EFFECTS OF A CHRONIC AORTOPULMONARY SHUNT ON PULMONARY HEMODYNAMICS IN PIGLETS

Systemic-to-pulmonary shunting in growing pigs has been proposed as an experimental model of high-flow pulmonary hypertension associated with congenital heart defects. We investigated multipoint pulmonary arterial pressure (Ppa) vs. cardiac output (and) plots and pulmonary vascular impedance spectra in 13 piglets aged similar to 4 mo and ventilated alternatively in hyperoxia (inspired O-2 fraction 0.4) and in hypoxia (inspired O-2 fraction 0.12). The measurements were done 8 wk after either an anastomosis between the thoracic aorta and the pulmonary trunk (n = 7 piglets) or a sham operation (n = 6). Cardiac output was altered by a manipulation of venous return. In the sham-operated piglets, hypoxia increased Ppa by an average of 12 mmHg over the entire range e of and studied, from 60 to 120 ml/kg, and increased both 0 Hz (Z(0)) and characteristic (Zc) pulmonary vascular impedance. In the shunted piglets compared with the sham-operated piglets in hyperoxia, Ppa was increased by an average of 5-6 mmHg at all levels of Q studied, from 60 to 120 ml/kg (P < 0.01), and Zc was also increased (P < 0.01), whereas Z(0) was unchanged. In the shunted piglets, hypoxia increased Ppa at all levels of Q studied only to an average of 3 mmHg, and neither Z(0) nor Zc was altered by hypoxia. We conclude that an aortopulmonary shunt of 2-mo duration in growing pigs increases both pulmonary vascular resistance and impedance and is associated with a blunting of pulmonary vascular reactivity to hypoxia.