• Jose-Alberto Palma, Jorge Iriarte, Secundino Fernandez, Miguel Valencia, Manuel Alegre, Julio Artieda, and Elena Urrestarazu.
• Sleep Unit, Clinical Neurophysiology Section, University Clinic of Navarra, Pamplona, Spain; Dysautonomia Center, Department of Neurology, New York University Medical Center, New York, USA.
• Clin Neurophysiol. 2014 Sep 1;125(9):1783-91.

ObjectiveThe pathophysiological basis of obstructive sleep apnea (OSA) is not completely understood and likely varies among patients. In this regard, some patients with OSA do not exhibit hypoxemia. We aimed to analyze the clinical, sleep, and autonomic features of a group of patients with severe OSA without hypoxia (OSA-h) and compare to OSA patients with hypoxia (OSA+h) and controls.MethodsFifty-six patients with OSA-h, 64 patients with OSA+h, and 44 control subjects were studied. Clinical and sleep features were analyzed. Besides, time- and frequency-domain heart rate variability (HRV) measures comprising the mean R-R interval, the standard deviation of the RR intervals (SDNN), the low frequency (LF) oscillations, the high frequency (HF) oscillations, and the LF/HF ratio, were calculated across sleep stages during a one-night polysomnography.ResultsOSA-h patients had a lower body mass index, a lower waist circumference, lower apnea duration, and a higher frequency of previous naso-pharyngeal surgery when compared to OSA+h patients. In terms of heart rate variability, OSA+h had increased LF oscillations (i.e., baroreflex function) during N1-N2 and rapid eye movement (REM) sleep when compared to OSA-h and controls. Both OSA+h and OSA-h groups had decreased HF oscillations (i.e., vagal inputs) during N1-N2, N3 and REM sleep when compared to controls. The LF/HF ratio was increased during N1-N2 and REM sleep, only in patients with OSA+h.ConclusionsPatients with OSA-h exhibit distinctive clinical, sleep, and autonomic features when compared to OSA with hypoxia.SignificanceOSA is a heterogeneous entity. These differences must be taken into account in future studies when analyzing therapeutic approaches for sleep apnea patients.Copyright © 2014 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

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