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How can spirometry measure airflow obstruction in the lungs?

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Medical illustration of the human chest showing the lungs, diaphragm, ribs, trachea, bronchus, and bronchioles, with one lung cut away to reveal internal structures. — respiratory disease The bronchioles of the lungs are the site where oxygen is exchanged for carbon dioxide during the process of respiration. Inflammation, infection, or obstruction of the bronchioles is often associated with acute or chronic respiratory disease, including bronchiectasis, pneumonia, and lung abscesses.

Spirometry is a pulmonary function test used to assess the ventilation capacity of the lungs and quantify the degree of airflow obstruction.1

The procedure measures the rate and quantity of air that a patient exhales forcibly after taking a full, deep breath. By recording these breathing movements, often graphically on a spirogram, clinicians can derive specific metrics to identify obstructions:12

Forced Expiratory Volume (FEV): Measures the maximum volume of air that can be expelled from the lungs within a specific time interval.2
Maximal Expiratory Flow Rate (MEFR): Calculates the maximal flow rate of a single forced breath, expressed in litres per minute.2

These measurements allow healthcare providers to determine how efficiently the lungs move air in and out, helping to diagnose and monitor respiratory diseases characterized by airway narrowing or obstruction.21