Augmented breath provoked by lung inflation in cat.

The rate of occurrence and magnitude of provoked augmented breath (PAB) were studied as the function of lung expansion applied at different intervals (15-180 s). Together with phrenic nerve activity (Phr.) the activities of recurrent laryngeal (RL) and hypoglossal (Hyp) nerves were investigated during PAB. The experiments were carried out in 10 cats anesthetised, paralysed and artificially ventilated by means of a phrenic nerve-driven respiratory. Lung expansion was performed by increasing the gain of the servorespirator for one breath. PAB could be elicited when the interval between subsequent inflations was longer than 30 s ("refractory time"). We did not find out any consistent relationship, common for all experiments, between the value of the interval (greater than 30 s) and the rate of occurrence of PAB as well as between the volume of lung inflation and the magnitude of PAB. During PAB registered on Phr., activities of RL and Hyp were usually inhibited. It is concluded that PAB depends upon the instantaneous balance of excitatory and inhibitory vagal influences centrally differentiated at various respiratory outputs. Its amplitude and occurrences are therefore difficult to predict. Thus, PAB can be hardly compared with spontaneous deep breath.