Figure 7-11 Histograms depict the effects of sodium nitroprusside (SNP), halothane, and isoflurane on total arterial compliance (C, top), total arterial resistance (R, middle), and characteristic aortic impedance (Z_C , bottom). The low, medium, and high doses of volatile anesthetics are 1.25, 1.5, and 1.75 minimum alveolar concentrations (MACs), respectively. SNP doses produce comparable changes in mean arterial pressure. *, Significantly (P < .05) different from the control; †, significantly (P < .05) different from the low dose; §, significantly (P < .05) different from the middle dose; ‡, significantly (P < .05) different from halothane. (Adapted from Hettrick DA, Pagel PS, Warltier DC: Differential effects of isoflurane and halothane on aortic input impedance quantified using a three-element Windkessel model. Anesthesiology 83:361–373, 1995.)