Spectral Analysis in Time series

The effect of nicotine  is complex and most of the research of the heart rate variability is done with tobacco  in  participants  trying  to  cease  smoking.  Such  studies  are  limited  with  desensitization  of nicotinic  receptors, emergence of abstinence symptoms, and  the overall modified activation of  the autonomic nervous system.
The aim of this study is to show the effect of nicotine on young smokers and nonsmokers using descriptive and spectral analytical methods of the heart rate variability. The  research was conducted on 50 participants  (m=23,  f=27), average age of 21.8±1.49 years, who were divided  into nonsmokers  (n=26, m=11,  f=15) and  smokers  (n=24, m=12,  f=12). Smokers were
smoking 14.8±6 cigarettes on average for 4.77±2.19 years. A baseline ECG lasting 100s was recorded, followed by  chewing  a gum  containing 4 mg of nicotine,  after which  an ECG  lasting 100  s was  re-recorded.  The  ECG  analysis  was  followed  by  the  analysis  of  the  heart  rate  variability  using  time
domain and frequency domain methods. In order to show the effects of nicotine more precisely, the resulting  changes  (Δn)  were  calculated  as  the  difference  between  the  final  and  initial  values  of variables,  after which  the  changes  (Δn =  T2-T1) were  statistically  compared between  smokers  and
nonsmokers. After the application of nicotine, a significant difference was observed in the changes of the average
length of  the RR  intervals  (p=0.01) and  the heart  rate  (p<0.01) between  smokers and nonsmokers.
Within  the  spectral  analysis,  a  significant  difference was  observed  in  the  changes  of  the  absolute value  of  the  spectrum  of  low  frequencies  (LF,  p<0.05),  the  standardized  values  of  high  and  low frequency spectra (LF (n.u.), HF (n.u.), p<0.05) and the LF and HF ratio (LF/HF, p<0.05).
The  heart  rate  variability  analysis  proved  to  be  a  valuable  indirect  method  for  analyzing  the autonomic  nervous  system.  The  obtained  results  confirm  that  the  effect  of  nicotine  significantly affects  nonsmokers,  reducing  their  heart  rate  variability  and  the  parasympathetic  tone,  while increasing the heart rate and the sympathetic tone.

Keywords: Heart rate variability, autonomic nervous system, nicotine, spectral analysis, ECG

The Periodic Autoregressive Model Family Box & Jenkins - PAR(p) has been employed in the prediction of Affluent Natural Energy (ENA), an important variable in the energetic operation planning of hydroelectric systems. In order to increase the accuracy of the ENA’s predictions obtained by the PAR(p) model, we propose the application of Multi-Channel Singular Spectrum Analysis - MSSA in the simultaneous filtering of the ENA series of the four subsystems that comprise the National Interconnected System. The PAR(p) models are adjusted to the filtered time series and the resulting predictions are compared with those obtained by models PAR(p) adjusted to the original time series. The results presented in the paper show the effectiveness of filtering in improving the accuracy of ENA’s predictions obtained by the PAR(p) model.