Gas exchange and ventilation during dormancy in the tegu lizard Tupinambismerianae

The tegu lizard Tupinambis merianae exhibits an episodic ventilatory patter n when dormant at 17 degrees C but a uniform ventilatory pattern when dorma nt at 25 degrees C. At 17 degrees C, ventilatory episodes were composed of 1-22 breaths interspaced by non-ventilatory periods lasting 1.8-26min, Dorm ancy at the higher body temperature was accompanied by higher rates of O-2 consumption and ventilation. The increase in ventilation was due only to in creases in breathing frequency with no change observed in tidal volume. The air convection requirement for O-2 did not differ at the two body temperat ures. The respiratory quotient was 0.8 at 17 degrees C and 1.0 at 25 degree s C. We found no consistent relationship between expired gas composition an d the start/end of the ventilatory period during episodic breathing at 17 d egrees C. However, following non-ventilatory periods of increasing duration , there was an increase in the pulmonary O-2 extraction that was not couple d to an equivalent increase in elimination of CO2 from the lungs. None of t he changes in the variables studied could alone explain the initiation/term ination of episodic ventilation in the tegus, suggesting that breathing epi sodes are shaped by a complex interaction between many variables. The estim ated oxidative cost of breathing in dormant tegus at 17 degrees C was equiv alent to 52.3% of the total metabolic rate, indicating that breathing is th e most costly activity during dormancy.