MECHANISM OF COUGH AND BRONCHOCONSTRICTION INDUCED BY DISTILLED WATER AEROSOL

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Abstract
Relationship between cough and bronchoconstriction caused by inhaled distilled water aerosol was studied in 8 [human] 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. The distilled water dose-response curve was performed 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; saline aerosol did not cause cough or a > 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. Water-induced bronchoconstriction involves cholinergic nerves. Water-induced cough is not dependent on bronchoconstriction. Lidocaine inhibited cough but not bronchoconstriction; cromolyn inhibited bronchoconstriction but not cough, suggesting that cromolyn does not inhibit bronchoconstriction by a generalized inhibition of airway afferent nerves.