OWERKOWICZ, T.; MUNNS, S.; HICKS, J.W.; Harvard University, Cambridge, MA; Univ. of California, Irvine; Univ. of California, Irvine: Function of the postpulmonary septum in lung ventilation in Varanus.
Monitor lizards (genus Varanus) are unique among the Squamates in possessing a postpulmonary septum (PPS). The PPS is a nonmuscular membrane, adhering closely to the caudoventral surface of the lungs. We hypothesised the PPS may be important in augmenting the tidal volume of costal inspiration (TVi). We measured gas exchange and ventilatory airflow during treadmill exercise in juvenile savannah monitors (V. exanthematicus) before and after surgical detachment of the PPS from the lungs. Since gular pumping is used by monitor lizards to inflate the lungs and may mask the effect of PPS detachment, we studied the effect of PPS removal in animals with and without the gular pump. Maximum rate of oxygen consumption (VO2max) was lower in experimental animals as compared to sham-operated controls, significantly so in animals without the gular pump. This was reflected in 25% reduction in locomotor endurance in experimental animals. Breath-by-breath analysis of the ventilatory trace showed TVi was significantly reduced in experimental animals when the gular pump was disabled – at 1.5 km/h, when animals reached VO2max, TVi averaged 63 ml/kg in controls, and 52 ml/kg in experimental animals. At 1.5 km/h, gular pumping (when functional) contributed a significantly greater proportion of minute ventilation in experimental animals (45%) than in controls (32%). The PPS appears to provide structural support to the caudal region of the heterogeneously partitioned lungs of monitor lizards. Without the PPS, the caudal lung regions cannot be fully inflated by costal means alone, which limits the animals’ aerobic performance. Whether the PPS plays other roles in venous return or lung perfusion remains to be investigated.
