THE DRAGONS BREATH - A MODEL FOR THE DYNAMICS OF BREATHING AND FAVEOLAR VENTILATION IN AGAMID LIZARDS

The lungs of the dragon lizards Ctenophorus nuchalis and Pogona vittic eps are unicameral. We have used the scanning electron microscope (SEM ), X-ray, and computerized tomography (CT) scans to study the static a nd dynamic behavior of the lung during the respiratory cycle in both a naesthetized and unanaesthetized, awake lizards. One awake, quite C. n uchalis at 37 C held 0.18 ml of air/g body mass in its lungs during no nventilatory periods. However, the right lung holds a smaller volume t han the left. During ventilation the caudal third of the lung retains a relatively constant volume, while the anterior portion of the lung u ndergoes the major changes in volume. Over 70% of the faveoli are loca ted in the anterior two-thirds of the lung. CT scans of P. vitticeps r eveal that the dorsal faveoli represent a larger (thicker) band than t he ventral faveoli. The ventral surface is also considerably compresse d and distorted by other abdominal organs. Most of the pulmonary arter ies are located on the dorsal and lateral external walls of the lung. We propose that air moves into the faveoli during inspiration, as the body wall moves outwards, pulling with it the external wall of the lun g which is attached by strong connective tissue. If the trabecular net work maintains a relatively constant shape, the faveoli will be pulled open and air will be sucked into them. As the lung deflates, the fave oli are compressed against the relatively rigid trabecular network and air is forced out. Hence, each faveolus acts as a bellows. Movement o f air in the lung and the function of pulmonary surfactant are also di scussed.