The activity of lung afferent nerves during tracheal occlusion

Abstract

We have recorded the activity of 72 pulmonary stretch receptors isolated from 34 rabbits and 19 receptors isolated from 3 cats both with the animal breathing through an open tracheal tube and against a closed airway. In the first breath during airway occlusion done at FRC 36.1% of the receptors showed an increase of firing during the inspiratory effort compared with the expiratory pause (inspiratory modulation). 47.2% of the receptors showed no change in firing frequency between the two phases of the respiratory effort and 16.7% increased their firing during the expiratory phase (expiratory modulation). However, the average modulation during the first occluded breath was only 7% of that observed in control breathing in rabbits and 2% in cats so the overall frequency of stretch receptors discharge ascending the vagus nerves hardly varied from inspiration to expiration. During the first occluded breath some of the stretch receptors normally silent at FRC became active while others increased their activity. This departure from FRC activity amounts to 6% of the increase in frequency of discharge observed in control breathing. We interpret the behaviour of pulmonary stretch receptors during occluded breathing as due to some re-distribution of air within the lung or some deformation of the airway. We have also studied 8 irritant receptors: 6 in rabbits and 2 in cats. All were active during the control breathing and their activity diminished when the airway was occluded. When the airway was re-opened these receptors showed a greatly augmented activity. This last observation could explain the augmented breath observed after a period of airway occlusion.