In order to study the relationship between sleep-induced periodic breathing and the development of occlusive sleep apneas, 6 patients with hypersomnia-sleep apnea syndrome were studied during nocturnal sleep before and approximately 1 month after therapeutic tracheostomy. Post-tracheostomy studies were performed in open and closed tracheostomy states. Sleep-induced periodic breathing resembling the pattern of Cheyne-Stokes breathing was observed in all patients before and after tracheostomy, even when tracheostomy was left open. When tracheostomy was closed all patients developed periodic hypopneas with significant oxygen desaturation, and 4 patients developed occlusive apneas at the nadir of the periodic changes. However, apnea and desaturation indexes during closed tracheostomy were significantly lower than their respective pretracheostomy values. These results indicate that sleep-induced periodic breathing, which represents an instability of respiratory control, is primary to the development of occlusive apneas, and the periodically observed is exaggerated by hypoxemia. Comparison of pre- and post-tracheostomy studies indicate a significant improvement in the underlying disorder most likely caused by the elimination of nocturnal hypoxemia and sleep fragmentation.