SPIROMETRY (LUNG FUNCTION TEST)

PRERNA FOR IAS

SPIROMETRY (LUNG FUNCTION TEST)

1. Spirometry (Lung Function Test)

Spirometry is a simple, non-invasive pulmonary function test used to measure how well the lungs work. It evaluates the amount of air a person can inhale and exhale, as well as the speed of airflow during breathing. The test helps diagnose and monitor respiratory diseases such as asthma, chronic obstructive pulmonary disease (COPD), pulmonary fibrosis, and other lung disorders. Spirometry is safe, painless, quick, and highly reliable when performed correctly. It is commonly used during routine respiratory evaluations, before surgery, and to assess the effectiveness of treatment. The results are displayed as graphs called spirograms.

2. How is Spirometry Done?

Spirometry is performed using a device called a spirometer. The patient sits comfortably and wears a nose clip to prevent air from escaping through the nose. After taking the deepest possible breath, the patient seals their lips tightly around the mouthpiece and exhales as forcefully and completely as possible. The spirometer records both the volume of air exhaled and the speed of exhalation. The procedure is usually repeated three times, and the best result is selected for analysis. Proper patient cooperation and correct technique are essential for obtaining accurate and reliable lung function measurements.

3. Important Spirometry Parameters

Spirometry measures several important lung volumes and capacities. Tidal Volume (TV) is the amount of air inhaled or exhaled during normal breathing. Inspiratory Reserve Volume (IRV) is the extra air inhaled after a normal inspiration, while Expiratory Reserve Volume (ERV) is the extra air exhaled after normal expiration. Residual Volume (RV) is the air remaining in the lungs after maximum exhalation. Vital Capacity (VC) is the maximum air exhaled after a deep breath. Forced Vital Capacity (FVC) and Forced Expiratory Volume in one second (FEV₁) are the most important measurements used clinically.

4. Spirogram

A spirogram is a graphical representation of lung volumes and airflow recorded during spirometry. It helps visualize normal and abnormal breathing patterns by plotting lung volume against time or airflow. The graph shows important parameters such as Tidal Volume (TV), Inspiratory Reserve Volume (IRV), Expiratory Reserve Volume (ERV), Residual Volume (RV), and Vital Capacity (VC). Doctors analyze the shape and values of the spirogram to identify obstructive or restrictive lung diseases. Changes in the graph help assess disease severity, monitor treatment response, and evaluate lung function before surgery or during routine respiratory examinations.

5. Obstructive Pattern

An obstructive spirometry pattern occurs when airflow through the airways is reduced due to narrowing or blockage. Conditions such as asthma, COPD, and emphysema commonly produce this pattern. The hallmark feature is a marked reduction in FEV₁ with a decreased FEV₁/FVC ratio, usually below 70%. Forced Vital Capacity (FVC) may remain normal or decrease slightly. Patients often have difficulty exhaling air quickly because of airway obstruction. Spirometry is valuable for diagnosing obstructive lung diseases, determining their severity, and monitoring improvement after bronchodilator therapy or other treatments.

6. Restrictive Pattern

A restrictive spirometry pattern occurs when the lungs cannot expand fully, reducing lung volumes. Diseases such as pulmonary fibrosis, pneumoconiosis, obesity-related restriction, and severe kyphoscoliosis commonly cause this pattern. The Forced Vital Capacity (FVC) is significantly reduced because lung expansion is limited. FEV₁ may also decrease, but the FEV₁/FVC ratio usually remains normal or increases because both values decrease proportionally. Patients often experience shortness of breath and reduced exercise tolerance. Spirometry helps identify restrictive lung disease, although additional tests such as full lung volume measurement are often needed for confirmation.

7. Mixed Pattern

A mixed spirometry pattern combines features of both obstructive and restrictive lung diseases. In this pattern, both FEV₁ and FVC are significantly reduced, and the FEV₁/FVC ratio is usually decreased. Mixed patterns occur in conditions such as advanced COPD with pulmonary fibrosis or asthma accompanied by restrictive lung disease. Patients often have severe breathing difficulty and reduced lung function. Additional investigations, including complete pulmonary function testing and imaging studies, may be required to determine the exact underlying cause. Identifying the mixed pattern helps doctors plan appropriate treatment strategies for complex respiratory disorders.

8. Normal Adult Spirometry Values

Normal spirometry values vary according to age, sex, height, and ethnicity, but standard adult reference values are commonly used. Forced Vital Capacity (FVC) normally ranges from 3.5 to 5.0 liters, while Forced Expiratory Volume in one second (FEV₁) ranges from 2.5 to 4.0 liters. The normal FEV₁/FVC ratio is approximately 75–85%. Values below the normal range may indicate lung disease. These reference values help physicians compare an individual's lung function with expected normal values and determine whether respiratory impairment is obstructive, restrictive, or mixed in nature.

9. Clinical Uses of Spirometry

Spirometry has many important clinical applications in respiratory medicine. It is used to diagnose obstructive lung diseases such as asthma and COPD, as well as restrictive lung diseases like pulmonary fibrosis. The test helps assess disease severity, monitor disease progression, and evaluate the effectiveness of treatment over time. Spirometry is also performed before major surgery to assess lung function and estimate surgical risk. Occupational health programs use spirometry to evaluate workers exposed to dust, chemicals, or pollutants. Regular spirometry helps detect early lung disease and supports timely medical intervention for better patient outcomes.

10. Key Points of Spirometry

Spirometry measures how much air a person can breathe in and out and how quickly the air is exhaled. The FEV₁/FVC ratio is the most important parameter for distinguishing obstructive from restrictive lung diseases. In obstructive disorders, airflow is reduced because of airway narrowing, whereas restrictive disorders result from reduced lung expansion. Spirometry is a safe, painless, rapid, and inexpensive diagnostic test that plays a vital role in respiratory medicine. It is widely used for diagnosis, monitoring treatment response, pre-operative evaluation, and occupational health assessments, making it an essential tool in clinical practice.