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Quadratic time-frequency (TF) distributions have an excellent joint TF resolution, but their applicability is limited by the presence of interferences. In this communication, a methodology for robustly estimating TF coherence (TFC), based on signal-dependent smoothing of the Wigner Ville distribution, is shown to provide a reliable continuous quantification of cardiovascular interactions during non stationary conditions. Bias, standard deviation and tracking capability of the TFC estimator have been quantified in different physiological contexts. Linear coupling between HRV and SPV during tilting has been assessed. It is observed that orthostatic stress provokes a significant increase (p ¿¿0.02) of TFC in both LF and HF range.