Exclusion of EEG-based arousals in wake epochs of polysomnography leads to underestimation of the arousal index

Abstract

Study Objectives: There is an internal contradiction in current American Academy of Sleep Medicine standards for arousal index (AI) calculation in polysomnography: Arousals in sleep and wake epochs are counted, but only sleep time is used in the denominator. This study aimed to investigate the impact of including arousals scored in wake epochs on the AI. Methods: We compared AIs including (AIinc) vs excluding (AIexc) awake-epoch arousals from 100 consecutive polysomnograms conducted for investigation of possible obstructive sleep apnea. To determine the AI that most closely approximated “truth,” AIinc and AIexc were compared to an AI calculated from continuous sleep analysis (AIcont) in a 20-polysomnogram subgroup of patients. Results: The median (interquartile range) increase in AIinc was 5.2 events/h (3.5–8.1) vs AIexc (AIinc = 28.0 events/h [18.4–38.9] vs AIexc = 22.9 events/ h [13.1–31.3]), equating to an increase of 25.3% (15.6–40.8). As the AI increased, the difference increased (P