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

¹ Departments of Physiological Chemistry and Medicine, the Johns Hopkins School of Medicine and the Medical Division, Baltimore City Hospitals, Baltimore, Maryland

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.

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