Incident respiratory symptoms during follow up according to the level of airway responsiveness in subjects asymptomatic at baseline
| Level of airway responsiveness (PC20)(mg/ml) | No of subjects | No of incident respiratory symptoms* | ||
|---|---|---|---|---|
| 2 | ⩾3 | ⩾2† | ||
| PC20, concentration of methacholine provoking a 20% fall in FEV1; AHR, airway hyperresponsiveness. | ||||
| *Wheezing, shortness of breath, chest tightness, cough, respiratory complaints upon exertion. | ||||
| †Percentage of subjects complaining of two or more new respiratory symptoms among those with a given PC20 level who developed new respiratory symptoms. | ||||
| ⩽4 | 19 | 5 | 4 | 9/19 (47.4%) |
| 4–8 | 19 | 4 | 0 | 4/19 (21.1%) |
| With AHR | 38 | 13 (34.2%) | ||
| 8–16 | 36 | 8 | 6 | 14/36 (38.9%) |
| 16–32 | 41 | 5 | 3 | 8/41 (19.5%) |
| 32 | 313 | 8 | 1 | 9/313 (2.9%) |
| Without AHR | 390 | 31/390 (7.9%) | ||
| Overall | 428 | 30 | 14 | 44/428 (10.3%) |