Respiratory reflexes evoked by tracheal distension.

In 13 dogs that were anesthetized and ventilated through an endotracheal tube, segments of either the intrathoracic (ITT) or extrathoracic trachea (ETT) were distended by over-inflating the sealing cuff within the first half of an inspiration and maintaining this overinflation for two breathing cycles. ITT distension caused a significant prolongation of the expiratory duration (TE) of the first challenged breath in 12 of the 13 dogs. ETT distension prolonged the TE in only 5 of the 13 dogs. An inhibition of inspiration resulting in shortened inspiratory time and reduced peak phrenic amplitude (PPA) was measured in three experiments. In six other experiments, there was only a transient decrease in phrenic discharge, which immediately resumed. In the remaining four experiments, the inspiratory burst was unaffected. After vagotomy, ITT distension shortened TE in 8 of the 13 dogs. ETT distension was ineffective in 10 out of 11 experiments; in the remaining experiment TE was significantly lengthened. No significant effects were elicited on TI and PPA by either ITT or ETT distension. These results could be explained by the known behavior of tracheal receptors and could indicate the presence of extravagal influences.