Figure 1.

Mean R-R interval, standard deviation of the NN interval (SDNN), ultra low-frequency components (ULF), very low-frequency components (VLF), low-frequency components (LF), and high-frequency components (HF) during different sleep stages (N1-N2, N3, REM) as well as during wakefulness before (W-pre) and after (W-post) sleep in patients with SRAH, patients with OSA, and control patients. Asterisks indicate statistical significance, and the analysis of variance P value is given. OSA, obstructive sleep apnea; REM, rapid eye movement; SRAH, sleep related alveolar hypoventilation.