Pulmonary Function Test (PFT): Meaning, Equipment Used, Procedure, and Normal Values

What Is a Pulmonary Function Test (PFT)?

A Pulmonary Function Test (PFT) is a group of specialized respiratory diagnostic tests that evaluate how well the lungs function. These tests assess:

• The amount of air the lungs can hold
• The speed at which air can be inhaled and exhaled
• The efficiency of oxygen transfer from lungs to bloodstream

Unlike imaging tests such as chest X-rays or CT scans that show lung structure, PFTs measure lung performance, making them essential for functional assessment of the respiratory system.

Pulmonary Function Tests are:

• Non-invasive
• Painless
• Radiation-free
• Safe for repeated use

They are routinely performed in hospitals, diagnostic centers, pulmonology clinics, ICUs, and occupational health facilities.

Why Pulmonary Function Tests Are Clinically Important

Many lung diseases develop slowly and silently, showing symptoms only when significant lung damage has already occurred. PFTs allow early detection, accurate diagnosis, and ongoing monitoring of respiratory disorders.

Key Clinical Benefits of PFT Testing

• Early identification of lung disease
• Differentiation between obstructive vs restrictive lung disorders
• Monitoring progression of chronic respiratory conditions
• Assessing response to inhalers and medications
• Pre-operative respiratory fitness evaluation
• Occupational lung disease screening
• Long-term monitoring in smokers and ex-smokers

In India, PFTs are increasingly recommended due to urban pollution, industrial exposure, biomass fuel usage, and post-COVID respiratory issues.

Who Should Undergo a Pulmonary Function Test?

A Pulmonary Function Test is advised for individuals experiencing:

• Chronic cough
• Shortness of breath (dyspnea)
• Wheezing
• Chest tightness
• Reduced exercise tolerance
• Frequent respiratory infections

High-Risk Groups Who Should Regularly Do PFTs

• Asthma patients
• COPD patients
• Smokers and former smokers
• Industrial workers (cement, mining, chemicals, textiles)
• Traffic police and outdoor workers
• Post-COVID patients with breathlessness
• Pre-surgical patients

Types of Pulmonary Function Tests

Pulmonary Function Testing is not a single test-it is a set of complementary tests, each evaluating a specific aspect of lung function.

1. Spirometry Test

Spirometry is the most commonly performed PFT and forms the foundation of pulmonary diagnostics.

It measures:

• Forced Vital Capacity (FVC)
• Forced Expiratory Volume in 1 second (FEV₁)
• FEV₁/FVC ratio
• Peak Expiratory Flow Rate (PEFR)

Spirometry is essential for diagnosing:

• Asthma
• Chronic Obstructive Pulmonary Disease (COPD)
• Chronic bronchitis
• Emphysema

2. Lung Volume Tests

Lung volume testing measures:

• Total Lung Capacity (TLC)
• Residual Volume (RV)
• Functional Residual Capacity (FRC)

These tests help diagnose restrictive lung diseases.

3. Diffusion Capacity Test (DLCO)

The Diffusing Capacity of the Lung for Carbon Monoxide (DLCO) test evaluates how efficiently oxygen passes from the lungs into the blood.

Used in diagnosing:

• Pulmonary fibrosis
• Interstitial lung disease
• Pulmonary hypertension
• Emphysema

4. Bronchodilator Reversibility Test

This test evaluates how lung function improves after administering a bronchodilator, helping differentiate asthma from COPD.

5. Peak Flow Measurement

A Peak Flow Meter measures maximum airflow during forced expiration and is commonly used for:

• Home asthma monitoring
• Daily lung function tracking

Pulmonary Function Test Equipment Used

Accurate diagnosis depends on high-quality pulmonary diagnostic equipment.

1. Spirometry Machine

A spirometer is the core device used in PFT testing.

It measures:

• Airflow rate
• Lung volume
• Breathing patterns

Types of Spirometers

• Portable spirometer
• Desktop spirometer
• Computer-based spirometer
• Turbine spirometer
• Ultrasonic spirometer

2. Body Plethysmograph

A closed chamber used to measure:

• Lung volumes
• Airway resistance

Primarily used in advanced pulmonary laboratories and tertiary hospitals.

3. DLCO Analyzer

Used for:

• Gas diffusion assessment
• Advanced pulmonary diagnostics

4. Peak Flow Meter

A compact handheld device ideal for:

• Asthma patients
• Home respiratory care

5. Disposable Mouthpieces & Filters

Essential for:

• Infection control
• Accurate test results
• Patient safety

Pulmonary Function Test Procedure (Step-by-Step)

Before the Test

Patients should:

• Avoid smoking for 4–6 hours
• Avoid heavy meals
• Avoid strenuous exercise
• Wear loose, comfortable clothing

During the Test

1. Patient sits upright
2. Nose clip is applied
3. Mouthpiece is sealed with lips
4. Deep inhalation followed by forceful exhalation
5. Test repeated 2–3 times for accuracy
6. Bronchodilator administered if required

After the Test

• Patient resumes normal activity
• Results interpreted by pulmonologist

Pulmonary Function Test Normal Values

Normal PFT values depend on:

• Age
• Gender
• Height
• Ethnicity

Reference Normal Ranges

Interpretation of PFT Results

Obstructive Lung Disease

Seen in asthma and COPD

• Low FEV₁
• Reduced FEV₁/FVC ratio

Restrictive Lung Disease

Seen in pulmonary fibrosis

• Reduced lung volumes
• Normal FEV₁/FVC ratio

Mixed Pattern

Combination of both obstructive and restrictive features.

Pulmonary Function Test Cost in India

Benefits of Pulmonary Function Tests

• Early disease detection
• Non-invasive & painless
• Safe for children and elderly
• Monitors treatment effectiveness
• Essential for occupational health

Pulmonary Function Test in Children

Children above 5 years can safely undergo PFTs using paediatric spirometers designed for smaller lung volumes.

Home vs Diagnostic Lab PFT Testing

Conclusion

Pulmonary Function Tests are essential diagnostic tools for evaluating lung health, diagnosing respiratory disorders, and monitoring treatment outcomes. In a country like India, where respiratory risks are increasing, timely PFT testing can significantly improve quality of life and long-term health outcomes.

At Aarogyaa Bharat, we support accurate respiratory diagnostics by promoting reliable pulmonary equipment, patient education, and evidence-based healthcare solutions.