Cyclic Carbon Dioxide Exchange in the Turtle Pseudemys scripta

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Abstract
Pseudemys scripta lung volume decreases with increasing apneic time to an extent greater than predicted by the organismic respiratory quotients (RQ). Lung volume change is due primarily to sequestration of CO₂ in body fluids and minimally to nonpulmonary CO₂ loss. The stored CO₂ is pulsed into the lung during the brief ventilatory phase of the respiratory cycle and is recoverable in expired gas at an appropriate RQ. The observed pattern of cyclic CO₂ exchange is related to the decline in blood capacitance for CO₂ and to right-to-left intracardiac shunting during apnea. Maximum voluntary diving time in the laboratory appears to be terminated at a critical (lung gas) of about 22 torr. Such dives appear to be aerobic.

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