HARTZLER, L.K.*; MUNNS, S.L.; HICKS, J.W.; University of California, Irvine; University of California, Irvine; University of California, Irvine: Contribution of Cardiac Shunt to Recovery from an Exhaustive Exercise Bout in the American Alligator, Alligator mississipiensis.

During recovery from an exhaustive exercise bout at 30°C, arterial pH returns to resting levels several hours before the source of the acid-base disturbance (lactate) is cleared. Compensation for this metabolic acidosis is achieved, primarily, by a respiratory alkalosis (significantly depressed P_aCO₂). However, this decrease in P_aCO₂ (34 torr at rest, 25 torr three hours post exercise) is not accompanied by an increase in P_aO₂ suggesting the presence of a right-to-left (R-L) cardiac shunt. This experiment seeks to qualify changes in the shunt patterns from rest and during the recovery period following an exhaustive exercise bout. Preliminary data show extreme variation in shunting patterns in alligators: some alligators show no right-left shunt (left atrial and left aortic arch blood gases are indistinguishable). In contrast, another alligator has matching blood gas values in the right atrium and left aortic arch both at rest and during the recovery period indicating the presence of a persistent R-L shunt. Preliminary data also show an increase in oxygen extraction in those alligators that do not develop a R-L shunt relative to those that do shunt (for example, arterial-venous ΔP_aO₂ of 60 torr vs. 40 torr two hours into recovery). Despite these variations in cardio-respiratory variables, recovery from the acid-base disturbance occurs over a similar time course. These data suggest that alligators may use varying combinations of physiological mechanisms to correct the metabolic acidosis developed during an exhaustive exercise bout and that development of R-L shunt is not required for recovery from acid-base disturbances. Supported by NSF IBN 9982671 to JWH.