The measurement of exhalation strength is important to detect and treat obstructive (constricted) respiratory diseases. The narrowing of the airway makes breathing difficult, even causing respiratory distress. Examples of obstructive respiratory diseases are COPD (Chronic Obstructive Pulmonary Disease), emphysema, chronic bronchitis, bronchiectasis (bulging of the bronchi) and asthma.
One measure of airway distance is the maximum speed (peak flow) at which a person can exhale air. The result of a peak flow measurement is given in litres per minute.
Regular peak flow measurements can detect even small changes in lung condition. This makes it easier to assess the effect of the medication.