Intrapulmonary receptor response to changes in airway-gas composition in Gallus domesticus

1. A unidirectional, artificial ventilating system was used to observe respiratory and neural responses to changes in CO(2) concentration in pulmonary airways of the chicken.2. Sectioning any of the three pulmonary branches of the vagus slowed the respiratory response to sudden removal of CO(2) from unidirectional ventilating gas stream.3. The impulse frequency of CO(2)-sensitive units was inversely related to the CO(2) content in the ventilating gas stream.4. Abrupt elimination of CO(2) from the ventilatory gas stream caused a transient burst of activity from CO(2)-sensitive receptors, which quickly adapted to a constant discharge frequency. Fifty percent of the units responded within 0.35 sec after CO(2)-free gas reached the lungs. The neural response to abrupt re-addition of CO(2) to the gas stream was less rapid.5. Acetylcholine or NaCN injected into the pulmonary artery had no apparent effect on the discharge of CO(2)-sensitive receptors. Veratridine temporarily reduced discharge and occasionally produced short, rapid bursts of activity.6. Hypoxia and hyperoxia (5% and 80% O(2)) produced no significant change in the discharge of CO(2)-sensitive receptors.7. Carbon dioxide-sensitive units in spontaneously breathing chickens were silenced by adding 10% CO(2) to the inspired gas; the units responded vigorously to inflation of the respiratory system with a gas containing no CO(2) but remained silent during inflation with gas containing 15% CO(2). Units insensitive to CO(2), which increased their impulse frequency during inflation regardless of the CO(2) content of the inflating gas, also were observed.