Obstructive sleep apnea (OSA) is thought to affect almost 1 billion people worldwide. OSA has well established cardiovascular and neurocognitive sequelae, although the optimal metric to assess its severity and/or potential response to therapy remains unclear. The apnea-hypopnea index (AHI) is well established; thus, we review its history and predictive value in various different clinical contexts. Although the AHI is often criticized for its limitations, it remains the best studied metric of OSA severity, albeit imperfect. We further review the potential value of alternative metrics including hypoxic burden, arousal intensity, odds ratio product, and cardiopulmonary coupling. We conclude with possible future directions to capture clinically meaningful OSA endophenotypes including the use of genetics, blood biomarkers, machine/deep learning and wearable technologies. Further research in OSA should be directed towards providing diagnostic and prognostic information to make the OSA diagnosis more accessible and to improving prognostic information regarding OSA consequences, in order to guide patient care and to help in the design of future clinical trials.

To evaluate long-term safety and maintenance of efficacy of solriamfetol treatment for excessive daytime sleepiness in narcolepsy and obstructive sleep apnea (OSA). Participants with narcolepsy or OSA who completed a prior solriamfetol study were eligible. A 2-week titration period was followed by a maintenance phase (up to 50 weeks). Efficacy was assessed by Epworth Sleepiness Scale (ESS) and Patient and Clinical Global Impression of Change (PGI-C and CGI-C, respectively). After approximately 6 months of treatment, a subgroup entered a 2-week placebo-controlled randomized withdrawal (RW) phase. Change in ESS from beginning to end of the RW phase was the primary endpoint; PGI-C and CGI-C were secondary endpoints. Safety was assessed throughout the study. In the maintenance phase, solriamfetol-treated participants demonstrated clinically meaningful improvements on ESS, PGI-C, and CGI-C. In the RW phase, least squares mean change on ESS was 1.6 in participants continuing solriamfetol versus 5.3 in participants switched to placebo (p < .0001). For both secondary endpoints, higher percentages of participants receiving placebo were reported as worse at the end of the RW phase versus solriamfetol (p < .0001). Common treatment-emergent adverse events (TEAEs) with solriamfetol were headache, nausea, nasopharyngitis, insomnia, dry mouth, anxiety, decreased appetite, and upper respiratory tract infection; 27 (4.2%) participants experienced at least one serious TEAE, and 61 (9.5%) withdrew because of TEAEs. This study demonstrated long-term maintenance of efficacy of solriamfetol under open-label and double-blind, placebo-controlled conditions. Safety profile of solriamfetol was consistent with previous 12-week studies; no new safety concerns were identified. NCT02348632