Failure of tracheal distension to inhibit breathing in anesthetized dogs

Using anesthetized spontaneously breathing dogs, we compared the respiratory effects of tracheal distension with the effects of changes in lung volume before and after vagotomy. We used an endotracheal tube with a long cuff to distend the trachea to pressures of 10, 20, and 40 cmH2O. Lung volume increases were imposed by expiratory threshold loading, and volume was decreased by abdominal compression, both of which caused outward rib cage displacement. During expiratory loading, the tidal volume was unchanged but respiratory frequency and minute volume fell and an active expiratory effort appeared; whereas frequency and minute volume rose, but tidal volume fell during abdominal compression. Tracheal distension evoked no discernible change in breathing. Following vagotomy, tidal volume and minute volume fell, and frequency rose slightly, during expiratory loading but abdominal compression was without effect. After vagotomy, 40 cmH2O tracheal distension caused a slight frequency increase. We concluded that the potential role of tracheal deformation in the reflex control of breathing is insignificant in comparison with the other airways.