| Abstract: | We have investigated the possibility that afferent vagal stimuli may be responsible for the excessive ventilatory drive during exercise characteristic of many diffuse pulmonary parenchymal diseases. Studies were performed on four conscious dogs with cervical vagal loops, in whom experimental pneumonitis was induced by the intravenous administration of complete Freund's adjuvant. Control measurements were made over a 3-mo interval prior to induction of disease which then ran a course of 6 wk. The disease was characterized histologically by a diffuse interstitial pneumonitis during the first week, and by a proliferative granulomatosis during the subsequent 4-5 wk. Physiologic disturbances at rest included decreased total lung and functional residual capacities; increased lung elastic recoil; and decreased carbon monoxide diffusing capacity. During mild-to-moderate steady-state exercise, the minute volume of ventilation (VE) and respiratory frequency (f) were increased significantly compared to control values; tidal volume (VT) was decreased significantly; and exercise tolerance (ET) was impaired. Complete cervical vagal blockade abolished the abnormally high VE, decreased f, and increased VT in all dogs, and improved ET in at least two dogs. The results indicate that afferent vagal stimuli were responsible for the excessive ventilation during exercise and contributed to the abnormal pattern of breathing. |
