INDEPENDENT AND SIMULTANEOUS UNILATERAL OCCLUSION OF THE PULMONARY-ARTERY AND EXTRA-PULMONARY PRIMARY BRONCHUS IN BROILERS

Acutely tightening a snare around one pulmonary artery previously was shown to trigger a reversible ventilation-perfusion (V/Q) mismatch in broilers, as reflected by decreases in the partial pressure of oxygen in arterial blood (hypoxemia), accompanied by increases in the hydroge n ion concentration (acidosis) and partial pressure of carbon dioxide (hypercapnia). In the present study, snares were loosely implanted aro und the right pulmonary artery and the right extrapulmonary primary br onchus in anesthetized male broilers. These snares were tightened and released independently and then simultaneously to evaluate the possibi lity that directing the entire respiratory minute volume toward the le ft lung might attenuate the V/Q mismatch caused by forcing the entire cardiac output (CO) through the left lung. Fully reversible arterial b lood hypoxemia, acidosis, and hypercapnia occurred when either snare w as tightened independently. Presumably, tightening the bronchial snare restricted ventilation but not blood flow to the right lung, thereby permitting blood to perfuse poorly ventilated gas exchange surfaces. S imultaneously tightening both snares triggered arterial blood hypoxemi a, acidosis, and hypercapnia similar to or greater in magnitude than t he responses obtained by tightening the pulmonary artery snare indepen dently Tightening either snare independently or both snares simultaneo usly caused pulmonary arterial pressure to increase (pulmonary hyperte nsion), and permanent obstruction of one bronchus in a separate experi ment caused an increase in the right:total ventricular weight ratio, w hich is indicative of chronic pulmonary hypertension. The mean systemi c arterial pressure decreased when the pulmonary artery snare was tigh tened independently or in combination with the bronchial snare, but no t when the bronchial snare was tightened independently. The respirator y rate increased and the heart rate decreased when the pulmonary arter y snare was tightened independently, but not when the bronchial snare was tightened independently or in combination with the pulmonary arter y snare. These results demonstrate that the V/Q mismatch caused by for cing all the CO to perfuse one lung cannot be attenuated by simultaneo usly directing the entire respiratory minute volume toward the same lu ng.