Activities of pulmonary stretch receptors during ventilatory cycles without lung inflation

When lung inflation is temporarily withheld in paralyzed, ventilated cats with intact vagi, the activities of inspiratory motor nerves are greater during the second cycle without inflation than during the first. This response is not easily attributable to increasing drive from chemoreceptors as it is abolished by vagotomy. We examined the hypothesis that the increasing inspiratory activity is the result of decreasing inhibitory feedback from pulmonary stretch receptors (PSRs). Decerebrate, paralyzed cats were ventilated by a servo-respirator in accordance with their own phrenic nerve activity. Afferent activities from individual PSRs were recorded from a few cut fibers of one vagus nerve; the vagi were otherwise intact. When lung inflation was withheld, phrenic and hypoglossal nerve activities and the durations of inspiration and expiration all increased and were significantly greater during the second cycle without inflation than during the first. The frequency of PSR discharge was also greater during the second cycle and thus did not account for the responses recorded from the motor nerves. We conclude that the latter responses probably reflect neural processes within the brain stem, involving a persistent inhibitory influence from lung inflation, which outlasts the inflation itself.