Clinical application of respiratory function tests

Abstract

Before requesting or performing tests of respiratory function it is worth while to pause and consider the question ‘What information is required?’, since the answer will determine which tests are appropriate. Clearly this will depend on the clinical context: possible answers would include assessment of the severity of airflow obstruction, screening for abnormality in a patient with breathlessness of uncertain cause, identification of a response to steroids in a patient with fibrosing alveolitis, etc. Tests of respiratory function have obvious limitations as specific diagnostic tools. What they can do is (1) identify an abnormality, (2) quantitate its severity, and (3) locate the main site of disease (chest wall, alveoli or airways; generalised airway narrowing or localised obstruction of the central airway, etc.). Like tests of function of other organs, respiratory function tests should not be expected to be in themselves diagnostic. One obvious exception is asthma, but more often a pattern of abnormality suggests a particular pathogenetic mechanism and this directs attention to a related group of diseases, or the functional features may support other clinical and radiographic evidence and be consistent with a particular diagnosis. A set of lung function data should never be viewed in isolation, but the available clinical and radiographic data need also to be considered before formulating a report. Comments by the technician performing the tests are often revealing and helpful. For these reasons I personally am averse to computerised reporting, which usually amounts merely to a restatement of the numbers in words, without the all-important additional clinical comment or interpretation.