PATHO-PHYSIOLOGY OF GAS-EXCHANGE AND PULMONARY PERFUSION IN PNEUMOCOCCAL LOBAR PNEUMONIA IN DOGS

An inoculum of Streptococcus pneumoniae type III was placed into a left lower lobe bronchus of 6 dogs (group P), and in 6 other dogs (group C) a sterile control inoculum was used. Measurements of shunt (Qs/Qt) and venous admixture (Qva/Qt) were made immediately before (day 1) and 48 h after (day 3 ) inoculation. All dogs in group P had extensive lobar pneumonia confirmed radiologically and at autopsy; group C had only small sterile lesions at the site of inoculation. In group P, mean Qs/Qt and Qva/Qt increased significantly to 0.15 and 0.21, respectively. Mean lobar Qs/Qt, calculated using blood samples from lobar veins at thoractomy on day 3, was markedly increased in the pneumonia lobe (0.69) compared with the contralateral lower lobe (0.08), and alveolar ventilation of that lobe approached zero. Perfusion of the infected lobe determined by radioactive microspheres showed a variable and statistically nonsignificant decrease between control and infected states that was not affected by O2 breathing. In group C there was no change between days 1 and 3 in gas exchange or in distribution of pulmonary perfusion. Hypoxemia in pneumonia was evidently due to both increased shunt and venous admixture in the infected regions and local hypoxic vasoconstriction was in most instances ineffective in directing blood flow away from the consolidated lobe.