Somatic afferent activity in reflex regulation of diaphragmatic function in the cat

¹ Department of Physiology, University of Kentucky, Lexington, Kentucky

Experiments were performed to disclose the functional role of afferent activity from the diaphragm, previously described as proprioceptive. Electromyographs were recorded by leads placed in the diaphragm of anesthetized and decerebrate cats. The experiments indicate that in basal conditions interruption of the afferent connections from the diaphragm (i.e., section of the appropriate dorsal roots) did not change the electromyographic activity of the diaphragm. Even during maneuvers known to increase the afferent discharges from the diaphragm, such as negative pressure breathing and abdominal compression, division of the afferent inflow failed to cause a consistent change in the electromyographic patterns of the diaphragm activity. The vagal reflexes from the lungs (Hering-Breuer) remained the same with and without somatic deafferentation. Electrical stimulation of the cervical roots constantly evoked a polysynaptic response recorded either from the diaphragm or the phrenic nerves. This reflex response, without a monosynaptic component, cannot represent a potential myotatic reflex mechanism. The results of these experiments indicate an absence of proprioceptive drive in the reflex regulation of diaphragmatic function.