Effects of acute smoking on heart rate variability in students

Abstract

Cigarette smoking is a major cause of preventable morbidity and mortality in the world. There is altered autonomic activity in smokers which also predisposes to cardiovascular morbidity and mortality. To monitor the autonomic activity, heart rate variability has emerged as efficient tool. This study attempted to clarify the acute effects of cigarette smoking on autonomic nervous function among smokers. Twenty one light smokers (smoking less than 10 cigarettes a day) with a mean age of 22.36±0.16 years take part in the study (52% men, 48% women). They were studied in the morning hours in a quiet room at a comfortable temperature. Time domain (SDNN, RMSSD, pNN50), frequency domain (TP, HF, VLF, LF and LF/HF ratio) and nonlinear (SD1, SD2, ApEn, SampEn, D2, DFA1, DFA2) parameters of HRV were obtained from all participants for 10 minutes before and 10 minutes after smoking a cigarette while subjects were resting in a supine position and. Statistical analysis was performed using Mann‐Whitney test. There were no significant differences in heart rate during non‐smoking and smoking period (70.75±2.30 vs 73.37±2.33 beat/min, p=0.217). Time domain parameters were found to be lower during smoking period than that during non‐smoking period (SDNN: 38.07±3.91 vs 50.53±5.64 ms, p=0.001; RMSSD: 39.39±4.87 vs 56.4±7.57 ms, p=0.001 and pNN50: 17.08±3.61 vs 28.63±4.28 %, p=0.002). Frequency domain measures were also significantly lower during smoking period than that during non‐smoking period (TP: 1578.31±387.76 vs 2975.75±788.91 ms2, p=0.001; VLF: 52.52±10.11 vs 108.96±24.56 ms2, p=0.008; LF: 719.5±130.54 vs 1210.54±262.29 ms2, p=0.013 and HF: 804.96±275.86 vs 1650.12±578.23 ms2, p=0.0009). Nonlinear measures were significantly lower during smoking period than that during non‐smoking period (SD1: 27.88±3.45 vs 39.92±5.36 ms, p=0.001; SD2: 45.79±4.45 vs 58.84±6.5 ms, p=0.003; D2: 1.83±0.36 vs 3.09±0.37, p=0.013). The other HRV parameters including LF/HF ratio, pLF, pHF, ApEn, SampEn, DFA1, DFA2 were not significantly different. These results suggest that acute smoking has been associated with increased activity of the sympathetic nervous system and decrease in vagal cardiac control.