Phrenic and recurrent laryngeal discharge patterns and the Hering-Breuer reflex

In decerebrate, spontaneously breathing cats, whole-nerve recordings of efferent phrenic (Phr) and recurrent laryngeal (Lar) discharge were analyzed with an average-response computer. The Phr inspiratory (I) burst starts abruptly and has an augmenting discharge pattern which reaches a maximum at the end of the I phase. The Lar I burst starts before onset of the Phr burst (median delay 40ms), reaches an approximately constant level till the end of the I phase. These differences are functionally appropriate for the differing respiratory roles of the innervated muscles (diaphragm and glottis dilators). The Hering-Breuer reflex, produced by occulsion at minimum lung volume (start of the I phase), lengthens the I phase and disinhibits I discarge, but differently for Lar and for Phr activity. Lar activity was increased almost from the start of the I phase. In contrast, occlusion produced no change in the Phr augmenting pattern (slope of activity increase) for most or all of the I phase, indicating that normally vagal inhibitory input shuts off Phr activity in a trigger-like manner.