Temperature effects on ventilation and metabolism in the lizard, Ctenophorus nuchalis

The effect of temperature upon ventilation and metabolism was measured on a breath by breath basis in the lizard Ctenophorus nuchalis. This species displayed a typical reptilian breathing pattern; groups of breaths separated by periods of breath holding. The lengths of the non-ventilatory periods (NVP) decreased as temperature increased. As a result, overall breathing frequency (f) displayed a thermal dependence. Outside the preferred temperature range (27-37 degrees C) f was also affected by changes in the frequency of breathing that occurred during periods of ventilation (f'). On the other hand, tidal volume (VT) was maintained constant at all temperatures except 42 degrees C ('panting' threshold). Thus, due to the thermal dependency of f, ventilation (VE) displayed a significant increase between 18 and 37 degrees C. Metabolism (VO2 and VCO2) also increased within this temperature range. However, as a result of a lower Q10 for ventilation, ventilatory requirement (VE/VO2 and VE/VCO2) decreased. In addition, lung volume (LV) increased with temperature. Examination of the alveolar ventilation-PCO2 relationship revealed that as a result of the increase in LV the level of intrapulmonary CO2 at the end of an NVP was maintained irrespective of temperature. This implies a temperature-independent chemical threshold for the onset of breathing. It is postulated that with temperature the observed increase in LV could offset the increase in metabolism by slowing the rise of intrapulmonary CO2 levels. This would delay the onset of breathing which in turn would lower VE/VCO2 (and VE/VO2) by preventing an effectual hyperventilation. This supports the notion, at least in C. nuchalis, that relative alkalinity is maintained.