Within-night variation in respiratory effort preceding apnea termination and EEG delta power in sleep apnea.

We studied the within-night variability of the maximum esophageal pressure deflection before apnea termination (DPmax) in nine patients with severe obstructive sleep apnea as an index of the arousal threshold and the mean electroencephalogram (EEG) delta power for each 30 s as an index of the timing of sleep cycles. Periodicity in the time variation of delta power and DPmax was analyzed by determining their power spectral density and their relationship determined by cross correlation. DPmax and delta power varied cyclically and in phase with a major periodicity (major peak in power spectral density) of 117.6 +/- 8.8 (SE) min. The correlation between the values of DPmax and delta power was significant (P < 0.001) in each subject (mean r = 0.47 +/- 0.03), and the coherence between DPmax and delta power at their dominant frequency was high. Within cycles of non-rapid-eye-movement sleep, DPmax and delta power increased, reaching peak values on average at or after midcycle. These findings suggest that the arousal threshold to airway occlusion in patients with obstructive sleep apnea varies cyclically during the night synchronous to the underlying cycles of sleep.