Fig. 1. Concentration–response curves of halothane (n = 5) and enflurane (n = 5) on spontaneous sinus cycle duration (RR, ms) and on perfusion pressure (PP, mmHg). Halothane (open circles) induced a concentration-dependent increase in RR interval, whereas enflurane (filled circles) did not. The perfusion pressure decreased with both agents, without concentration-dependence. #  P < 0.001  versus baseline;‡  P < 0.01  versus baseline;†  P < 0.05  versus baseline;$  P < 0.05  versus 1%;*  P < 0.05  versus 3%.