Terrestrial locomotion does not constrain venous return in the American alligator,Alligator mississippiensis

Abstract

SUMMARY The effects of treadmill exercise on components of the cardiovascular(heart rate, mean arterial blood pressure, central venous pressure, venous return) and respiratory (minute ventilation, tidal volume, breathing frequency, rate of oxygen consumption, rate of carbon dioxide production)systems and on intra-abdominal pressure were measured in the American alligator, Alligator mississippiensis, at 30°C. Alligators show speed-dependent increases in tidal volume and minute ventilation,demonstrating that the inhibition of ventilation during locomotion that is present in some varanid and iguanid lizards was not present in alligators. Exercise significantly increases intra-abdominal pressure; however,concomitant elevations in central venous pressure acted to increase the transmural pressure of the post caval vein and thus increased venous return. Therefore, despite elevated intra-abdominal pressure, venous return was not limited during exercise in alligators, as was the case in Varanus exanthematicus and Iguana iguana. Respiratory cycle variations in intra-abdominal pressure, central venous pressure and venous return indicate that, at high tidal volumes, inspiration causes a net reduction in venous return during active ventilation and thus may act to limit venous return during exercise. These results suggest that, while tonically elevated intra-abdominal pressure induced by exercise does not inhibit venous return,phasic fluctuations during each breath cycle may contribute to venous flow limitation during exercise.

The accessory role of the diaphragmaticus muscle in lung ventilation in the estuarine crocodile Crocodylus porosus

“…The changes in ventilation and metabolic rates were not as extensive as those previously reported in exercising juvenile alligators (Farmer and Carrier, 2000b;Munns et al, 2005). The discrepancy of our results with those of earlier reports, however, is not surprising given the differences in the species used (Crocodylus versus Alligator), experimental protocol (2min period versus exhaustive exercise) and acclimation to treadmill (none versus extensive).…”

“…Loss of diaphragmatic function disabled the hepatic piston pump, thus aspiration could only be achieved via alterations in intercostal or abdominal muscle activities. The resting breathing patterns of crocodiles in this study at both 20°C and 30°C, and in response to hypercapnia, were similar, both before and after surgery, to those previously measured in juvenile alligators and crocodiles under similar conditions (Farmer and Carrier, 2000c;Hartzler et al, 2006a;Munns et al, 1998;Munns et al, 2005). This suggests that the surgical intervention did not adversely alter the animals' breathing patterns, and the consistency of ventilatory and metabolic data both before and after surgery precluded the need for shamoperated controls.…”

“…While respiratory parameters tend to increase with treadmill speed, cardiovascular responses appear to be 'all or nothing' with maximal increases in heart rate, central venous pressure, arterial blood pressure and venous return reached early in the exercise period, and no further elevations triggered by increasing treadmill speed (Munns et al, 2005). Exercise in crocodilians is also associated with a marked relative hyperventilation (Farmer and Carrier, 2000b;Farmer and Carrier, 2000c;Hartzler et al, 2006b), which was evident in this study by the increased ACR O 2 (Fig. 5) and the decrease in Pa CO2 (Fig. 6).…”

Gestation increases the energetic cost of breathing in the lizard, Tiliqua rugosa

“…Breathing patterns were measured non-invasively using pneumotachography (Glass and Johansen, 1979) using techniques similar to those used in previous studies (Munns and Daniels, 2007;Munns et al, 2004;Munns et al, 2005). A small lightweight mask constructed from the end of a 20ml syringe barrel was fitted over the lizard's nostrils and attached (and the mouth sealed) using dental polyether impression material (Impregum F, Henry Schein Halas, Brisbane, QLD, Australia).…”

Pregnancy limits lung function during exercise and depresses metabolic rate in the skink Tiliqua nigrolutea

“…Breathing patterns were measured non-invasively using pneumotachography (Glass and Johansen, 1979) using techniques similar to those used previously in similar species (Munns, 2013;Munns and Daniels, 2007;Munns et al, 2004Munns et al, , 2005. A small light-weight mask was constructed from the end of a 20 ml syringe barrel.…”