Neuroadrenergic activation in obstructive sleep apnea syndrome: a systematic review and meta-analysis

BACKGROUND: Neuroadrenergic overdrive occurs in obstructive sleep apnea syndrome (OSAS). However, the small sample size of the microneurographic studies, heterogeneity of the patients examined, presence of comorbidities, represented major weaknesses not allowing to precisely define the main features of the phenomenon, particularly in nonobese patients. OBJECTIVE: This meta-analysis evaluated 850 participants recruited in 26 microneurographic studies, based on muscle sympathetic nerve activity (MSNA) quantification in uncomplicated OSAS of different clinical severity. METHODS: The evaluation was extended to the relationships of MSNA with heart rate (HR), anthropometric and blood pressure (BP) values, metabolic variables, apnea-hypopnea index (AHI) and oxygen saturation. RESULTS: MSNA is activated markedly and almost homogeneously between studies, showing a progressive increase from the healthy state to mild, moderate and severe OSAS (41.6, 48.3, 65.5 and 70.7 bursts/100 heart beats, respectively, P < 0.01). Of special interest are the findings that first, MSNA is significantly related to the AHI, a marker of OSAS severity (r = 0.55, P < 0.02) and O2 saturation but not to body weight and BMI, as it occurs in OSAS associated with obesity; and second, HR is significantly and directly related to MSNA and AHI (r = 0.56 and 0.46, P < 0.03 for both), thus representing a surrogate marker of the sympathetic overdrive. CONCLUSION: OSAS, even when uncomplicated by other cardiometabolic disease, displays a marked sympathetic activation, reflected by the MSNA and HR behavior, becoming a target of therapeutic interventions aimed at exerting sympathomoderating effects, such as continuous positive airway pressure.