Meeting Abstract
P2.78 Tuesday, Jan. 5 Cardiac shunting does not constrain aerobic capacity of the American alligator OWERKOWICZ, T.*; EME, J.; GWALTHNEY, J.; BLANK, J.M.; HICKS, J.W.; Uni. California, Irvine; Uni. California, Irvine; Uni. California, Irvine; Uni. California, Irvine; Uni. California, Irvine towerkow@uci.edu
All extant archosaurs possess a four-chambered heart, but differ widely in their aerobic capacity – birds rely more on aerobiosis, whereas crocodilians depend heavily on anaerobic metabolism during activity. We investigated whether this is due to differences in outflow tract design, which allows for cardiac shunting in crocodilians, but not in birds. Cardiac shunting – whereby deoxygenated blood from the right ventricle is sent to the systemic, instead of pulmonary, circulation – may place a constraint on oxygen supply to the tissues at times of increased O2 demand. We hypothesised that removal of cardiac shunt will improve aerobic capacity (VO2max) by forcing the entire right ventricular ejection volume to the lungs. We surgically occluded the left aorta in hatchlings of the American alligator, to render them incapable of shunting. After 17 months of growth and exercise training, we subjected the animals to a graded treadmill exercise test and measured their VO2max. We found no significant difference in VO2max between surgically-altered (7.7 mlO2/kg/min) and sham-operated (8.0 mlO2/kg/min) alligators. To further test whether cardiac shunting occurs during exercise, we measured blood flow in the left and right aortae of juvenile alligators. Shunting (net forward flow in the left aorta) occurred at rest in undisturbed animals, disappeared at the onset of forced exercise, and returned slowly during undisturbed recovery. This suggests cardiac shunting ability does not limit aerobic performance in crocodilians, because the shunt is turned off during exercise. We propose that non-avian theropods may have continued to enjoy benefits of cardiac shunting, even as they evolved a more superior aerobic capacity. Funded by NSF IOB 04445680 to JWH.
