Obstructive Sleep Apnea Impairs Postexercise Sympathovagal Balance in Patients with Metabolic Syndrome

Study Objectives: The attenuation of heart rate recovery after maximal exercise (Delta HRR) is independently impaired by obstructive sleep apnea (OSA) and metabolic syndrome (MetS). Therefore, we tested the hypotheses: (1) MetS + OSA restrains Delta HRR; and (2) Sympathetic hyperactivation is involved in this impairment. Design: Cross-sectional study. Participants: We studied 60 outpatients in whom MetS had been newly diagnosed (ATP III), divided according to apnea-hypopnea index (AHI) >= 15 events/h in MetS + OSA (n = 30, 49 +/- 1.7 y) and AHI < 15 events/h in MetS - OSA (n = 30, 46 +/- 1.4 y). Normal age-matched healthy control subjects (C) without MetS and OSA were also enrolled (n = 16, 46 +/- 1.7 y). Interventions: Polysomnography, microneurography, cardiopulmonary exercise test. Measurements and Results: We evaluated OSA (AHI - polysomnography), muscle sympathetic nerve activity (MSNA - microneurography) and cardiac autonomic activity (LF = low frequency, HF = high frequency, LF/HF = sympathovagal balance) based on spectral analysis of heart rate (HR) variability. Delta HRR was calculated (peak HR minus HR at first, second, and fourth minute of recovery) after cardiopulmonary exercise test. MetS + OSA had higher MSNA and LF, and lower HF than MetS - OSA and C. Similar impairment occurred in MetS - OSA versus C (interaction, P < 0.01). MetS + OSA had attenuated Delta HRR at first, second, and at fourth minute than did C, and attenuated Delta HRR at fourth minute than did MetS - OSA (interaction, P < 0.001). Compared with C, MetS - OSA had attenuated Delta HRR at second and fourth min (interaction, P < 0.001). Further analysis showed association of the Delta HRR (first, second, and fourth minute) and AHI, MSNA, LF and HF components (P < 0.05 for all associations). Conclusions: The attenuation of heart rate recovery after maximal exercise is impaired to a greater degree where metabolic syndrome (MetS) is associated with moderate to severe obstructive sleep apnea (OSA) than by MetS with no or mild or no OSA. This is at least partly explained by sympathetic hyperactivity.