title: Terrestrial locomotion does not constrain venous return in the American alligator, Alligator mississippiensis.
abstract: 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 degrees 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.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, 321 Steinhaus Hall, Irvine, CA 92697, USA. suzy.munns@jcu.edu.au
authors.forename: Suzanne L
authors.initials: SL
authors.lastname: Munns
authors.forename: Lynn K
authors.initials: LK
authors.lastname: Hartzler
authors.forename: Albert F
authors.initials: AF
authors.lastname: Bennett
authors.forename: James W
authors.initials: JW
authors.lastname: Hicks
mesh_terms: D000489:Alligators and Crocodiles / Q000502:physiology*; D000818:Animals; D001775:Blood Circulation / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D002245:Carbon Dioxide / Q000378:metabolism; D006339:Heart Rate / Q000502:physiology; D008124:Locomotion / Q000502:physiology*; D008145:Louisiana; D010101:Oxygen Consumption / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D015656:Respiratory Mechanics / Q000502:physiology*; D013990:Tidal Volume / Q000502:physiology; D014680:Veins / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide