Non-invasive autonomic evaluation of cardiovascular parameters has used Fast Fourier transform (FFT) to evaluate low (LF) and high frequencies (HF) as index of sympathetic and parasympathetic activities respectively. FFT cannot be applied to brief transient phenomena, such as those observed on autonomic tests where acute changes of cardiorespiratory signals represent the first and most important stage of the autonomic performance towards homeostasis.

We have developed a Wigner-Ville (W-V) time-domain analysis to complement usual methods of evaluation in which information is taken only from frequency domain. W-V allows time visualization of the contribution of LF and HF to the observed changes of a signal.

We have evaluated RR intervals (RRI), systolic and diastolic blood pressure changes during a classical autonomic test: the Deep Breathing (DB). Continuous monitoring of ECG, blood pressure and respiratory flow was performed in 10 healthy subjects. LF and HF were calculated with FFT and W-V analysis in a 10 seconds single respiration. DB test elicited the typical respiratory modulation of systolic, diastolic (222 and 143 mmHg respectively) and cardiac rate (352 bpm). W-V analysis of RRI, systolic and diastolic signals showed that the parasympathetic band is increased (p<0,01 in all cases) and shifted to the frequency range of the LF band with a significant increase of amplitude (p< 0,01 in all cases)

In summary, when compared with FFT, W-V analysis allows evaluation of autonomic variability during short non-stationary periods and may constitute a useful advance in the assessment of autonomic function in both physiological and pathological conditions.