Toschi-Dias E, Trombetta IC, Dias da Silva VJ, Maki-Nunes C, Cepeda FX, Alves MJ, Drager LF, Lorenzi-Filho G, Negrao CE, Rondon MU. Time delay of baroreflex control and oscillatory pattern of sympathetic activity in patients with metabolic syndrome and obstructive sleep apnea. Am J Physiol Heart Circ Physiol 304: H1038-H1044, 2013. First published January 25, 2013; doi:10.1152/ajpheart.00848.2012.-The incidence and strength of muscle sympathetic nerve activity (MSNA) depend on the magnitude (gain) and latency (time delay) of the arterial baroreflex control (ABR). However, the impact of metabolic syndrome (MetS) and obstructive sleep apnea (OSA) on oscillatory pattern of MSNA and time delay of the ABR of sympathetic activity is unknown. We tested the hypothesis that MetS and OSA would impair the oscillatory pattern of MSNA and the time delay of the ABR of sympathetic activity. Forty-three patients with MetS were allocated into two groups according to the presence of OSA (MetS ϩ OSA, n ϭ 21; and MetS Ϫ OSA, n ϭ 22). Twelve aged-paired healthy controls (C) were also studied. OSA (apnea-hypopnea index Ͼ 15 events/h) was diagnosed by polysomnography. We recorded MSNA (microneurography), blood pressure (beat-to-beat basis), and heart rate (EKG). Oscillatory pattern of MSNA was evaluated by autoregressive spectral analysis and the ABR of MSNA (ABR MSNA, sensitivity and time delay) by bivariate autoregressive analysis. Patients with MetS ϩ OSA had decreased oscillatory pattern of MSNA compared with MetS Ϫ OSA (P Ͻ 0.01) and C (P Ͻ 0.001). The sensitivity of the ABR MSNA was lower and the time delay was greater in MetS ϩ OSA compared with MetS Ϫ OSA (P Ͻ 0.001 and P Ͻ 0.01, respectively) and C (P Ͻ 0.001 and P Ͻ 0.001, respectively). Patients with MetS Ϫ OSA showed decreased oscillatory pattern of MSNA compared with C (P Ͻ 0.01). The sensitivity of the ABR MSNA was lower in MetS Ϫ OSA than in C group (P Ͻ 0.001). In conclusion, MetS decreases the oscillatory pattern of MSNA and the magnitude of the ABR MSNA. OSA exacerbates these autonomic dysfunctions and further increases the time delay of the baroreflex response of MSNA. latency of baroreflex control; muscle sympathetic nerve activity variability; heart rate variability SYMPATHETIC NERVE ACTIVITY is increased in patients with metabolic syndrome (MetS) (11,22), which enhances the risk of cardiovascular disease and likely cardiac death (5,20,21). Obstructive sleep apnea (OSA), a frequent comorbidity in patients with MetS (8), is characterized by recurrent episodes of partial or complete upper airway obstruction during sleep, leading to intermittent hypoxemia and frequent arousals from sleep (40). Additionally, OSA exacerbates the muscle sympathetic nerve activity (MSNA) in patients with MetS (12, 37) and impairs arterial baroreflex control (ABR) of heart rate (HR) (12, 37). Grassi et al. (12) demonstrated that ABR of HR was further decreased in patients with MetS and OSA. We confirmed that OSA exacerbates the dysfunction of the ABR of HR in patients with MetS (37).The ...