Ventilation and gas exchange in the Carpet Python,Morelia spilotes variegata

Abstract

The structure, dimensions and gas exchanging properties of the lungs of the Australian Carpet PythonMorelia spilotes variegata have been studied by dissection, by sampling lung gas and pulmonary venous blood and by using radioactive techniques to monitor distribution of ventilation (\(\dot V\)) and blood flow (\(\dot Q\)). The lungs have alveolar and saccular parts (mean capacities 10.2 and 129.3 ml/kg body weight, respectively). The sacs store inspired air creating a “flow through” situation which abolishes the dead space effect, prevents large expansions of the alveolar lung and allows gas exchange during both inspiration and expiration. Gas exchange was measured in intubated snakes in the resting and active states at 20–26 °C. In the resting state, respiratory frequency, tidal volume and ventilation were 1.72±0.56/min, 14.8±10.8 ml/kg, 22.04±7.75 ml/kg · min and pulmonary venousPO2,PCO2 and pH were 58.9±14.5 Torr, 21.5±4.2 Torr, and 7.55±0.07 Torr, respectively. R. Q. was low, 0.65±0.11. In the active state both ventilation (\(\dot V\)) and cardiac output increase and blood flow is redistributed more evenly along the alveolar lung, enabling increased O2 uptake. Since blood flow (\(\dot Q\)) in the alveolar lung is stratified (Read and Donnelly, 1972) redistribution of\(\dot Q\) during activity is proposed as a possible reserve capacity for O2 extraction by reptilian lungs.