Wavelet decomposition of heart period data

Autonomic control over the cardiac cycle is mediated by the dynamic influences from the vagal and sympathetic nerves. Each division controlled in a non-linear fashion. To investigate the influence of vagal stimulation on the cardiac cycle, the authors used the wavelet transform (WT) to distinguish the frequency content of the heart period variability (HPV) data collected from standard 3 lead ECG. This method enabled them to show time series representation of the frequency content, which is not possible with a standard discrete Fourier transform or a Short Time Fourier Analysis. By characterizing the heart period during vagal nerve stimulation (VNS), it may be possible to identify the dynamic relationship between vagal output and control over variability in the cardiac cycle. To test the effects of the left vagal nerve stimulation modulation of the heart period (HP), the WT was conducted on data collected before and during stimulation of the left vagus nerve. The authors' results show that WT reveal a decrease in low frequency variability. They feel that the WT is a valuable tool to estimate instantaneous frequency changes in HPV during dynamic events.