Diagnosis and early detection of COPD using spirometry

Abstract

The standard respiratory function test for case detection of chronic obstructive pulmonary disease (COPD) is spirometry. The criterion for diagnosis defined in guidelines is based on the FEV1/FVC ratio forced expiratory ratio (FER) and its severity is based on forced expiratory volume in one second (FEV1) from measurements obtained during maximal forced expiratory manoeuvres. Spirometry is a safe and practical procedure, and when conducted by a trained operator using a spirometer that provides quality feedback, the majority of patients can be coached to provide acceptable and repeatable results. This allows potentially wide application of testing to improve recognition and diagnosis of COPD, such as for case finding in primary care. However, COPD remains substantially under diagnosed in primary care and a major reason for this is underuse of spirometry. The presence of symptoms is not a reliable indicator of disease and diagnosis is often delayed until more severe airflow obstruction is present. Early diagnosis is worthwhile, as it allows risk factors for COPD such as smoking to be addressed promptly and treatment optimised. Paradoxically, investigation of the patho-physiology in COPD has shown that extensive small airway disease exists before it is detectable with conventional spirometric indices, and methods to detect airway disease earlier using the flow-volume curve are discussed.

Keywords: Spirometry; case finding; chronic obstructive pulmonary disease (COPD); flow-volume curve.

Figure 1

Variables used to quantify global and peripheral concavity (see text). Measured FEF_50% and measured FEF_75% are the forced expired flows when 50% and 75% of the FVC has been expired. Reference FEF_50% and Reference FEF_75% are the reference flows that would be obtained if the flow-volume curve had zero curvature i.e., a linear descending limb (dotted line). The variable, y, is the volume to peak expiratory flow (PEF); a value of 0.6 L can be assumed for this. In this example, global concavity is approximately 50 Units and peripheral concavity is approximately 65 Units.

Figure 2

Post-bronchodilator forced expiratory ratio (FER) of FEV₁/FVC plotted against global and peripheral concavity in male participants. The horizontal and vertical lines are the limits of normal for FER (15) and concavity, respectively. The shaded quadrant identifies subjects with normal FER but an abnormal degree of concavity (see text).