Abstract
STUDY OBJECTIVES: The Odds Ratio Product (ORP) is an objective measure of sleep depth using the relationships of the powers of different electroencephalogram (EEG) frequencies in a single index. The range of the ORP is 0 (deeply asleep) to 2.5 (fully awake). This investigation seeks to elucidate normal values of non-rapid eye movement ORP (ORP(NR)) in healthy individuals, repeatability of the measure, and the change in ORP(NR) following continuous positive airway pressure (CPAP) treatment. METHODS: Healthy individuals underwent a home sleep apnea test (HSAT) with EEG followed 1 week later by EEG alone. Another cohort with OSA underwent baseline HSAT with EEG followed by a second EEG study approximately 4 weeks into treatment with CPAP. RESULTS: Thirty-eight healthy individuals completed the protocol (mean age of 34.9 ± 7.4 years, Epworth Sleepiness Scale score 3.6 ± 2.4, Insomnia Severity Index score 2.0 ± 1.6 and Functional Outcomes of Sleep Questionnaire - shorter version score 19 ± 1.2). The mean ORP(NR) for all nights was 0.52 ± 0.13. The difference between the first night and the second night was 0.024 ± 0.17 (not significant). The intraclass correlation coefficient was 0.525, suggesting only moderate agreement between the first and second nights. The normal value for ORP(NR) in healthy individuals is ≤ 0.78 units using two standard deviations as the cutoff. Forty participants completed the OSA protocol (mean age 49 ± 11 years, body mass index 35 ± 6 kg/m², apnea-hypopnea index 33.5 ± 28.4 events/h). The mean pre-CPAP ORP(NR) was 0.69 ± 0.24 and the mean post-CPAP ORP(NR) was 0.57 ± 0.22 (P = .02). CONCLUSIONS: The ORP(NR) proves to have significant variability from night to night in healthy individuals. ORP(NR) objectively improves following CPAP treatment, providing further evidence that it measures sleep depth. CITATION: Penner CG, Gerardy B, Ryan R, Williams M. The odds ratio product (an objective sleep depth measure): normal values, repeatability, and change with CPAP in patients with OSA. J Clin Sleep Med. 2019;15(8):1155-1163.