Rapid, shallow breathing after Ascaris suum antigen inhalation: role of vagus nerves

In 5 treadmill-exercising, unsedated dogs, we studied the effect of inhaled Ascaris suum antigen aerosols on minute volume of ventilation (VE), respiratory frequency (f), tidal volume (VT), total pulmonary resistance (RL), and dynamic pulmonary compliance (CL(dyn)), before and during cooling of the vagus nerves. With the vagi warm, inhaled antigen increased VE (mean + 62%; P < 0.01) by increasing f (mean + 180%; P<0.01), despite a decrease in VT (mean - 42%; P<0.01). RL increased (mean + 170%; P < 0.001) and CL(dyn) decreased (mean - 43%; P< 0.005). With the vagi cool, inhaled antigen no longer affected VE, f, or VT (P > 0.5), although RL still increased and CL(dyn) still decreased. Inhalation of a bronchodilator, terbutaline, prevented the broncho-constriction induced by antigen but did not prevent the ventilatory response. We conclude that vagal afferent pathways mediate the ventilatory response to inhaled antigen and suggest that the primary stimulus for this response is not airway narrowing.