Figure 2. Time course of heart rate, arterial pressure, and respiratory rate with a 40 degree head-up tilt before and during cardiac sympathetic blockade by epidural anesthesia. Mean plus/minus SD from 10 awake subjects. Time of epidural injection of bupivacaine is indicated by the full vertical line. Tilt with the sympathetic system intact (open symbols) induced a significant increase in heart rate and a slight decrease in arterial pressure. During cardiac sympathetic blockade (closed symbols), the increase in heart rate evoked by tilt was significantly attenuated. Respiratory rate remained unchanged throughout the study period. * P < 0.05.