The Odds Ratio Product (An Objective Sleep Depth Measure): Normal Values, Repeatability, and Change With CPAP in Patients With OSA

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 (ORPNR) in healthy individuals, repeatability of the measure, and the change in ORPNR 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 ORPNR 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 ORPNR 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/m(2), apnea-hypopnea index 33.5 +/- 28.4 events/h). The mean pre-CPAP ORPNR was 0.69 +/- 0.24 and the mean post-CPAP ORPNR was 0.57 +/- 0.22 (P = .02). Conclusions: The ORPNR proves to have significant variability from night to night in healthy individuals. ORPNR objectively improves following CPAP treatment, providing further evidence that it measures sleep depth.