• W B Mendelson.
• Department of Neurology, Cleveland Clinic Foundation, OH 44195.
• Cleve Clin J Med. 1994 Jul 1;61(4):299-303.

BackgroundSleep-disordered breathing appears to vary widely from night to night in the general population.ObjectiveTo determine the difference in accuracy of diagnosing sleep apnea when there are one vs two sleep recordings in a clinical population.MethodsFifty patients clinically suspected of having obstructive sleep apnea underwent polysomnography for two nights.ResultsThe number of episodes of apnea or hypopnea per hour (the apnea-hypopnea index, AHI) on each night was highly correlated (r = .86), and there were no significant differences between the two nights in duration of episodes, mean minimal arterial oxygen desaturation, or absolute minimum desaturation. On the first night, 46 patients had an AHI of 5 or more; on the second night 49 did. Similarly, 42 patients had an AHI of 10 or more on the first night; on the second night 46 did. All patients with an AHI of 5 or more on the first night also had an AHI of 5 or more the second night, and only one patient who had an AHI of 10 or more on the first night did not on the second night. In contrast, some nonrespiratory variables improved on the second night.ConclusionsOne night of testing should generally suffice. A second recording might be expected to be positive in half of the small group of patients clinically suspected of having sleep apnea who have a negative first study.

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