Changes in breathing pattern mediated by intrapulmonary CO2 receptors in chickens.

The ventilation of unanesthetized tracheostomized chickens was measured using a whole-body plethysmograph. The inspired CO2 fraction was quickly manipulated between 0.05 and 0.0 in such a way as to limit the fresh air inspired to a fixed duration pulse preceded and followed by 5% CO2. As was previously shown with this experimental protocol [Tallman et al., Am. J. Physiol. 237 (Regulatory Integrative Comp. Physiol. 6): R260-R265, 1979], the duration of inspiration and expiration (TI and TE, respectively) was dependent on the timing, relative to inspiration, that the pulse of air arrived at the lung. To study the possible involvement of arterial chemoreceptors in this reflex, a method of denervating the carotid chemoreceptors in this reflex, a method of denervating the carotid bodies was developed. After denervation, the hyperpneic response to intravenous NaCN and 2-3 breaths of N2 was eliminated, indicating the complete removal of arterial chemoreflexes. When tested with the same protocol of CO2 inhalation following carotid body denervation, TI and TE were still dependent on the delay of the fresh air pulse. These experiments support the conclusion that intrapulmonary CO2 receptors (IPC) mediate the reflexes studied and provide evidence that IPC affect the phase-switching mechanisms on a breath-to-breath basis.