Cough receptor sensitivity in children with acute and non-acute asthma

Background - Cough is a major symptom in some children with asthma. The relationship between cough and the severity of asthma is ill defined. A study was undertaken to test the hypotheses that, in children with asthma who cough as a major part of their asthma symptoms, cough receptor sensitivity (CRS) is heightened during an acute severe exacerbation of asthma but not in the non-acute phase and airway calibre or its change correlates with CRS. Methods - Spirometric measurements and the capsaicin CRS test were performed on children admitted to hospital for an acute severe exacerbation of asthma. Nasal secretions were tested for viruses. The children were grouped into those who usually cough with asthma episodes and those who do not. The tests were repeated 7-10 days and 4-6 weeks later. The CRS outcome measure used was the concentration of capsaicin required to stimulate two (Cth) and five coughs (C5). Results - The CRS of the group who coughed (n=15) was significantly higher than those who did not cough (n=16) (mean difference log Cth 0.77 mu mol (95% CI 0.35 to 1.18), C5 0.72 mu mol (95% CI 0.26 to 1.18)) during acute asthma but not after the exacerbation. CRS was not significantly different between groups based on the presence of a viral infection. Neither forced expiratory volume in one second (FEV1) nor its change correlated with CRS nor its change. Conclusions - In children with asthma CRS is heightened in acute severe asthma in the subgroup of children who have cough as a significant symptom with their asthma episodes. In acute and non-acute asthma CRS does not correlate with FEV1.