Exchange of Blood Between Pulmonary and Systemic Circulations via Bronchopulmonary Anastomoses

In anesthetized dogs, the dye-dilution technique was applied to detect the transfer of blood between the bronchial and pulmonary vessels. The injection of Cardio-green into the pulmonary artery did not show a double peak in the dye-concentration curve of blood in the azygos vein. This does not exclude the possibility of a shunt from the pulmonary artery to the bronchial veins because the flow of the dye may take longer to reach the bronchial veins than does that from the bronchial artery. The injection of the dye into the left ventricle with sampling of the blood in the left atrium showed a double peak in the dyedilution curve. The latter is interpreted to indicate blood flow from the bronchial arteries to the pulmonary vessels via the bronchopulmonary anastomoses. In five dogs, the mean value for bronchopulmonary flow was 8 per cent of left ventricular output. The corresponding flow values were increased in three dogs with chronic ligation of the left pulmonary artery, not increased in four dogs with pulmonary embolization, and reduced in two dogs subjected to inhalation of heat. All these results suggest that previous estimates of 1 per cent for bronchial flow may be an underestimation, but the maximum value of 8 per cent in anesthetized dogs calculated by the dye-dilution technique will have to be reevaluated by other methods.