Effects of extrapulmonary airway distension on breathing in anesthetized dogs

Anesthetized dogs with open chests were perfused with a pump-oxygenator. We first observed the effects of intermittent periods of sustained inflation of both lungs, of only one lobe, and of an intra-airway balloon on the diaphragm electromyogram (EMG). Lung or lobe inflation with low pressures depressed respiratory frequency (fr) by prolonging expiratory time (TE) in proportion to inflating pressure, but balloon inflation was without effect. We next intermittently inflated one or two lobes after all others were ligated and thereafter inflated all the extrapulmonary airways following total lung excision. Lobe inflation, by varying TE, decreased fr at low pressures and often increased fr at higher pressures. Extrapulmonary airway distension slightly increased fr and the mean rate of rise of the integrated EMG, but decreased inspiratory time and peak EMG amplitude. TE was slightly prolonged by low pressures when using sustained airway pressurization but was shortened by higher pressures when distending cyclically. In comparison to lobe inflation, the effects from isolated airways were small, and the inhibitory effect of lung inflation could not be attributed to them.