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Predictors of Decreased Spontaneous Baroreflex Sensitivity in Obstructive Sleep Apnea Syndrome^*

^* From the Sleep Research Laboratory (Drs. Ryan and McNicholas), St. Vincent’s University Hospital, Dublin, Ireland; and the Digital Signal Processing Research Group (Mr. Ward and Dr. Heneghan), Department of Electronic and Electrical Engineering, University College Dublin, Dublin, Ireland.

Correspondence to: Walter McNicholas, MD, FCCP, Department of Respiratory Medicine, St. Vincent’s University Hospital, Elm Park, Dublin 4, Ireland; e-mail: walter.mcnicholas{at}ucd.ie

Abstract

Background: The impact of obstructive sleep apnea syndrome (OSAS) on the arterial baroreflex, and its significance, is still under debate. We investigated the baroreflex sensitivity (BRS) during sleep in well-selected OSAS patient and control subject cohorts

Methods: We performed a prospective study of 10 non-OSAS subjects, 14 subjects with mild-to-moderate OSAS, and 14 male subjects with severe OSAS subjects. Groups were matched for age, body mass index, and other relevant variables. Subjects had no other disease and were not receiving regular medication. BP was monitored beat-by-beat (Portapres; Finapres Medical Systems; Amsterdam, the Netherlands) at night during polysomnography. Spontaneous BRS was assessed by the sequence technique. Heart-rate correction was also applied to calculate BRS at a heart rate (HR) of 60 beats/min (BRS-60) to account for intersubject variability in baseline HR. Eight suitable patients were treated with continuous positive airway pressure (CPAP), and BRS measurements were repeated 6 weeks later.

Results: BRS and BRS-60 were significantly lower in patients with severe OSAS than in patients with mild-to-moderate OSAS and in non-OSAS subjects, and a separate sleep-stage analysis revealed this difference to be evident in stage 2 non-rapid eye movement sleep and during nocturnal wakefulness. There was no difference in BRS and BRS-60 between non-OSAS subjects and patients with mild-to-moderate OSAS. In multivariate analysis, the desaturation index was the only independent predictor of depressed BRS. CPAP therapy significantly improved the BRS measures.

Conclusion: Patients with severe OSAS demonstrate depressed BRS during sleep, which may contribute to the cardiovascular pathophysiology in OSAS patients.

Key Words: baroreflex sensitivity • cardiovascular diseases • intermittent hypoxia • obstructive sleep apnea syndrome