Spirometry is the technique used to measure breathing as part of the diagnosis and monitoring of lung conditions, including asthma and chronic obstructive pulmonary disease (COPD). The tests use a special device and can include the following: Spirometry is the technique used to measure breathing as part of the diagnosis and monitoring of lung conditions, including asthma and chronic obstructive pulmonary disease (COPD). The tests use a special device and can include the following:

• Vital capacity, also known as VC: this refers to the total amount of air that can be exhaled after a full inhalation, which in turn is referred to as the inspiratory capacity.

• Forced expiratory volume (FEV1): This is is the amount of air that can be blown out in one second.

• Forced vital capacity (FVC): also known as peak flow, this is the amount of air that can be blown out after taking a deep breath in until the person feels their lungs are empty.

• Reversibility testing: This involves the patient repeating the one or more of these three tests after using any inhaled medication that they are taking.

In some conditions, the tests will show that air flows more slowly out of the lungs than it should. This is known as an obstructive pattern, and is the case in asthma and COPD when the airways become narrowed. If the amount of air that can be breathed in is decreased but the speed at which it can be exhaled is unchanged because the capacity of the lungs to expand is impaired, it is referred to as a restrictive pattern. This can happen in obesity or pulmonary fibrosis.

In conditions like severe emphysema and cystic fibrosis, both restriction and obstruction are present at the same time. In asthma, FEV1 will be low and reversibility testing may be used to show how well the condition is being managed with the current medication regimen. In COPD, the FEV1/FVC ratio will be below the predicted value for someone’s age, height, gender and ethnicity, and the extent to which this is present dictates how severe the condition is. In mild COPD, FEV1 is 80 per cent or higher than predicted, and will return to normal after reversibility testing. In very severe COPD, FEV1 will be below 30 per cent. In restrictive airways conditions, both FEV1 and FVC will be lower than expected, but the ratio between the two will be unaffected.