Abstract
1. A unidirectional, artificial ventilating system was used to observe respiratory and neural responses to changes in CO2 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 CO2 from unidirectional ventilating gas stream.
3. The impulse frequency of CO2-sensitive units was inversely related to the CO2 content in the ventilating gas stream.
4. Abrupt elimination of CO2 from the ventilatory gas stream caused a transient burst of activity from CO2-sensitive receptors, which quickly adapted to a constant discharge frequency. Fifty percent of the units responded within 0·35 sec after CO2-free gas reached the lungs. The neural response to abrupt re-addition of CO2 to the gas stream was less rapid.
5. Acetylcholine or NaCN injected into the pulmonary artery had no apparent effect on the discharge of CO2-sensitive receptors. Veratridine temporarily reduced discharge and occasionally produced short, rapid bursts of activity.
6. Hypoxia and hyperoxia (5% and 80% O2) produced no significant change in the discharge of CO2-sensitive receptors.
7. Carbon dioxide-sensitive units in spontaneously breathing chickens were silenced by adding 10% CO2 to the inspired gas; the units responded vigorously to inflation of the respiratory system with a gas containing no CO2 but remained silent during inflation with gas containing 15% CO2. Units insensitive to CO2, which increased their impulse frequency during inflation regardless of the CO2 content of the inflating gas, also were observed.
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Selected References
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