An increase in the threshold of citric acid-induced cough during chest wall vibration in healthy humans

This study tested the hypothesis that the afferent input from the respirato ry muscles may be involved in the neural mechanisms inducing cough response s. Coughing was evoked in conscious healthy humans by the inhalation of cit ric acid aerosol of several concentrations either during or not during ches t wall vibration (100 Hz) at the right second intercostal space or during v ibration of the right thigh. The mean threshold citric acid concentration t o induce coughing was significantly higher during chest wall vibration (geo metric mean, 131.8 mg/ml) than without vibration (75.9 mg/ml). Vibration af ter topical anesthesia of the chest wall skin did not significantly change the threshold concentration of citric acid. The threshold citric acid conce ntration during vibration of the right thigh did not significantly differ f rom that without vibration. We concluded that inputs from the chest wall af ferent, presumably from the intercostal muscle or costovertebral joint, may have an inhibitory effect on the initiation of coughing at the higher neur al structure in conscious humans.