Gupta A, et al. – The main purpose of the present study was to determine polysomnographic (PSG) characteristics, which may help predict the requirement for advanced therapeutic options for obstructive sleep apnea (OSA). Results of this study suggested that non–REM sleep instability and the presence of post–arousal central apneas could be important determinants of poor response to conventional positive airway pressure (PAP) and the requirement for advanced therapeutic options among patients with severe OSA.