Reproducibility and predictors of the apnea hypopnea index across multiple nights.

Background: Attended polysomnography (PSG) is the standard diagnostic test for sleep apnea (SA). However, due to internight variability in SA, a single night PSG may not accurately reflect the true severity of SA. Although internight variability is a well-known phenomenon, its root causes have not been fully elucidated. The objective of this study was to determine factors associated with internight variability in the apnea-hypopnea index (AHI) and its magnitude in the home environment.

Methods: Each participant had a full overnight PSG simultaneous with a validated portable sleep apnea monitoring device (BresoDx® ) followed by two overnight home tests using the portable monitor only. Patients were stratified into those with variable AHI and consistent AHI (AHI difference ≥10 or <10 between any 2 nights, respectively). Demographics, sleepiness, sleep test variable, and supine-predominant SA (supine-SA) were examined for any association with variable AHI.

Results: Forty patients completed the protocol. The correlation between PSG and simultaneous BresoDx derived AHIs was 93.4%. Inter-class correlation between the three nights' AHIs was 89.2%. Over two-thirds (67.5%) of patients had consistent AHIs across the three nights while 32.5% had variable AHI. AHI variability was significantly associated with supine-SA ( p =0.0014) and correlated with first night's AHI (r=0.664, p <0.001). None of the other variable, including BMI, sleepiness, gender, or test duration were associated with internight variability.

Conclusion: Although portable monitoring was highly reproducible over three nights in the majority of participants, one third had a variable AHI. Supine-SA and high AHI on the first night were predictors of high internight variability.