spirometry

Spirometry is a common pulmonary function test that measures how much air the lungs can hold and how quickly air can be exhaled. It is used to assess overall lung function, diagnose and monitor respiratory diseases, guide treatment decisions, and support preoperative or occupational health evaluations.

The test is performed with a spirometer. After a maximal inhalation, the patient exhales forcefully and as completely as possible into the device. The spirometer records a volume-time curve from which several indices are derived. The major measurements are forced vital capacity (FVC) and the forced expiratory volume in one second (FEV1). The FEV1/FVC ratio is also reported. Other outputs include peak expiratory flow (PEF) and flow rates at various percentages of FVC.

Interpretation centers on patterns of airflow limitation. Obstructive diseases, such as asthma and COPD, typically show reduced FEV1 and a lowered FEV1/FVC ratio. Restrictive conditions show reduced FVC with a normal or elevated FEV1/FVC ratio. Bronchodilator reversibility testing may be performed by repeating the test after inhaled bronchodilators; a significant increase in FEV1 (commonly ≥12% and ≥200 mL) supports a reversible component.

Quality and reference values are important. Acceptable tests require reproducible results, often with at least three maneuvers and two that meet criteria. Predicted values depend on age, height, sex, and ethnicity, and results are usually compared with lower limits of normal.

Limitations include that spirometry does not measure residual volume or total lung capacity and cannot assess diffusion capacity. Its accuracy depends on patient effort and technique, and it is typically complemented by full pulmonary function testing for a comprehensive evaluation.