INTRAPULMONARY CO2-RISE TIME AND VENTILATION IN DUCKS

Many investigators have reported finding intrapulmonary chemoreceptors (IPCs) in several species of birds and reptiles; however, the role of IPCs in ventilatory control in birds has not been identified. This st udy was undertaken to assess the role of intrapulmonary CO2 dynamics o n the control of breathing. Ducks were unidirectionally ventilated, an d their breathing was monitored with a pneumotachograph connected to a personal computer. A gas-mixing system controlled by the computer adj usted the rate of rise of airway CO2 concentration ([CO2]) On inspirat ion, the computer removed CO2 from the ventilating gas for 1.5 s, foll owed by a controlled [CO2] rise. Breathing frequency was directly rela ted to the rate of rise of airway [CO2]. Tidal volume, however, was no t correlated with CO2-rise time but was related to the peak airway [CO 2]. This response is likely mediated by IPCs because preventing airway [CO2] from falling during inspiration immediately altered that breath . An increase in CO2 production (as in exercise) will lead to an incre ase in the rate of CO2 excretion into the lung. The resulting alterati on of breathing frequency would thus maintain acid-base balance. The o bserved response, therefore, may represent a link between ventilation and metabolism.