Patient’s characteristics at enrolment (n = 68)
| Age | 74 (7.3) | mMRC scale, grade | 1.6 (1.2) |
| Body mass index, kg/m2 | 21.6 (3.3) | CAT, point | 13 (8) |
| Sex, male | 58 (85.3) | LCQ, point | 18.4 (2.6) |
| Smoking, ex/current | 54 (79.4)/14 (20.6) | Neutrophils, /µL | 3978 (1557) |
| Pack-years | 56.5 (31.1) | Eosinophils, /µL | 249 (207) |
| GOLD classification, A/B/C/D | 19 (27.9)/ 23 (33.8)/ 6 (8.8)/ 20 (29.4) | Eosinophils ≥300/ µL† | 12 (17.6) |
| COPD stage 1/2/3/4 | 14 (20.6)/38 (55.9)/ 12 (17.6)/4 (5.9) | Albumin, g/dL | 4.0 (0.3) |
| Long acting muscarinic antagonists use, + | 48 (70.6) | Lactate dehydrogenase, IU/L | 195 (35) |
| Long acting β2 agonists use, + | 57 (83.8) | Haemoglobin A1c, % | 6.0 (0.8) |
| Inhaled corticosteroids use, + | 21 (30.9) | Brain natriuretic peptide, pg/mL | 64.5 (95.2) |
| Home oxygen use, + | 9 (13.2) | C reactive protein, mg/L* | 0.31 (0.50) |
| Pneumococcal vaccination, + | 34 (50) | IgE, IU/L† | 361 (610) |
| Asthma, + | 10 (14.7) | FeNO, ppb | 25.9 (16.4) |
| Cerebrovascular disease, + | 7 (10.3) | C2, the number of doubling concentration | 4.7 (2.6) |
| Pneumonia <2 year, + | 20 (29.4) | C5, the number of doubling concentration | 5.8 (2.5) |
| Frequent pneumonia (≥2), + | 5 (7.4) | C5≤2.44 µM | 5 (7.4) |
| Acute exacerbation <2 year, + | 19 (27.9) | Ejection fraction, %* | 64.2 (22.3) |
| Frequent acute exacerbation (≥2), + | 8 (11.8) | Postbronchodilator FEV1, mL | 1618 (668) |
| Hospitalisation, + | 34 (50) | Postbronchodilator FEV1 predicted, % | 64.2 (22.4) |
| Hospitalisation<2 year, + | 27 (39.7) | Postbronchodilator FEV1/FVC, % | 50.0 (12.6) |
| Frequent hospitalisation (≥2), + | 10 (14.7) | Reversibility, % | 4.6 (8.1) |
Global initiative for chronic obstructive lung disease.
The number of doubling concentration was shown as follows; eg, 0.61 µM, 1.22 µM, 2.44 µM, 4.88 µM, 9.76 µM, 19.52 µM, 39.04 µM, 78.1 µM, 156.2 µM and 312.5 µM correspond to 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 doubling concentrations, respectively. *n =66, †n = 64.
C2 and C5, concentrations of inhaled capsaicin required to induce at least two (C2) and five coughs (C5); CAT, COPD assessment test; FeNO, fractional nitric oxide; FEV1, forced expiratory volume in 1s; FVC, forced vital capacity; Ig, immunoglobulin; LCQ, Leicester Cough Questionnaire; mMRC, modified Medical Research Council.