Hypertonic saline cough provocation test with salbutamol pre-treatment: evidence for sensorineural dysfunction in asthma.

BACKGROUND: Cough is one of the most common symptoms of asthma. However, studies using capsaicin, citric acid, or tartaric acid to document cough threshold have repeatedly failed to show statistically significant differences between asthmatic and healthy subjects. The studies using hypertonic aerosols as the cough stimulant have suggested an enhanced sensitivity in asthmatic subjects but the induced bronchoconstriction has made the interpretation of the results difficult.
OBJECTIVE: To determine the cough sensitivity to hypertonicity in healthy subjects, patients with chronic cough, and patients with asthma in a setting where the induction of bronchoconstriction is prevented.
METHODS: Nineteen healthy subjects, 21 non-asthmatic patients with chronic cough, and 26 asthmatic patients with chronic cough underwent an incremental hypertonic saline challenge including a pre-treatment with 0.4 mg of salbutamol. Spirometry was performed before the challenge, after salbutamol, and after the challenge. The patients with cough also underwent skin testing, histamine challenge, exhaled nitric oxide measurement, ambulatory peak flow monitoring, kept cough diary, and filled in the Leicester Cough Questionnaire. Eighteen patients repeated the saline challenge.
RESULTS: The challenge did not induce bronchoconstriction in any group. The osmolality to provoke 15 cumulative coughs was significantly smaller in the asthmatic patients than in the healthy subjects (P<0.001) and in the cough patients without asthma (P=0.04). According to multivariate analysis among all the 47 patients with cough, female sex (P<0.001) and large spontaneous peak flow variation in the ambulatory recording (P=0.001) were associated with high sensitivity to saline. The saline challenge response was well repeatable (intraclass correlation coefficient 0.90).
CONCLUSION: The findings of the present study are not affected by induced bronchoconstriction. Asthma or, more specifically, spontaneous, reversible airway obstruction is associated with an enhanced sensitivity to the cough-provoking effect of hypertonic saline. This suggests a pathological function of the sensorineural apparatus in this disorder.