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Polysomnography (PSG) findings in a patient with obstructive sleep apnea (OSA). The PSG findings obtained from a 60-year-old patient with severe OSA (apnea-hypopnea index 60) are shown. Note that SpO2 repeatedly decreases and then increases with a cyclic variation of heart rate (CVHR). ECG, electrocardiogram; RR, R-R interval.
