Significance of the Crossed Phrenic Phenomenon’ L. JEROME LEWIS AND JOHN M, BROOKHART

T HE THOROUGH and oft-quoted experiments of Porter (I) were designed to determine the presence or absence of crossing connections between the descending inspiratory reticulospinal fibers of one side and the phrenic motor nuclei of the opposite side. In demonstrating the existence of such connections, Porter repeated an observation which had been made previously (z-4) and formulated an hypothesis to account for the facts’ observed. The observation consisted of the following: In an animal with a spinal hemisection above the level of the phrenic nuclei, section of the phrenic nerve on the intact side resulted in the initiation of or increase in activity of the hemidiaphragm on the side of the hemisection. Porter postulated that interruption of the phrenic nerve channeled the descending respiratory impulses away from the phrenic nucleus on the intact side into the phrenic nucleus on the side of the hemisection.