Specialist respiratory laboratory tests
The following pulmonary function tests are only performed in specialist respiratory laboratories.
The diffusing capacity of the lung for carbon monoxide (DLCO) is a measure of the capacity of the lungs to transfer gas from alveolar spaces into pulmonary capillary blood (ie the gas exchanging capability of the lung). DLCO can be used to investigate the cause of breathlessness and is useful as a baseline test before starting drugs that can cause pulmonary toxicity (eg amiodarone, leflunomide, methotrexate, some oncology drugs, some biological disease-modifying drugs)1.
Static lung volume measurements are useful in the evaluation of hyperinflation and conditions associated with obstructive and restrictive ventilatory defects. They are also useful for preprocedural evaluation (particularly before lung resection surgery).
Bronchial provocation testing uses spirometry to identify an exaggerated response to a bronchoconstrictor stimulus (airway hyperresponsiveness). It may be used to assist in asthma diagnosis, assess response to asthma therapy, or identify environmental or occupational triggers of asthma. Some occupations may require bronchial provocation testing before employment. Various drugs can interfere with provocation tests (eg beta2 agonists, antimuscarinic and antihistamine drugs)—consult the laboratory about which drugs to avoid before testing.
Exercise testing involves incremental exercise to a symptom-limited maximum on a cycle ergometer or treadmill. It may be used to investigate breathlessness of unknown cause, quantify exercise impairment due to known respiratory disease, assess response to therapy, assess progression of underlying disease, or determine fitness for surgery (especially before lung resection). Exercise-induced bronchoconstriction (exercise-induced asthma) may be investigated using specific treadmill protocols.
The hypoxic challenge test (also known as the high-altitude simulation test) simulates a high-altitude environment and is used to observe hypoxaemia in patients under these conditions. It can be used to assess fitness to fly and risks of travelling to areas of high altitude.