Effects of Breathing Carbon Dioxide upon the Pulmonary Circulation

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Abstract
The effects of inhaling 5 per cent carbon dioxide in air on the pulmonary arterial blood pressure and flow were studied in 5 subjects with normal pulmonary circulations and in 10 patients with chronic pulmonary emphysema. In the 5 control subjects, with an average increase in arterial PCOCO2 of 6 mm. Hg (37 to 43) and a 3-fold increase in minute ventilation, both pulmonary arterial blood pressure and flow remained unchanged. In the 10 patients with chronic pulmonary emphysema with a similar increase in arterial PCOCO2 (45 to 52) and a 2-fold increase in minute ventilation, there was a 14 per cent increase in cardiac output and a rise in pulmonary arterial mean pressure of 4 mm. Hg. In these patients an increment in pulmonary arterial pressure was invariably associated with an appreciable increment in blood flow. The present study affords no support for the view that the breathing of air enriched with carbon dioxide elicits pulmonary vasoconstriction in either normal subjects or in patients with chronic pulmonary disease.