I had an overnight in a sleep disorder clinic and then several weeks later another one. I never slept at all during either test because, I guess,  of all the noise and the discomfort. One doctor had me sign a paper indicating that I would not use the cpap treatment he recommended. But another doctor, after reviewing the same information, recommended oxygen at night while sleeping and that has been very successful for about 10 years now. I need the oxgen also for an after noon nap. I am presently 82. I live in a town at 6500 feet altitude. When I travel, I find that below about 2500 feet I sleep very well. Can't sleep on airplane, of course. I have noticed that nearly all discussions of apnea are about the obstructive type. Where can I find timely information about this central apnea? Thank you.