(A) Hypertension from vasopressor boluses (phenylephrine and vasopressin) transiently increased the blood flow. (B) Hypotension from vasodilator boluses (nitroprusside) caused a transient decrease in blood flow. (C) Withholding ventilation causing hypoxia and hypercarbia resulted in increased blood flow. In all three cases, the x-axis represents time in minutes and the y-axis represents the percentage of change in the blood flow index. MAP = mean arterial pressure.