Multivariate time-variant identification of cardiovascular variability signals: a beat-to-beat spectral parameter estimation in vasovagal syncope. - Luca T. Mainardi; Anna M. Bianchi; Raffaello Furlan; Simona Piazza; Riccardo Barbieri; Valerio di Virgilio; Alberto Malliani; Sergio Cerutti (IEEE Trans. Biomed. Eng., 1997)