Pulmonary Function Tests: Spirometry – Principles and Interpretation

Spirometry is a fundamental pulmonary function test used to evaluate respiratory function by measuring the volume and flow of air inhaled and exhaled.

Introduction

Respiratory health is assessed using pulmonary function tests (PFTs), with spirometry being the most widely used. This test aids in diagnosing conditions like asthma, COPD, and restrictive lung diseases.

Principles of Spirometry

The test requires a patient to exhale forcefully into a spirometer, which records various metrics that help assess lung function.

• Forced Vital Capacity (FVC): The total volume of air expelled forcefully after full inhalation.
• Forced Expiratory Volume in 1 Second (FEV1): The volume of air exhaled in the first second, critical in evaluating airway obstruction.
• FEV1/FVC Ratio: Helps differentiate between obstructive and restrictive lung diseases.

Interpretation of Spirometry Results

Obstructive Lung Disease

Conditions such as asthma and COPD result in decreased FEV1/FVC ratio due to airflow limitation.

Restrictive Lung Disease

Diseases like pulmonary fibrosis lead to reduced FVC but a normal or slightly increased FEV1/FVC ratio.

Clinical Applications

Spirometry is used for diagnosing, monitoring, and assessing treatment efficacy for respiratory diseases.

Conclusion

Spirometry is a powerful tool for evaluating lung function, enabling early diagnosis and effective management of respiratory conditions.