Association between sleep microarchitecture and cognition in obstructive sleep apnea.

STUDY OBJECTIVES: Obstructive sleep apnea (OSA) increases the risk of cognitive impairment. Measures of sleep microarchitecture from EEG may help identify patients at risk of this complication. METHODS: Participants with suspected OSA (n=1142) underwent in-laboratory polysomnography and completed sleep and medical history questionnaires, and tests of global cognition (Montreal Cognitive Assessment, MoCA), memory (Rey Auditory Verbal Learning Test, RAVLT) and information processing speed (Digit-Symbol Coding, DSC). Associations between cognitive scores and stage 2 NREM sleep spindle density, power, frequency and %-fast (12-16Hz), odds-ratio product (ORP), normalized EEG power (EEGNP) and the delta:alpha ratio were assessed using multivariable linear regression (MLR) adjusted for age, sex, education, and total sleep time. Mediation analyses were performed to determine if sleep microarchitecture indices mediate the negative effect of OSA on cognition. RESULTS: All spindle characteristics were lower in participants with moderate and severe OSA (p≤0.001, versus no/mild OSA) and positively associated with MoCA, RAVLT and DSC scores (false discovery rate corrected p-value, q≤0.026), except spindle power which was not associated with RAVLT (q=0.185). ORP during NREM sleep (ORPNREM) was highest in severe OSA participants (p≤0.001) but neither ORPNREM (q≥0.230) nor the delta:alpha ratio were associated with cognitive scores in MLR analyses (q≥0.166). In mediation analyses, spindle density and EEGNP (p≥0.048) mediated moderate-to-severe OSA's negative effect on MoCA scores while ORPNREM, spindle power and %-fast spindles mediated OSA's negative effect on DSC scores (p≤0.018). CONCLUSION: Altered spindle activity, ORP and normalized EEG power may be important contributors to cognitive deficits in patients with OSA.

Feasibility and Acceptability of Using Wireless Limited Polysomnography to Capture Sleep Before, During, and After Hospitalization for Patients With Planned Cardiothoracic Surgery.

BACKGROUND: Sleep disruption, a common symptom among patients requiring cardiovascular surgery, is a potential risk factor for the development of postoperative delirium. Postoperative delirium is a disorder of acute disturbances in cognition associated with prolonged hospitalization, cognitive decline, and mortality. OBJECTIVE: The aim of this study was to evaluate the feasibility and acceptability of using polysomnography (PSG) to capture sleep in patients with scheduled cardiothoracic surgery. METHODS: Wireless limited PSG assessed sleep at baseline (presurgery at home), postoperatively in the intensive care unit, and at home post hospital discharge. Primary outcomes were quality and completeness of PSG signals, and acceptability by participants and nursing staff. RESULTS: Among 15 patients, PSG data were of high quality, and mean percentage of unscorable data was 5.5% ± 11.1%, 3.7% ± 5.4%, and 3.7% ± 8.4% for baseline, intensive care unit, and posthospitalization measurements, respectively. Nurses and patients found the PSG monitor acceptable. CONCLUSIONS: Wireless, limited PSG to capture sleep across the surgical continuum was feasible, and data were of high quality. Authors of future studies will evaluate associations of sleep indices and development of postoperative delirium in this high-risk population.

An approach for determining the reliability of manual and digital scoring of sleep stages.

STUDY OBJECTIVES: Inter-scorer variability in sleep staging is largely due to equivocal epochs that contain features of more than one stage. We propose an approach that recognizes the existence of equivocal epochs and evaluates scorers accordingly. METHODS: Epoch-by-epoch staging was performed on 70 polysomnograms by six qualified technologists and by a digital system (Michele Sleep Scoring [MSS]). Probability that epochs assigned the same stage by only two of the six technologists (minority score) resulted from random occurrence of two errors was calculated and found to be <5%, thereby indicating that the stage assigned is an acceptable variant for the epoch. Acceptable stages were identified in each epoch as stages assigned by at least two technologists. Percent agreement between each technologist and the other five technologists, acting as judges, was determined. Agreement was considered to exist if the stage assigned by the tested scorer was one of the acceptable stages for the epoch. Stage assigned by MSS was likewise considered in agreement if included in the acceptable stages made by the technologists. RESULTS: Agreement of technologists tested against five qualified judges increased from 80.8% (range 70.5%-86.4% among technologists) when using the majority rule, to 96.1 (89.8%-98.5%) by the proposed approach. Agreement between unedited MSS and same judges was 90.0% and increased to 92.1% after brief editing. CONCLUSIONS: Accounting for equivocal epochs provides a more accurate estimate of a scorer's (human or digital) competence in scoring sleep stages and reduces inter-scorer disagreements. The proposed approach can be implemented in sleep-scoring training and accreditation programs.

