A FURTHER STUDY OF THE CROSSED PHRENIC PHENOMENON

Abstract

The appearance of crossed diaphragmatic contractions[long dash]i.e., ipsilateral to a spinal semisection at C2 or C3[long dash]was studied in rabbits and cats in the following conditions animals in which the phrenic nerve contralateral to the spinal semi-section had been cut and anastomosed either to the cervical sympathetic or the denervated sternomastoid muscle 1 to 25 wks. previously; animals in which the respiratory center or the respiratory tract above C3 was stimulated electrically ; animals in which the active phrenic on the side contralateral to the spinal semisection was blocked reversibly by alternating or direct currents of varying intensities and durations; during activation of the respiratory center either reflexly or by asphyxia, before and after application of reversible blocks to the active phrenic. The effects of cutting the vagi before or after reversible diaphragmatic crossings are described. The changes of respiratory rate during crossings are reported. Results indicate that: crossed contractions occur directly as a result of cutting or blocking the motor fibers, not as an indirect effect from relative asphyxia or from changes in the afferent impulses set up by respiratory movements; the central changes are mediated by some process which does not require the conduction of nerve impulses; once the crossed path has been opened[long dash]i.e., after a reversible block[long dash]subsequent crossings are more readily obtained.