Sands SA, et al. - This study was undertaken to determine if elevated loop gain and three key endophenotypic traits (collapsibility/compensation/arousability)—quantified using clinical polysomnography—can predict the effect of supplemental oxygen on obstructive sleep apnea (OSA) severity. For this investigation, 36 subjects (apnea-hypopnea index [AHI] >20 events/h) completed two overnight polysomnographic studies (single-blinded randomised-controlled cross-over) on supplemental oxygen (40% inspired) vs sham (air). Using diagnostic polysomnography, patients whose OSA responds to supplemental oxygen could be identified by measuring their endophenotypic traits.