Inhibition of breathing associated with gallbladder stimulation in dogs

The effect of mechanical stimulation of the gallbladder on breathing was studied in anesthetized spontaneously breathing dogs. Measurements of tidal volume, breathing frequency, rib cage and abdominal diameter, transdiaphragmatic pressure, and electrical activity of the diaphragm were made while traction or compression was applied to the gallbladder for periods of 30 s. Both forms of mechanical stimulation produced similar changes, including large decreases in tidal volume, respiratory rate, electrical activity of the diaphragm, and transdiaphragmatic pressure swings. Inspiratory rib cage expansion was little affected, but abdominal expansion was greatly reduced, and swings in gastric pressure were reduced more than swings in pleural pressure, indicating a selective decrease in diaphragmatic activity. Recovery of all measured parameters returned toward control values, despite continued traction or compression. Some inhibition persisted after the stimulus was withdrawn. The very brief interval between stimulus and response suggested that the mechanism was a neural reflex. The afferents involved are unknown but are not purely vagal in nature, since qualitatively similar results were seen in animals after vagotomy. The alteration in breathing frequency indicates that at least part of the reflex is supraspinally mediated. The change in pattern of breathing closely resembles that seen in subjects after abdominal surgery and supports the theory that reflex inhibition of breathing contributes to postoperative pulmonary complications seen in those subjects.