The effect of antigen-induced bronchoconstriction on phrenic nerve activity

The effects of acute bronchoconstriction, produced by inhalation of Ascaris suum antigen, on both the amplitude and timing of phrenic nerve activity were studied in anesthetized dogs. Blood gas tensions and inspiratory air flow were maintained constant. Bronchoconstriction resulted in a significant increase in the magnitude and rate of rise of the phrenic neurogram during both normal respiratory cycles and cycles when lung inflation was prevented. The increase in the slope of the phrenic neurogram that results from lung inflation was further increased during bronchoconstriction. In addition, in half the animals, there was a significant increase in the tonic phrenic activity measured during expiration. All of these changes were abolished by bilateral cervical vagotomy. Antigen administration did not affect the timing of the different phases of the cycle equally; inspiratory duration was reduced by 51.8% and expiratory duration by 67.6%. Postinspiratory activity of the phrenic (PIIA) was reduced by only 34.7%; thus, during bronchoconstriction PIIA occupied a proportionally greater fraction of the expiratory phase. Vagotomy abolished the changes in respiratory timing and eliminated all PIIA.