Interaction of temperature with extra- and intrapulmonary chemoreceptor control of ventilatory movements in the awake...

Several studies in artificially ventilated, anesthetized birds with opened thoracoabdominal cavities have shown that intrapulmonary chemoreceptors (IPC) sensitive to CO2 contribute to the control of ventilatory movements. Increasing colonic temperature (Tc) has been shown to increase depth and decrease frequency of ventilatory movements if PaCO2 is held constant at less than 35 torr in awake and anesthetized, artificially ventilated cockerels. The relative importances, though, of IPC and of extrapulmonary CO2-sensitive chemoreceptors (EPC) in controlling ventilation in the awake or hyperthermic bird is unknown. We dissociated the PCO2 affecting IPC and EPC in awake cockerels by ligating the left pulmonary artery, denervating the IPC in the right lung and artificially ventilating each lung separately. We found, that at constant PaCO2, ventilatory movements increased in depth and decreased in frequency with: (1) increasing PICO2 to the innervated, non-perfused lung (PipcCO2); and (2) increasing Tc. Similar responses were observed with increasing PaCO2 or Tc during constant PipcCO2. Multiple regression analyses show that IPC and EPC have about equal controlling influences on ventilatory movements in the awake and hyperthermic cockerel.