title: Hemodynamic effects of vasodilator agents in dogs with experimental ventricular septal defects.
abstract: The ratio of pulmonary to systemic vascular resistance (Rp/Rs) largely determines the amount of left-to-right shunting and pulmonary to systemic flow rat (Qp/Qs) in the presence of a large isolated ventricular septal defect. The possibility that pharmacologic reduction of systemic vascular resistance with alpha-adrenergic receptor blockade or beta-adrenergic receptor stimulation would increase the ratio Rp/Rs, and therefore reduce the ratio Qp/Qs, was studied in dogs in which ventricular septal defects had been surgically created. Administration of phentolamine and phenoxybenzamine caused a 42% reduction in Rs and no reduction in Rp. Qs was unchanged and Qp declined by 24% and the ratio Qp/Qs fell by 32%. Infusion of the beta-adrenergic receptor stimulant isoproterenol also reduced Qp/Qs. However, this was accomplished as a result of an increase in Qs and at the expense of an increase in heart rate. As a decline in the ratio Qp/Qs has been shown to be beneficial to patients with large left-to-right shunts, pharmacologic reduction of systemic vascular resistance may prove to be helpful in treating congestive heart failure in those patients with large left-to-right shunts at the ventricular level who are refractory to the usual decongestive measures.
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D006345:Heart Septal Defects, Ventricular / Q000188:drug therapy*; D006439:Hemodynamics / Q000187:drug effects*; D007545:Isoproterenol / Q000627:therapeutic use; D010643:Phenoxybenzamine / Q000627:therapeutic use; D010646:Phentolamine / Q000627:therapeutic use; D011652:Pulmonary Circulation / Q000187:drug effects; D014655:Vascular Resistance / Q000187:drug effects; D014665:Vasodilator Agents / Q000627:therapeutic use*
chemical_list: D014665:Vasodilator Agents; D010643:Phenoxybenzamine; D007545:Isoproterenol; D010646:Phentolamine