Gas Exchange after Pulmonary Thromboembolization in Dogs

Gas exchange following experimental pulmonary thromboembolization was studied with an inert gas elimination technique in 17 dogs. Pulmonary arterial, systemic arterial, and expired gas concentrations of six gases infused intravenously were measured before embolization and 5,10,15,30,60, and 120 minutes after embolization. Distributions of ventilation-perfusion (VA/Q) ratios were derived from the measured concentrations. In all dogs, embolization caused an increase in blood flow and ventilation to VA/Q ratios less than 1. There were no lung units with VA/Q ratios between 10 and 100 before embolization, but, in two-thirds of the dogs, such regions developed after embolization. Ventilation to unperfused lung showed a transient increase of 2-6%. Radioisotope studies of lobes removed post-mortem indicated that thromboemboli rarely caused complete abolition of lobar blood flow. Pulmonary embolization did not cause arteriovenous shunts to appear. The hypoxemia caused by embolization could be accounted for by the changes in VA/Q distributions. Over the 2-hour period after embolization, lung function improved as the distributions partially returned toward the preembolization patterns.