Cigarette smoking and heart rate variability: Dynamic influence of parasympathetic and sympathetic maneuvers

Background: Cigarette smoking has been associated with increased activity of the sympathetic nervous system. In this study, we investigated cardiac autonomic function in heavy smokers and nonsmoker controls by analysis of heart rate variability (HRV). Method: Twenty-four long-term heavy smokers (men) and twenty-two nonsmoker subjects (hospital staff) were included to study. Time domain [mean R-R interval (RR), the standard deviation of R-R interval index (SDNN), and the root mean square of successive R-R interval differences (RMSSD)] and frequency domain [high frequency (HF) low frequency (LF), and LF/HF ratio] parameters of HRV were obtained from all participants after 15 minutes resting period in supine position (S), during controlled respiration (CR), and handgrip exercise (HGE) over 5-minute periods. Results: Baseline SDNN and RMSSD values were found to be lower in smokers than in nonsmokers. (64 10 vs 78 22, P < 0.05 and 35 12 vs 54 30 ms, P < 0.05). Baseline LF/HF ratio was also found to be higher in smokers than in nonsmokers (1.3 +/- 0.6 vs 0.9 +/- 0.5 ms, P < 0.05). The other HRV parameters including R-R interval, LF, and HF were not significantly different. During CR, expected increase in RR, SDNN, and RMSSD did not occur in smokers, while it did occur in nonsmokers. Most HRV indices were significantly affected by HGE in both groups. In addition, the duration of smoking was found to be inversely correlated with RMSSD and HF and positively correlated with LF/HF ratio. Conclusion: Vagal modulation of the heart is blunted in heavy smokers, particularly during a parasympathetic maneuver. Blunted autonomic control of the heart may partly be associated with adverse event attributed to cigarette smoking.