Table 2.

Investigative modalities with potential for diagnosis of early COPD.

Spirometry	Useful in conjunction with other investigations but has potential to miss early disease
FEF 25–75%	Identifies small airway disease, which has been explored as site of initial development of pathology in COPD
DLCO	Identifies airway disease and emphysema prior to identification of disease on spirometry
Oscillometry	Has potential to identify small airway disease; however universally accepted standardisation of cut-off values required
HRCT	Identifies characteristic changes on lung parenchyma such as emphysema, air trapping and bronchial wall thickening in the absence of spirometry-defined airflow obstruction
PRM	Has potential to identify fSAD, which appears to precede development of emphysema

COPD, chronic obstructive pulmonary disease; DLCO, diffusion capacity for carbon monoxide; FEF, forced expiratory flow at 25–75% of forced vital capacity; fSAD, functional small airway disease; HRCT, high resolution computed tomography; PRM, parametric response mapping.