Capsaicin-assessed cough reflex in asthma patients

Abstract

The cough reflex is a primary defensive mechanism for airway protection. Cough disorders are characterized by a change in the threshold for initiating the cough reflex. Various afferent inputs influence the onset and sensitivity of the cough reflex. The study aimed to determine and compare the cough reflex sensitivity between adults with asthma and healthy adults with no history of allergic, respiratory, cardiovascular, gastrointestinal, or endocrine diseases, using European Respiratory Society guidelines on the assessment of cough. We created a group of 52 healthy volunteers (mean age 33.8 years) to serve as a control group for future research into the cough reflex in defined patient groups in upcoming clinical-physiological studies. We found that in the group of healthy volunteers, the threshold concentration of capsaicin required to elicit at least two coughs (C2) was 8.46 micromol/l, while the threshold concentration for inducing at least five coughs (C5) was 26.62 micromol/l. We then compared the reactivity of afferent nerve endings in the airways of healthy adults and adults with asthma by evaluating the differences in the concentrations of capsaicin that elicited C2 and C5 in these two groups. In a group of 19 asthmatic adults (mean age 33 years), the threshold concentration of capsaicin required to induce C2 was 2.03 micromol/l, while the threshold concentration for C5 was 3.02 micromol/l. We demonstrated a significant increase in cough reflex sensitivity in adults with asthma, expressed as the C2 capsaicin concentration (P<0.01) and the C5 concentration (P<0.001). Key words Cough " Cough reflex sensitivity " Capsaicin " Asthma.

Fig. 1

Cough reflex sensitivity evoking two or more coughs in healthy adult subjects (control C2) and asthmatic adult patients (asthma C2) – geometric mean and 95 % CI.

Fig. 2

Cough reflex sensitivity evoking five or more coughs in healthy adult subjects (control C5) and asthmatic adult patients (asthma C5) – geometric mean and 95 % CI.