The phenomenon of respiratory sinus arrhythmia causes a difference in milliseconds between consecutive R waves of the ECG. These time variations are plotted obtaining a tachogram, which is then analysed through the spectral analysis of fast wavelet transformation. This allows filtration of the high frequencies (HF) of the tachogram, related only to parasympathetic activity, which are then passed through fast wavelet transformation again, but this time in reverse. From this new analysis the respiratory pattern is obtained. This represents the percentage of HF from the total activity of the autonomic nervous system which is demonstrated as the ANI value (0 – 100).