Passive body movement and gas exchange in the frilled lizard (Chlamydosaurus kingii) and goanna (Varanus gouldii)

Abstract

The saccular lung in lizards is large and highly compliant compared with mammalian lungs, and these properties led us to question to what extent body movements could affect pulmonary gas exchange and the partial pressure of arterial blood gases. Specimens of two species of lizards, the frilled lizard (Chlamydosaurus kingii, approximately 600g body mass) and the goanna (Varanus gouldii, approximately 1400 mass), were anaesthetised, maintained at approximately 36 °C and mechanically hyperventilated to lower the arterial partial pressure of carbon dioxide (Pa(CO2)) to below apnoeic threshold. Respiratory system compliance (C(rs)) averaged O.112mlkg-1pa-1 (goanna) and 0.173mlkg-1pa-1 (frilled lizard), which is approximately 7-11 times the predicted value for a mammal of similar body mass. Mechanical ventilation was interrupted, and the changes in Pa(CO2) and Pa(O2) were monitored over the following 10 min as the animal was either left immobile or subjected to imposed lateral body movements. During the post-hyperventilation apnoea, Pa(CO2) increased whereas Pa(O2) did not always fall, sometimes even increasing, suggesting a reduction in the importance of pulmonary shunts. No significant differences were detected in the time course of changes in arterial blood gas levels or heart rate between runs with or without body movement. We conclude that in these species of lizards, despite the high C(rs), lateral chest wall movements neither hinder nor favour pulmonary gas exchange.