Independent and simultaneous unilateral occlusion of the pulmonary artery and extra-pulmonary primary bronchus in...

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 hydrogen ion concentration (acidosis) and partial pressure of carbon dioxide (hypercapnia). In the present study, snares were loosely implanted around the right pulmonary artery and the right extrapulmonary primary bronchus in anesthetized male broilers. These snares were tightened and released independently and then simultaneously to evaluate the possibility that directing the entire respiratory minute volume toward the left lung might attenuate the V/Q mismatch caused by forcing the entire cardiac output (CO) through the left lung. Fully reversible arterial blood hypoxemia, acidosis, and hypercapnia occurred when either snare was 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. Simultaneously tightening both snares triggered arterial blood hypoxemia, acidosis, and hypercapnia similar to or greater in magnitude than the responses obtained by tightening the pulmonary artery snare independently. Tightening either snare independently or both snares simultaneously caused pulmonary arterial pressure to increase (pulmonary hypertension), and permanent obstruction of one bronchus in a separate experiment caused an increase in the right:total ventricular weight ratio, which is indicative of chronic pulmonary hypertension. The mean systemic arterial pressure decreased when the pulmonary artery snare was tightened independently or in combination with the bronchial snare, but not when the bronchial snare was tightened independently. The respiratory rate increased and the heart rate decreased when the pulmonary artery snare was tightened independently, but not when the bronchial snare was tightened independently or in combination with the pulmonary artery snare. These results demonstrate that the V/Q mismatch caused by forcing all the CO to perfuse one lung cannot be attenuated by simultaneously directing the entire respiratory minute volume toward the same lung.