Subject demographics and baseline characteristics

Healthy volunteersRCCp-value
Age years50.1±14.260.1±13.20.22
Duration of cough years13.0±9.8
BMI kg·m−226.628.10.25
Smoking pack-years0.0 (0.0–0.0)0.0 (0.0–1.8)0.44
FEV1 % pred105.7±13.898.8±16.50.16
FVC % pred107.8±16.0102.7±15.50.31
SNOT score0.08±0.51.3±1.4<0.001
GORD score0.0±3.57.0±15.5<0.001
Capsaicin Emax14.0 (10.5–18.8)27.5 (21.3–37.0)<0.001
Capsaicin ED50 μM·L−115.6 (7.8–31.3)7.8 (3.9–15.6)<0.001
24-h cough frequency coughs·h−10.8 (0.2–1.3)10.9 (8.3–23.7)<0.001
Awake cough frequency coughs·h−11.1 (0.3–1.8)15.4 (12.2–26.7)<0.001
Sleep cough frequency coughs·h−10.1 (0.0–0.6)1.8 (0.5–5.5)<0.001

Data are presented as n, mean±sd or median (interquartile range), unless otherwise stated. RCC: refractory chronic cough; BMI: body mass index; FEV1: forced expiratory volume in 1 s; FVC: forced vital capacity; SNOT: sino-nasal outcome test; GORD: gastro-oesophageal reflux disease; CQLQ: cough quality-of-life questionnaire; Emax: maximum evoked coughs at any dose of capsaicin; ED50: dose evoking at least half the Emax.