Background: There is little evidence of how metabolic syndrome (MS) affects sympathovagal balance responses to acute physical effort (APE) and autonomic stimulation (AS). This study aimed to evaluate the heart rate variability (HRV) responses to the combined APE and AS challenges.
Methods: Fourteen subjects (8 men; 49.15 ± 8.67 years) divided into two groups: 7 healthy volunteers [control group (CG)] and 7 patients with MS. Sympathovagal balance [low frequency (LF)/high frequency (HF) ratio] was accessed by HRV through the beat-to-beat heart rate (HR) electrocardiogram. Other variables analyzed were as follows: HR, RR-interval variance (VAR/ms2), LF and HF normalized units (un). The APE consisted of a 30-min walk at 65%-75% of the age-predicted maximal HR. The AS was achieved by changing from the supine to standing position (activity orthostatic position).
Results: At rest, all HRV variables differ with on MS, but after APE and AS LF (nu) and HF (nu) become similar to the CG. However, the LF/HF ratio responses to the AS were significantly different after APE, but only in the MS (CG rest: 367% ± 59% vs. recovery 495% ± 116%, P > 0.05; MS rest: 316% ± 88% vs. recovery: 665% ± 165%; P = 0.045). Comparing the difference between AS in rest and recovery (ΔAS = rest - recovery), the LF/HF ratio was notably higher in the MS group (CG: 94% ± 29% vs. MS: 415% ± 76%; P < 0.0001).
Conclusions: The APE and AS induced by body posture changes activated a clear distinction in sympathovagal balance response in MS.
Keywords: autonomic nervous system; cardiac risk factors; exercise test; heart rate control; metabolic syndrome.