Contributions of bicarbonate ion and of dissolved CO2 to expired CO2 in dogs

Abstract

The indicator-dilution technique has been applied to the heart-lung system of anesthetized dogs with injection of test solutions into the right ventricle or pulmonary artery, collection of some thirty anaerobic blood samples over a period of 1 minute from a carotid artery, and collection of expired gases. The test solution contained a reference substance (Na22 or T-1824), labeled water, and C-13- or C-14-labeled HCO3– or dissolved CO2. Under control conditions, losses of the carbon isotopes from the blood stream and recoveries in the expired air indicated equilibration of CO2 amongst its several forms in the time of transit from the site of injection to the alveoli. After administration of acetazoleamide in dosages of 100 down to 20 mg/kg, fractional losses of labeled dissolved carbon dioxide increased by a factor of 4. Confirmatory results were obtained in experiments on the incorporation of O18 from H2O18 into expired CO2. It is concluded that, after inhibition of carbonic anhydrase, peripheral arterial blood differs in composition from end-alveolar capillary blood.