Sleep
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It has recently been described that the maximal respiratory effort developed at the end of an apnea (Pesmax)--which is regarded as an index of arousal threshold in patients with obstructive sleep apnea syndrome (OSA)--increases progressively during the night, probably as a consequence of associated sleep fragmentation. In order to find out whether the nocturnal trend of Pesmax may be more influenced by a sleep-dependent circadian rhythm than by sleep fragmentation, we revised the polygraphic recordings of 37 patients in whom obstructive apneas were recorded for at least 7 hours. In 15 of these patients, analysis was made for eight hours of the night. ⋯ Considering the slope of Pesmax changes across the night, we saw that neither the apnea+hypopnea index nor the indices of sleep fragmentation affected the nocturnal trend. The present data demonstrate the presence of a nocturnal trend in arousal threshold in OSA patients independent of sleep fragmentation. The biphasic evolution of the arousal threshold may be caused by factors that influence the circadian and homeostatic processes.