Human Gamma Oscillations during Slow Wave Sleep

Neocortical local field potentials have shown that gamma oscillations occur spontaneously during slow-wave sleep (SWS). At the macroscopic EEG level in the human brain, no evidences were reported so far. In this study, by using simultaneous scalp and intracranial EEG recordings in 20 epileptic subjects, we examined gamma oscillations in cerebral cortex during SWS. We report that gamma oscillations in low (30–50 Hz) and high (60–120 Hz) frequency bands recurrently emerged in all investigated regions and their amplitudes coincided with specific phases of the cortical slow wave. In most of the cases, multiple oscillatory bursts in different frequency bands from 30 to 120 Hz were correlated with positive peaks of scalp slow waves (“IN-phase” pattern), confirming previous animal findings. In addition, we report another gamma pattern that appears preferentially during the negative phase of the slow wave (“ANTI-phase” pattern). This new pattern presented dominant peaks in the high gamma range and was preferentially expressed in the temporal cortex. Finally, we found that the spatial coherence between cortical sites exhibiting gamma activities was local and fell off quickly when computed between distant sites. Overall, these results provide the first human evidences that gamma oscillations can be observed in macroscopic EEG recordings during sleep. They support the concept that these high-frequency activities might be associated with phasic increases of neural activity during slow oscillations. Such patterned activity in the sleeping brain could play a role in off-line processing of cortical networks

Exhaled Nitric Oxide as a Surrogate Marker for Obstructive Sleep Apnea Severity Grading: An In-Hospital Population Study

Khue Dang-Thi-Mai,1 Nhat-Nam Le-Dong,2 Vu Le-Thuong,1 Ngoc Tran-Van,1 Sy Duong-Quy3,4 1Department of Respiratory Diseases, Cho Ray Hospital, Ho Chi Minh City, Vietnam; 2Department of Technology, Sunrise, Namur, Belgium; 3Bio-Medical Research Centre, Lam Dong Medical College, Dalat, Vietnam; 4Penn State Medical College, Hershey Medical Center, Hershey, PA, USACorrespondence: Sy Duong-QuyBio-Medical Research Centre, Lam Dong Medical College, 16 Ngo Quyen, Dalat, VietnamTel +84 918413813Fax +84 2633815000Email [email protected]: Our study aimed to evaluate the relationship between exhaled nitric oxide (eNO) markers and obstructive sleep apnea (OSA) severity and verify the changes in eNO profiles among mild, moderate, and severe OSA subgroups.Methods: This study was a cross-sectional and in-hospital population-based study. We investigated 123 OSA patients (17 mild, 23 moderate and, 83 severe OSA) in the department of respiratory diseases. Studied data included anthropometry, respiratory polygraphy, biological markers, spirometry, and multi-flow eNO measurements. Data analysis implied linear correlation, non-parametric ANOVA, and pair-wise comparison.Results: No significant difference could be found among 3 OSA severity subgroups for FENO at – four sampling flow rates (50– 350 mL/s). The bronchial production rate of NO (J’awNO) was proportionally increased, with median values of 11.2, 33.9, and 36.2 in mild, moderate, and severe OSA, respectively (p=0.010). The alveolar concentration of NO (CANO) changed with a non-linear pattern; it was increased in moderate (6.49) vs mild (7.79) OSA but decreased in severe OSA (5.20, p = 0.015). The only correction that could be established between OSA severity and exhaled nitric oxide markers is through J’AWNO (rho=0.25, p=0.02) and CANO (rho= 0.18, p=0.04). There was no significant correlation between FENO measured at three different flow rates and the OSA severity. We also found a weak but significant correlation between FENO 100 and averaged SpO2 (rho = 0.07, p= 0.03).Conclusion: The present study showed that J’AWNO, which represents eNO derived from the central airway, is proportionally increased in more severe OSA, while eNO from alveolar space, indicated by CANO, was also associated with OSA severity and relatively lower in the most severe OSA patients. In contrast, stand-alone FENO metrics did not show a clear difference among the three severity subgroups.Keywords: exhaled nitric oxide, FENO, J’AWNO, CANO, obstructive sleep apne