Altered K-complex morphology during sustained inspiratory airflow limitation is associated with next-day lapses in vigilance in obstructive sleep apnea

• Published in: Sleep (New York, N.Y.) Vol. 44; no. 7; p. 1
• Main Authors: Parekh, Ankit, Kam, Korey, Mullins, Anna E, Castillo, Bresne, Berkalieva, Asem, Mazumdar, Madhu, Varga, Andrew W, Eckert, Danny J, Rapoport, David M, Ayappa, Indu
• Format: Journal Article
• Language: English
• Published: US Oxford University Press 01.07.2021
• Subjects: Analysis; Continuous Positive Airway Pressure; Electroencephalography; Health aspects; Humans; Morphology; Polysomnography; Sleep; Sleep apnea; Sleep apnea syndromes; Sleep Apnea, Obstructive - therapy; Sleep Disordered Breathing; Wakefulness; vigilance; upper airway resistance syndrome; sleep disordered breathing; inspiratory flow limitation; EEG; alpha; delta; sleep apnea
• ISSN: 0161-8105; 1550-9109
• DOI: 10.1093/sleep/zsab010

Abstract Study Objectives Determine if changes in K-complexes associated with sustained inspiratory airflow limitation (SIFL) during N2 sleep are associated with next-day vigilance and objective sleepiness. Methods Data from thirty subjects with moderate-to-severe obstructive sleep apnea who completed three in-lab polysomnograms: diagnostic, on therapeutic continuous positive airway pressure (CPAP), and on suboptimal CPAP (4 cmH2O below optimal titrated CPAP level) were analyzed. Four 20-min psychomotor vigilance tests (PVT) were performed after each PSG, every 2 h. Changes in the proportion of spontaneous K-complexes and spectral characteristics surrounding K-complexes were evaluated for K-complexes associated with both delta (∆SWAK), alpha (∆αK) frequencies. Results Suboptimal CPAP induced SIFL (14.7 (20.9) vs 2.9 (9.2); %total sleep time, p < 0.001) with a small increase in apnea–hypopnea index (AHI3A: 6.5 (7.7) vs 1.9 (2.3); p < 0.01) versus optimal CPAP. K-complex density (num./min of stage N2) was higher on suboptimal CPAP (0.97 ± 0.7 vs 0.65±0.5, #/min, mean ± SD, p < 0.01) above and beyond the effect of age, sex, AHI3A, and duration of SIFL. A decrease in ∆SWAK with suboptimal CPAP was associated with increased PVT lapses and explained 17% of additional variance in PVT lapses. Within-night during suboptimal CPAP K-complexes appeared to alternate between promoting sleep and as arousal surrogates. Electroencephalographic changes were not associated with objective sleepiness. Conclusions Sustained inspiratory airflow limitation is associated with altered K-complex morphology including the increased occurrence of K-complexes with bursts of alpha as arousal surrogates. These findings suggest that sustained inspiratory flow limitation may be associated with nonvisible sleep fragmentation and contribute to increased lapses in vigilance.