Observations on the avian pulmonary and bronchial circulation using labelled microspheres.

Domestic fowl, ducks, geese, Guinea-fowl, quail and pigeons were anaesthetised with intravenous pentabarbitone sodium. Carbonised microspheres (40,000-60,000), 15 micrometer +/- 5 micrometer in diameter and labelled with 85Sr (3M Company) were injected into the cannulated right atrium. After spontaneous breathing of room air the birds were killed and the radioactivity measured in the spleen, kidneys, brain, lungs and extrapulmonary primary bronchi. Small pieces of lung tissue were removed from the beginning (costal region), middle (costovertebral region), and the end (vertebral region) of the paleopulmonic parabronchi, in the direction of air flow. Microspheres found in samples of parabronchial tissue indicated the relative perfusion rates of the three regions. Thermal panting was induced in six domestic fowl and six pigeons, followed by injection of microspheres. No arteriovenous anastomoses were found to exist across the pulmonary bed in any of the species examined at rest or in the panting domestic fowl and pigeons. The extrapulmonary primary bronchus was found to be well perfused from the pulmonary artery in the domestic fowl and to a lesser extent in the other species. The perfusion of the parabronchi in the domestic fowl and pigeons at rest decreased in the direction of ventilatory gas flow. This blood flow gradient was significantly increased during thermal panting in the domestic fowl, but not in the pigeon.