Spinal Intercostal-phrenic Reflexes

Abstract

SOME of the spinal mechanisms involved in the control of the respiratory movements have recently been investigated^1,2. Autogenetic facilitation analogous to the stretch reflex and operating as a “load-compensating reflex” has been demonstrated for the external intercostal muscle^3,4. The other important inspiratory muscle, the diaphragm, seems mainly to be controlled by inhibitory autogenetic effects⁵; so far no facilitation of phrenic α motoneurones has been conclusively demonstrated in response to stretch of the diaphragm or to stimulation of phrenic afferent^4,5. On the other hand, the close functional relation of the intercostal and diaphragm activity as well as the intimate anatomical relation between the diaphragm and the lower part of the rib cage suggest that some kind of close reflex interrelation may exist between these two motor systems. No information about such mechanisms is, however, available. This report presents evidence to support the existence of spinal intercostal-phrenic reflex connexions.