Respiratory inhibition with sympathetic afferent stimulation in the canine and primate.

Inhibition of phrenic efferent nerve activity, diaphragm electromyogram (EMG), and external intercostal EMG was observed in halothane- and pentobarbital-anesthetized mongrel dogs and pentobarbital-anesthetized monkeys with stimulation of sympathetic afferents. The central end of the transected ventral limb of the left ansa subclavia, the sympathetic chain, or individual white rami were stimulated while simultaneously recording phrenic efferent nerve activity, diaphragm EMG, or the external intercostal EMG. Averaged phrenic efferent bursts or MEG were used to trigger an electronic respirator. In all of the dogs and monkeys, electrical stimulation of sympathetic afferent pathways resulted in inhibition of phrenic efferent nerve activity, diaphragm EMG, or external intercostal EMG. Although the exact origin of these fibers was not determined, the conduction velocities of these afferents were 4-7 m/s, which places them in the Adelta fiber-type range. The importance of these afferents in the regulation of respiration in the awake animal remains unknown.