Within-night repeatability and long-term consistency of sleep apnea endotypes: the Multi-Ethnic Study of Atherosclerosis and Osteoporotic Fractures in Men Study

Study Objectives Obstructive sleep apnea (OSA) is characterized by multiple "endotypic traits," including pharyngeal collapsibility, muscle compensation, loop gain, and arousal threshold. Here, we examined (1) within-night repeatability, (2) long-term consistency, and (3) influences of body position and sleep state, of endotypic traits estimated from in-home polysomnography in mild-to-severe OSA (apnea-hypopnea index, AHI > 5 events/h). Methods Within-night repeatability was assessed using Multi-Ethnic Study of Atherosclerosis (MESA): Traits derived separately from "odd" and "even" 30-min periods were correlated and regression (error vs. N windows available) provided a recommended amount of data for acceptable repeatability (R-threshold = 0.7). Long-term consistency was assessed using the Osteoporotic Fractures in Men Study (MrOS) at two time points 6.5 +/- 0.7 years apart, before and after accounting for across-year body position and sleep state differences. Within-night dependence of traits on position and state (MESA plus MrOS data) was estimated using bootstrapping. Results Within-night repeatability for traits ranged from R = 0.62-0.79 and improved to R = 0.69-0.83 when recommended amounts of data were available (20-35 7-min windows, available in 94%-98% of participants); repeatability was similar for collapsibility, loop gain, and arousal threshold (R = 0.79-0.83), but lower for compensation (R = 0.69). Long-term consistency was modest (R = 0.30-0.61) and improved (R = 0.36-0.63) after accounting for position and state differences. Position/state analysis revealed reduced loop gain in REM and reduced collapsibility in N3. Conclusions Endotypic traits can be obtained with acceptable repeatability. Long-term consistency was modest but improved after accounting for position and state changes. These data support the use of endotypic assessments in large-scale epidemiological studies.