Fig. 2. Signal-averaged impedance cardiograms during infusion epinephrine, esmolol, nitroprusside, and norepinephrine as compared with the two placebo periods (A and B). Averaging was done with respect to interbeat interval length. Independent of interbeat interval length, epinephrine infusion caused a higher and earlier ejection component as compared with placebo; esmolol had the opposite effect.