Oxidative cost to ventilation in a turtle, Pseudemys floridana.

Estimates of oxidative cost of ventilation for Pseudemys floridana were obtained by comparison of mean resting VO2 with that obtained while artificially ventilating the lungs with a constant air flow in excess of the normal VE, a circumstance during which the animals remained apneic due to reduction in alveolar PCO2. At a body temperature of 22 degrees C, the oxidative cost attributable to ventilation was 0.0047 ml O2/ml gas ventilated, a value about 10 times that of man. This cost of ventilation is then related to values of VO2 and VE at various body temperatures. The oxidative cost of ventilation, expressed as a percentage of resting VO2, is given by the equation: cost = 0.47 VE/VO2. Relative cost declines with body temperature since VE/VO2 (resting) declines according to the equation: VE(BTPS)/VO2 = -0.017 BT -0.025 log Wt + 2.01 where units are in ml, kg and min. At body temperatures of 10 and 37 C relative costs were 30 and 10% VO2, respectively. While the inverse relation between VE/VO2 and body temperature has important implications for regulation of arterial pH through influencing arterial PCO2, it has the additional meaning of reducing the relative oxidative cost of ventilation as VO2 increases.