea, and anyway I’ve already been diagnosed with sleep apnea and have a CPAP machine. So what

are they looking to do here? I also have a rating already for PTSD, should I mention that as well? as a secondary diagnosis?

Any help appreciated. Thanks.