Contribution of obstructive sleep apnea to disrupted sleep in a large clinical cohort of patients with suspected obstructive sleep apnea.

STUDY OBJECTIVES: The response of sleep depth to CPAP in patients with OSA is unpredictable. The odds-ratio-product (ORP) is a continuous index of sleep depth and wake propensity that distinguishes different sleep depths within sleep stages, and different levels of vigilance during stage wake. When expressed as fractions of time spent in different ORP deciles, nine distinctive patterns are found. Only three of these are associated with OSA. We sought to determine whether sleep depth improves on CPAP exclusively in patients with these three ORP patterns. METHODS: ORP was measured during the diagnostic and therapeutic components of 576 split-night polysomnographic (PSG) studies. ORP architecture in the diagnostic section was classified into one of the nine possible ORP patterns and the changes in sleep architecture were determined on CPAP for each of these patterns. ORP architecture was similarly determined in the first half of 760 full-night diagnostic PSG studies and the changes in the second half were measured to control for differences in sleep architecture between the early and late portions of sleep time in the absence of CPAP. RESULTS: Frequency of the three ORP patterns increased progressively with the apnea-hypopnea index. Sleep depth improved significantly on CPAP only in the three ORP patterns associated with OSA. Changes in CPAP in the other six patterns, or in full diagnostic PSG studies, were insignificant or paradoxical. CONCLUSIONS: ORP architecture types can identify patients in whom OSA adversely affects sleep and whose sleep is expected to improve on CPAP therapy.

Sleep architecture based on sleep depth and propensity: patterns in different demographics and sleep disorders and association with health outcomes.

STUDY OBJECTIVES: Conventional metrics of sleep quantity/depth have serious shortcomings. Odds-Ratio-Product (ORP) is a continuous metric of sleep depth ranging from 0 (very deep sleep) to 2.5 (full-wakefulness). We describe an ORP-based approach that provides information on sleep disorders not apparent from traditional metrics. METHODS: We analyzed records from the Sleep-Heart-Health-Study and a study of performance deficit following sleep deprivation. ORP of all 30-second epochs in each PSG and percent of epochs in each decile of ORPs range were calculated. Percentage of epochs in deep sleep (ORP < 0.50) and in full-wakefulness (ORP > 2.25) were each assigned a rank, 1-3, representing first and second digits, respectively, of nine distinct types ("1,1", "1,2" … "3,3"). Prevalence of each type in clinical groups and their associations with demographics, sleepiness (Epworth-Sleepiness-Scale, ESS) and quality of life (QOL; Short-Form-Health-Survey-36) were determined. RESULTS: Three types ("1,1", "1,2", "1,3") were prevalent in OSA and were associated with reduced QOL. Two ("1,3" and "2,3") were prevalent in insomnia with short-sleep-duration (insomnia-SSD), but only "1,3" was associated with poor sleep depth and reduced QOL, suggesting two phenotypes in insomnia-SSD. ESS was high in types "1,1" and "1,2", and low in "1,3" and "2,3". Prevalence of some types increased with age while in others it decreased. Other types were either rare ("1,1" and "3,3") or high ("2,2") at all ages. CONCLUSIONS: The proposed ORP histogram offers specific and unique information on the underlying neurophysiological characteristics of sleep disorders not captured by routine metrics, with potential of advancing diagnosis and management of these disorders.

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/m², 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. 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.