Spectral analysis of Heart Rate Variability (HRV) can be used for the assessment of cardiovascular autonomic control. In this study Smoothed-Pseudo Wigner-Ville Distribution (SPWVD) has been used to evaluate the effect of local anesthesia on HRV parameters in a group of fourteen patients undergoing brachial plexus block (local anesthesia) using the transarterial technique. Instead of using the fixed boundaries of the LF (0.04-0.15 Hz) and the HF (0.15-0.4 Hz) components, the center frequency and the standard deviation spectral extension was used to estimate the boundaries related to the two components of the HRV signal. The boundaries related to the HF component of the signal were estimated using the cross-spectrum between the HRV signal and the respiration signal. The LF component boundaries were estimated directly from the time-frequency representation of the HRV signal. The statistical analysis showed that the (LF)/HF amplitude ratio decreased within an hour of the application of the brachial plexus block compared to the values at the start of the procedure. These changes were observed in eleven of the fourteen patients included in this study.