In this study we propose a method to continuously assess the changes of spontaneous baroreflex sensitivity (BRS). Systolic arterial pressure and RR intervals are analyzed by time-frequency analysis to estimate their instantaneous powers as well as the time-course of their spectral coherence. The BRS estimated in classical frequency bands is compared to the BRS estimated in dynamic frequency bands centered on respiratory frequency. The possibility of obtaining reliable estimations of the BRS using the pulse interval from the pressure signal as a surrogate of the RR is considered. Results on a tilt table test database suggest that is possible to obtain reliable BRS estimates just from the analysis of the pressure signal, without the need of ECG recordings.