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Surgical Removal of Right-to-Left Cardiac Shunt in the American Alligator (Alligator Mississippiensis) Causes Ventricular Enlargement But Does Not Alter Apnoea or Metabolism During Diving
Journal of Experimental Biology
  • John Eme, University of California - Irvine
  • June Gwalthney, University of California - Irvine
  • Jason M. Blank, California Polytechnic State University - San Luis Obispo
  • Tomasz Owerkowicz, University of California - Irvine
  • Gildardo Barron, University of California - Irvine
  • James W. Hicks, University of California - Irvine
Publication Date
11-1-2009
Abstract
Crocodilians have complete anatomical separation between the ventricles, similar to birds and mammals, but retain the dual aortic arch system found in all non-avian reptiles. This cardiac anatomy allows surgical modification that prevents right-to-left (R–L) cardiac shunt. A R–L shunt is a bypass of the pulmonary circulation and recirculation of oxygen-poor blood back to the systemic circulation and has often been observed during the frequent apnoeic periods of non-avian reptiles, particularly during diving in aquatic species. We eliminated R–L shunt in American alligators (Alligator mississippiensis) by surgically occluding the left aorta (LAo; arising from right ventricle) upstream and downstream of the foramen of Panizza (FoP), and we tested the hypotheses that this removal of R–L shunt would cause afterload-induced cardiac remodelling and adversely affect diving performance. Occlusion of the LAo both upstream and downstream of the FoP for ~21 months caused a doubling of RV pressure and significant ventricular enlargement (average ~65%) compared with age-matched, sham-operated animals. In a separate group of recovered, surgically altered alligators allowed to dive freely in a dive chamber at 23°C, occlusion of the LAo did not alter oxygen consumption or voluntary apnoeic periods relative to sham animals. While surgical removal of R–L shunt causes considerable changes in cardiac morphology similar to aortic banding in mammals, its removal does not affect the respiratory pattern or metabolism of alligators. It appears probable that the low metabolic rate of reptiles, rather than pulmonary circulatory bypass, allows for normal aerobic dives.
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Publisher statement
Published by Company of Biologists.
Citation Information
John Eme, June Gwalthney, Jason M. Blank, Tomasz Owerkowicz, et al.. "Surgical Removal of Right-to-Left Cardiac Shunt in the American Alligator (Alligator Mississippiensis) Causes Ventricular Enlargement But Does Not Alter Apnoea or Metabolism During Diving" Journal of Experimental Biology Vol. 212 Iss. 21 (2009) p. 3553 - 3563
Available at: http://works.bepress.com/jmblank/3/