Effects of temperature transients on gas exchange and acid-base status of turtles

Pulmonary ventilation (VE), O2 consumption (VO2), and CO2 production (VCO2) were measured continuously on each of 10 turtles, Pseudemys scripta elegans, at 20 degrees C, during and for 1 h after heating to 30 degrees C and during and for 1 h after cooling to 20 degrees C. In seven of the animals, arterial blood was sampled at the three temperature plateaus. Ventilatory ratios (VE/VO2 and VE/VCO2) and metabolic rate adjusted promptly to temperature change, stabilizing at values similar to those observed previously in turtles following 1 day or more at each temperature. Likewise, mean blood pH and PCO2 values conformed both in absolute values and in temperature-dependence to data previously obtained from animals exposed to the various temperatures for longer time periods or from turtle blood thermally equilibrated in vitro. Total plasma [CO2] did not change significantly, suggesting that steady-state CO2 exchange prevailed throughout the experiment. In accordance with this, R(VCO2/VO2) did not change significantly during the 20-30 degrees C transition; however, R rose during the 30-20 degrees C transition, suggesting possible hyperventilation at this stage. We conclude that the respiratory control of blood acid-base status adjusts rapidly to temperature change in the turtle and its adjustment minimizes disturbance to CO2 balance.