ObjectiveTo characterize the dose-related effects of dobutamine on pulmonary vascular tone and associated changes in right ventricular afterload in canine microembolic lung injury.DesignProspective, interventional study.SettingUniversity laboratory.SubjectsTen anesthetized and ventilated dogs.InterventionsRight heart catheterization for the measurement of pulmonary vascular resistance by multipoint mean pulmonary artery pressure (Ppa)/cardiac output (Q) plots, partitioning of pulmonary vascular resistance by the occlusion method, and determination of pulmonary arterial input impedance from spectral analysis of Ppa and Q waves, in ten anesthetized and ventilated dogs, before and after induction of acute microembolic lung injury, and without or with 5, 10, 15, and 20 &mgr;g·kg−1·min−1dobutamine.Measurements and Main ResultsMicroembolic pulmonary hypertension was associated with a shift of Ppa/Q plots to higher pressures, a slight decrease in the arterial component of pulmonary vascular resistance, a decrease in characteristic impedance, and an increase in the pulsatile component of right ventricular hydraulic load. At baseline, dobutamine had no effect on Ppa/Q plots at 5 and 10 &mgr;g·kg−1·min−1but increased Ppa at 15 and 20 &mgr;g·kg−1·min−1. In microembolic pulmonary hypertension, the only effect of dobutamine on Ppa/Q plots was a decrease in Ppa at 20 &mgr;g·kg−1·min−1. Dobutamine had no effect on the partitioning of pulmonary vascular resistance or on pulmonary arterial input impedance spectrum.ConclusionsDobutamine at doses up to 10 &mgr;g·kg−1·min−1has no flow-independent effect on the normal or the acutely hypertensive pulmonary circulation. Higher doses may be constricting or dilating depending on preexisting tone.