Effect of atrial septal defects on hemodynamic alterations caused by acute partial obstruction of pulmonary artery.

P investigations of the hemodynamic effects of progressive constriction of the pulmonary artery have demonstrated the basic principles of right ventricular compensation for an increase in resistance to outflow." Acute obstruction of the pulmonary artery results initially in an increase in right ventricular diastolic volume and in increased vigor of cardiac contraction, with maintenance of cardiac output and systemic blood pressure. The right ventricular systolic pressure is moderately increased. With increasing degrees of pulmonary obstruction, the right ventricle becomes distended, resulting in a heightened diastolic pressure and further increase in right ventricular systolic pressure. Cardiac output and systemic blood pressures are maintained or slightly reduced. Finally, with even greater degrees of obstruction, one sees pronounced distention of the right ventricle associated with further elevation in diastolic pressure, a great reduction in cardiac output, and a decrease in systemic blood pressure.