Impact of smoking status on autonomic functions assessed by spectral analysis of heart rate variability

Abstract

Background and Aim: Increased sympathetic activity associated with cigarette smoking has been recognized as a major independent risk factor for cardiac morbidity and mortality. This study was aimed to assess and to differentiate cardiac autonomic activity by analysis of heart rate variability (HRV) in apparently healthy male regular light, moderate and heavy cigarette smokers. Methods: This comparative analytical study conducted in apparently healthy male regular cigarette smokers with age between 20 to 55 years. They were divided into light, moderate and heavy smokers (n=40 in each group) according to the cumulative effect of smoking calculated by pack‑years. For comparison, 70 apparently healthy male non‑smoker subjects were studied as control. HRV data was recorded in a controlled laboratory environment by a multichannel polyrite. Statistical analysis of data among the groups was performed by one‑way Analysis of variance (ANOVA). Association of different variables with a ratio of low‑frequency to high‑frequency power (LF‑HF ratio) was done by Pearson correlation and multivariate regression analysis was used to assess the independent contribution of smoking status to LF‑HF ratio. Results: Resting heart rate (HR) (P < 0.001), systolic blood pressure (P < 0.01), diastolic blood pressure (DBP) (I < 0.001) and rate pressure product (RPP) were found to be significantly high in all groups of smokers. Low frequency (LF) component, LF power expressed in normalized unit (LFnu) and LF‑HF ratio were significantly (P < 0.001) higher in all smokers than non‑smokers and were also significantly high (P < 0.05) in heavy smokers compared to light smokers. Total power, high frequency (HF) component and HF power expressed in normalized unit (HFnu) were found significantly (P < 0.001) less in all smokers compared to control and were also significantly (P < 0.05) low in heavy smokers compared to light smokers. HR and RPP in moderate smokers and DBP in light smokers showed a significant correlation with LF/HF ratio. LF/HF ratio showed significant and independent contribution to RPP in moderate smokers. Conclusion: Results of this study suggest cardiac autonomic dysfunction characterized by increased sympathetic activity with attenuated cardiac vagal modulation and shift of sympathovagal balance towards strong sympathetic dominance in regular cigarette smokers, that are more prominent in heavy smokers. Significant dose‑response association between cumulative smoking exposure, deranged cardiac autonomic function and increased cardiovascular stress were found in smokers.