Fractal Scaling of Heart Rate Variability in Young Habitual Smokers


Abstract: The effect of cigarette smoking on the fractal organisation of the heartbeat regulating system was investigated by power spectral analysis. The heart rate variability (HRV) signal was obtained from the consecutive RR intervals of ECG. Power law behaviour of 1/f\beta type was studied to assess the fractal organisation of the heartbeat. Changes in the ratio of low frequency (PLF) to high frequency power (PHF) were used to assess the state of sympathovagal balance. The following statistical procedures were employed, as appropriate: Student's t-test for unpaired samples to compare mean values and paired t-test to compare changes within groups, and linear regression analysis. Experimental data were reported as means±SD. The differences between mean values were considered significant for p<0.05. In young smokers, the slope of the 1/f\beta relationship was significantly steeper than in non-smokers. The spectral exponent (\beta) increased during standing in non-smokers but there was no significant change in smokers. Standing also induced a significant increase in the P_LF/P_HF ratio in the non-smokers but no significant change was observed in smokers. These results suggest that smoking induces alteration in the fractal behaviour of HRV and disrupts the regulatory mechanisms, which show complex fluctuations and long range power-law correlations of the heartbeat recorded in non-smoking subjects. This alteration may contribute to the higher risk of cardiovascular diseases.

Keywords: Heart rate, fractal scaling, smoking, postural change

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