Properties of reversible graded inhibition of phrenic nerve activity by pulmonary afferents.

Reversible graded inhibition of phrenic nerve activity (PNA) was observed during short, low volume lung inflations in chloralose anaesthetized, paralyzed cats. The strength of the inhibitory effect rose with the volume of inflation in a manner suggesting non-linearity. The volume threshold for the first detectable inhibition decreased with increasing delay between onest of inspiration and lung inflation. The differences between the threshold curve for different air flows were not significant. The recovery of PNA from transient inhibition was not immediate and this shows that lung inflations might activate a central inhibitory mechanism, the action of which could outlast the activation period of lung receptors. It is suggested that pulmonary stretch receptors (PSR) are responsible for the observed reactions. The present results indicate that the theory of "all or none" action of PSR on inspiratory activity is not valid for all experimental conditions, and that PSR are capable of continuous control of PNA pattern.