Exclusion criteria
| Former or current smokers ≥1 pack-yrs |
| Current acute respiratory disease |
| Common cold |
| Acute bronchitis |
| Current respiratory symptoms |
| Cough |
| Wheezing |
| Shortness of breath with rest or exertion |
| Phlegm |
| History of asthma |
| Current treatment with asthma medication |
| History of chronic obstructive pulmonary disease or chronic bronchitis |
| History of other lung diseases |
| Lung operations |
| Pulmonary embolism |