Heart rate reduction and autonomic response in young adults following different vagal maneuvers

Objective: Vagal maneuvers can cause a bradycardiac response with a reciprocal increase in parasympathetic outflow and reduction of sympathetic tone. Heart rate variability (HRV) analysis is useful in the evaluation of the autonomic nervous system. The present study investigated the magnitude of heart rate (HR) reduction and autonomic response in healthy young adults following three vagal maneuvers: carotid sinus massage (CSM), the cold face test (CFT), and the Valsalva maneuver (VM). Materials and Methods: A prospective study was conducted in 50 healthy volunteers between 21 and 35 years old who completed CSM, the CFT, and the VM in random order. Before and after each test, the RR intervals were recorded by electrocardiography for 5 min to analyze variability in the time and frequency domains, and to monitor changes in the HR, blood pressure (BP), and body temperature (BT). Results: After each test, HR, BP, and BT significantly decreased compared with values at rest (all p values < 0.05). The mean HR during CSM, the CFT, and the VM significantly decreased by 4.0%, 3.2%, and 2.3%, respectively, revealing that CSM most potently induced HR reduction. Significantly increased variance of the RR (VAR) indicated that CSM, the CFT, and the VM induced cardiac autonomic function (p = 0.001, p = 0.009, and p = 0.009, respectively). Although not all of these changes were statistically significant, increased power of the normalized low-frequency component (LF%), decreased power of the normalized high-frequency component (HF%), and an increased LF/HF ratio suggested relative sympathetic enhancement. Only the VM had significant effects on sympathovagal balance in the LF%, HF%, and LF/HF (p = 0.006, p = 0.004, and p = 0.006, respectively). Conclusion: Of the three maneuvers, CSM had the greatest effects on HR reduction, while only the VM had significant effects on sympathovagal modulation. Although accurate assessment of vagal activity was not available from spectral analysis of HRV, the increases in VAR, LF%, and LF/HF, and decrease in HF% observed in this study suggest that increases in cardiac autonomic activities and sympathetic dominance occur as compensatory responses to HR reduction in a 5-min window following vagal maneuvers. More research is required to determine whether CSM is a superior initial nonpharmacologic treatment for supraventricular tachyarrhythmia in a young population if there are no contraindications. Copyright (C) 2011, Buddhist Compassion Relief Tzu Chi Foundation. Published by Elsevier Taiwan LLC. All rights reserved.