Understanding Spirometry & PFT Results: FVC, FEV1, and LLN Explained

What is a Pulmonary Function Test (PFT)?

A Pulmonary Function Test (PFT) is a non-invasive diagnostic test that measures how efficiently your lungs take in air, move air out, and deliver oxygen into your bloodstream. Spirometry is the most fundamental diagnostic component of PFT testing.

Key Spirometry Metrics

When reading a spirometry report, three primary numbers dictate the evaluation:

1. Forced Vital Capacity (FVC): The maximum volume of air you can forcefully exhale after taking the deepest breath possible (measured in Liters). 2. Forced Expiratory Volume in 1 Second (FEV1): The volume of air exhaled during the first second of maximal forced expiration. 3. FEV1/FVC Ratio: The percentage of your total vital capacity exhaled in the first second.

Reference Predicted Values & Biological Variation

Lung capacity varies naturally based on three primary demographic variables: - Biological Sex: Males typically have larger average lung volumes than females of equal height. - Height: Taller individuals have larger chest cavities and larger lung volumes. - Age: Lung elasticity naturally peaks in early adulthood and gradually decreases with age.

Obstructive vs. Restrictive Impairment Patterns

- Obstructive Defect: Characterized by an FEV1/FVC ratio below the Lower Limit of Normal (LLN) or below 70%. Common causes include asthma, COPD, and bronchitis. - Restrictive Defect: Characterized by a reduced FVC (under 80% predicted) while maintaining a normal FEV1/FVC ratio. Common causes include pulmonary fibrosis and chest wall constraints.

*Always discuss your spirometry test results with a board-certified pulmonologist.*