Analysis of efferent discharges of the phrenic nerve during the cough reflex.

The response of the phrenic nerve activities during the cough reflex was investigated in anesthetized dogs. The phrenic nerve activities were recorded from the central cut end of the nerve. Changes in phrenic nerve activities were evaluated by means of computer analysis using the programs for power spectrum, amplitude histogram, pulse density variation, and autocorrelation. The cough reflex was induced by mechanical stimulation of the tracheal mucosa. The cough reflex evoked was accompanied by an increase in the number of spike potentials and shortening of the respiratory burst period of the phrenic nerve activities. There was a significant correlation between the intensity of expiration and the multiplication product of the mean amplitude of spike potentials and spike numbers of the phrenic nerve activities during the cough reflex. Total activity of the discharge, amplitude of spike potentials, and pulse density of the phrenic nerve activities also increased during the cough reflex, while the autocorrelation coefficient decreased. These changes were inhibited by codeine. The responses of the phrenic nerve activity during the cough reflex were also observed under artificial respiration as well as under spontaneous respiration. These findings indicate that the phrenic nerve activity can be an indicator of the cough reflex, and it is useful for the indicator to investigate the central mechanisms of the cough reflex.