| Syndrome | Definition |
| Asthma | Episodic respiratory symptoms |
| Variable airflow obstruction occurring spontaneously, with treatment or after provocation | |
| COPD | Incompletely reversible airflow obstruction |
| Overlap syndrome | Asthma and COPD—that is, symptoms of increased variability of airflow and incompletely reversible airflow obstruction |
| Chronic bronchitis | Symptomatic mucus hypersecretion with cough and sputum daily for at least 3 months over 2 years |
| Emphysema | Abnormal airspace enlargement |
| Variable airflow obstruction | Increased diurnal variability of peak flow: maximum–minimum/average >10% |
| Increased response to bronchodilator: >200 ml FEV1 and >12% baseline | |
| Increased airway responsiveness: provocation dose or concentration <normal | |
| Incompletely reversible airflow obstruction | Postbronchodilator FEV1 <80% predicted and FEV1/FVC <70% |
| Bronchodilator responsiveness | Improvement in FEV1 >15% and 400 ml after a therapeutic dose of inhaled rapid acting β2-agonist |
| Airway hyper-responsiveness | Significant fall in FEV1 from a stable baseline after inhalation of bronchial provocation stimulus occurring at a stimulus dose less than required to induce a significant change in FEV1 in healthy controls. |
COPD, chronic obstructive pulmonary disease; FEV1, forced expiratory volume in 1 s; FVC, forced vital capacity.