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First published online November 14, 2008
Journal of Experimental Biology 211, 3759-3763 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.021089

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Changes in pulmonary blood flow do not affect gas exchange during intermittent ventilation in resting turtles

Tobias Wang^1,2,* and James W. Hicks²

¹ Zoophysiology, Department of Biological Sciences, University of Aarhus, 8000 Aarhus C, Denmark
² Department of Ecology and Evolutionary Biology, University of California at Irvine, Irvine, CA 92697, USA

^* Author for correspondence (e-mail: tobias.wang{at}biology.au.dk)

Accepted 11 September 2008

The breathing pattern of many different air-breathing vertebrates, including lungfish, anuran amphibians, turtles, crocodiles and snakes, is characterized by brief periods of lung ventilation interspersed among apnoeas of variable duration. These intermittent ventilatory cycles are associated with characteristic increases in pulmonary blood flow and tachycardia. In animals with central vascular shunts, the rise in pulmonary blood flow during ventilation is associated with the development of left-to-right (L–R) cardiac shunt (pulmonary recirculation of oxygenated blood returning from the lungs). By contrast, a large net right-to-left (R–L) shunt (pulmonary bypass) normally prevails during apnoea. The cardio–respiratory interaction and the changes in cardiac shunting have been suggested to improve pulmonary gas exchange but the benefits of L–R shunting on pulmonary gas transport have not been studied experimentally. The present study measured pulmonary gas exchange in fully recovered, freely diving turtles, where changes in pulmonary blood flow were prevented by partial occlusion of the pulmonary artery. Prevention of L–R shunt during ventilation did not impair CO₂ excretion and overall, oxygen uptake and CO₂ excretion did not correlate with changes in pulmonary blood flow. We conclude that increases in pulmonary blood flow associated with ventilation are not required to maintain resting rates of oxygen uptake and CO₂ excretion in resting animals.

Key words: reptile, turtle, periodic ventilation, pulmonary blood flow, cardiac shunt, left-to-right shunt, gas exchange, CO₂ excretion, respiratory gas exchange ratio

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