A minority of people develop central sleep apneas during polysomnography with continuous positive airway pressure titration for obstructive sleep apnea. Others develop central apneas later, discovered on interrogation of their CPAP machine. The fact is, no one knows much about this so-called complex sleep apnea -- its natural course, prognosis / risks, and whether or how to treat it.

Cassel et al add valuable prospective longitudinal data to the discussion:

• 82 of 675 study patients (12%) had complex sleep apnea at initial polysomnography with CPAP.

• 436 patients were available for repeat PSG 3 months later.

• At 3 month repeat polysomnogram, only 14 still had complex sleep apnea. (But 28 of the original 82 were unavailable for follow-up.)

• However, 16 had developed new complex sleep apnea, for a total of 30 (6.9%).

• Those with complex sleep apnea were ~5 years older and had a 40% prevalence of coronary artery disease.

Sleep quality after initiation of CPAP was slightly worse in the complex sleep apnea patients -- they had more wakefulness after sleep onset. However, sleepiness was the same for those with and without complex sleep apnea. ERJ 2011;38:329-333.