Fig. 7. Effect of blood flow on the dose requirements of intracarotid propofol. Intraarterial verapamil is a potent cerebral vasodilator. (  A ) The dose of intracarotid propofol required to produce 10 min of electrocerebral (electroencephalographic [EEG]) silence significantly increases with verapamil pretreatment (n = 14,  P = 0.004). (  B ) The dose requirement of propofol is linearly related to the increase in blood flow after verapamil pretreatment (  r = 0.75,  P = 0.0021). (  C ) Increase in cerebral blood flow with changes in ventilation directly affects the dose of propofol required for electrocerebral silence. HYO = hypocapnia; HYR = hypercapnia; NOR = normocapnia. Adapted from Joshi  et al. 33