The effect of CO2 and temperature on respiratory movements in the chicken

We studied the effect of increasing colonic temperature (Tc) on respiratory amplitude and frequency at different levels of PICO2 in anesthetized, unidirectionally ventilated cockerels. We also evaluated the relationship between PICO2 and PaCO2. Increased PaCO2 augmented respiratory amplitude and decreased frequency at every Tc. Respiratory amplitude increased as Tc rose from 41 to 45 degrees C at each level of PaCO2. During the same rise in Tc, respiratory frequency decreased at the low PaCO2 seen in awake, panting cockerels but increased at eucapnic PaCO2. Tc had no effect on frequency at high PaCO2. Values for respiratory frequency of unidirectionally ventilated cockerels at given Tc and PaCO2 predict those of awake cockerels. We conclude that amplitude of breathing increases in acute hyperthermia unless accompanied by hypocapnia and that without hypocapnia maximal panting frequencies cannot be reached.