Cough receptor sensitivity and bronchial responsiveness in normal and asthmatic subjects

We examined whether airway cough receptor sensitivity correlates to nonspecific bronchial responsiveness. We measured cough threshold, the lowest concentration of inhaled tartaric acid eliciting five or more coughs, and the provocative concentration of methacholine producing a 20% fall in forced expiratory volume in one second (PC20FEV1) in 38 normal and 11 asthmatic subjects. All subjects were nonsmokers. The geometric mean value of PC20FEV1 was 25.7 mg.ml-1 (GSEM1.29) and 0.63 mg.ml-1 (GSEM1.29) and the geometric mean value of the cough threshold was 115 mg.ml-1 (GSEM1.20) and 95.5 mg.ml-1 (GSEM1.35) in normal and asthmatic subjects, respectively. The PC20FEV1 was significantly (p less than 0.01) lower in asthmatics than in normals but the cough threshold did not differ between them. No significant correlation was observed between the cough threshold and the PC20FEV1 in normal subjects or in asthmatics. These results indicate that cough sensitivity does not directly correlate to bronchial responsiveness in normal and asthmatic subjects.