Case StudiesMorlet wavelet transforms of heart rate variability for autonomic nervous system activity

•Morlet wavelet transforms may be used to evaluate the cardiac autonomic regulation.•Morlet heart rate variability indices detect cardiac sympathetic inhibition.•Normalized Morlet can compare oscillations of the same signal at different times.•Normalized Morlet wavelet can compare oscillations between two different signals.

The aim of this study was to characterize the cardiac autonomic nervous system (ANS) through Morlet wavelet transforms of heart rate variability (HRV) and compare to Fast Fourier Transform (FFT) analysis. Cardiac sympathetic and parasympathetic blockades were studied in conscious rats. Morlet and FFT were performed in (1) high-frequency band (HF: 0.6 to 3 Hz), (2) mid-frequency band (MF: 0.3 to 0.6 Hz), and (3) low-frequency band (LF: 0.07 to 0.3 Hz). While cardiac sympathetic inhibition with metoprolol did not alter average HR, Morlet normalized power indices were able to detect it with the highest level of significance in LF. FFT HRV indices detected only parasympathetic blockade effects in LF and MF of the HRV, which accompanied the increase in the average HR. Thus, alterations of cardiac ANS may be sensitively detected through Morlet wavelet of HRV while average HR is not altered.