Study Objectives: To evaluate NREM sleep instability, as measured by the cyclic alternating pattern (CAP), in a cohort of children with mild sleep disordered breathing (SDB) or frank obstructive sleep apnea (OSA) and normal controls. Design: Prospective study. Settings: Sleep laboratory in academic center. Participants: Twenty-two patients (13 boys; mean age 6.5±2.4 years; 10 with mild SDB and 12 with OSA) and 15 normal children matched for age underwent overnight polysomnographic recordings in

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... a standard laboratory setting. Sleep was visually scored for sleep macrostructure and CAP in a blinded fashion using standard criteria. Markovian analysis was also performed. Measurements and results: Participants with OSA had reduced total CAP rates than normal controls and mild SDB patients. Children with mild SDB or OSA had a lower number of A1, lower A1 percentage, and lower A1 index than controls. Children with OSA also showed longer intervals between consecutive A phases and a decrease in entropy in the Markovian analysis. Conclusions: The lower CAP rate and its reduced entropy in children with mild SDB or OSA seem to indicate the presence of subtle sleep alterations that are not clearly identifiable with other approaches and might provide more robust correlates of neurocognitive and behavioral dysfunction in snoring children.