Pulmonary arteriovenous anastomoses in the avian lung: do they exist?

A search for pulmonary arteriovenous anastomoses was made in 15 adult domestic fowls using Lycopodium spores and microspheres. The diameter of the spores and microspheres ranged from about 10 to 33 mum. To dilate any pulmonary arteriovenous anastomoses, the birds were warmed to induce panting, killed with chloroform, or injected intravenously with papavarine. The spores or microspheres were injected either into the jugular vein under anaesthesia, or into the pulmonary artery after death. After the pulmonary arterial injections, the effluent from the pulmonary vein, and histological sections of the lungs, were examined for spores or microspheres. When injections were made into the jugular vein, blood smears from the pulmonary veins, left atrium, and the aorta, as well as histological sections of the lungs and other organs were inspected. The results of all these experiments showed that no spores or microspheres were ever found on the venous side of the pulmonary circulation, indicating absence of pulmonary arteriovenous anastomoses.