Mechanism of cough and bronchoconstriction induced by distilled water aerosol

We studied the relationship between cough and bronchoconstriction caused by inhaled distilled water aerosol in 8 subjects with asthma by measuring specific airways resistance (SRaw) and recording cough while subjects breathed serially increasing volumes of distilled water or normal saline aerosol produced by an ultrasonic nebulizer. We performed the distilled water dose-response curves after no treatment and after treatment with cromolyn aerosol, lidocaine aerosol, or atropine aerosol in doses of 0.2 mg and 2.0 mg on separate days. Without prior treatment, distilled water aerosol caused cough in 7 of 8 subjects and a marked increase in SRaw in every subject, whereas saline aerosol did not cause cough or a greater than 50% increase in SRaw in any subject. The 2 doses of atropine caused an equivalent reduction in baseline SRaw, but 2.0 mg caused greater inhibition of water-induced bronchoconstriction than did 0.2 mg. Neither dose of atropine inhibited cough. These data suggest that water-induced bronchoconstriction involves cholinergic nerves and that water-induced cough is not dependent on bronchoconstriction. Lidocaine inhibited cough but not bronchoconstriction, whereas cromolyn inhibited bronchoconstriction but not cough, suggesting that cromolyn does not inhibit bronchoconstriction by a generalized inhibition of airway afferent nerves.