Abstract
Background: Various studies using heart rate variability (HRV) as a tool have found reduced HRV in smokers in comparison with non-smokers. However, not many studies have studied the influence of smoking on HRV in light and heavy smokers calculated by pack years.

Aim and Objective: The main aim of this study was to measure and compare the influence of smoking on autonomic functions in male light and heavy cigarette smokers using HRV.

Materials and Methods: The present was conducted in the Department of Physiology, Navodaya Medical College, Raichur. Permission to conduct the study was obtained from the Institutional research ethical committee. This study was conducted among male cigarette smokers with age between 20 and 50 years who were apparently healthy. The selection of subjects participating in the study was done by simple random sampling, the subjects were residents of the Raichur district. The study group subjects were divided into light and heavy smokers considering both the amount and duration of smoking calculated by pack years. HRV was recorded by using the instrument Polygraph (AD instruments, Australia, model noML870). Statistical analysis was done by independent sample t-test to compare between the groups using EPI Info Version 7.0 software. A P < 0.05 was considered as statistically significant whereas a P < 0.001 was considered as highly significant.

Results: The HRV parameters indicating sympathetic function such as low frequency (LF) component, LF power expressed in normalized unit (LFnu) and LF-HF ratio were significantly increased in heavy smokers in comparison to light smokers, whereas the HRV parameters indicating parasympathetic function such as total power, high frequency (HF) component and HF power expressed in normalized unit (HFnu) were significantly decreased in heavy smokers in comparison to light smokers.

Conclusion: Increased sympathetic stimulation associated with a decrease in the cardiac vagal modulation leading to imbalance in the autonomic functions was more in heavy smokers when compared to light smokers.