Background: Sleep-disordered breathing (SDB) is an independent risk factor for cardiovascular morbidity. Dysfunction of the cardiovascular autonomic nervous system may be a potential mechanism whereby SDB is linked to cardiovascular disease. Repetitive sympathetic activation during apneic episodes may impair cardiovascular reflex function, and increased sympathetic activity can stimulate renin release. Given that patients with SDB may have reduced cardiovascular autonomic function, the purpose of this study was to determine whether treatment with continuous positive airway pressure (CPAP) for 6 weeks would improve autonomic function.
Methods: Twenty-nine participants with a diagnosis of SDB, who completed 6 weeks of CPAP therapy, were evaluated for cardiovascular autonomic nerve fiber function at baseline and post therapy. Autonomic function tests included the following: R-R interval variation during deep breathing measured by vector analysis (ie, mean circular resultant [MCR]) and expiration/inspiration (E/I) ratio; and the Valsalva maneuver. Participants were also evaluated prior to CPAP therapy for plasma renin activity levels.
Results: Participants in this study showed improved cardiovascular autonomic function after 6 weeks of treatment (baseline vs follow-up) as assessed by the mean (± SD) MCR (33.2 ± 22.5 vs 36.9 ± 24.2, respectively; p < 0.05) and E/I ratio (1.20 ± 0.12 vs 1.24 ± 0.14, respectively; p < 0.01). Improved vagal tone was also noted for subjects with elevated renin levels.
Conclusions: Treatment of SDB with CPAP for 6 weeks improved vagal tone and may be beneficial in reducing the risk of developing clinical manifestations of cardiovascular autonomic dysfunction (eg, increased risk of mortality).