Pulmonary Function Tests (PFT): Understanding the Procedures and Results

In the modern world, where increasing air pollution is resulting in an alarming increase in the cases of respiratory disorders, the significance of lung health cannot be overstated. According to the WHO, chronic respiratory disorders are among the leading causes of death globally, with COPD (Chronic Obstructive Pulmonary Disorder) alone causing 3.23 million deaths in 2019. The numbers, since then, have only increased. It is, therefore, extremely important to take care of your lungs and identify problems at an early stage, which brings us to pulmonary function tests. 

What are Pulmonary Function Tests?

Pulmonary function tests, commonly called “PFT tests”, is a collective term for a number of tests used to assess lung health. They are non-invasive tests and commonly used to diagnose, monitor, and manage respiratory conditions such as asthma, COPD, and other lung-related disorders. They can assess various aspects of lung performance, including air intake efficiency, oxygen absorption, and exhaling efficiency. 

What are the Types of Pulmonary Function Tests?

Various types of lung function tests assess different aspects of lung performance. Some of the most commonly used LFT tests include:

Spirometry

Spirometry is a commonly used PFT test designed to measure lung function. It evaluates two critical aspects:

1. The amount of air the lungs can inhale and exhale.
2. The speed at which air is exhaled.

During a spirometry test, the patient is asked to breathe into a mouthpiece which is connected to a spirometer - a device that records the volume and speed of air movement. The patient is asked to take a deep breath and then exhale with full force into the mouthpiece. After this, the patient may also be asked to breathe normally for a few cycles. This process may be repeated multiple times to ensure accuracy.

Body Plethysmography

Body plethysmography is a precise method used to determine the volumes of lungs, particularly when more detailed measurements are required. The test is performed in a sealed, transparent chamber (plethysmograph) and is particularly useful for evaluating the amount of air in the lungs, including volumes that cannot be measured by spirometry, such as residual volume (RV). 

During a body plethysmography test, the patient is asked to sit inside a sealed chamber and breathe through a mouthpiece, which changes the chamber’s pressure. The changes are recorded as the patient breathes normally and performs specific breathing exercises. The observations allow doctors to calculate the volumes of lungs and airflow resistance.

Gas Diffusion Study

A gas diffusion study is used to measure how effectively the lungs are able to transfer oxygen to the bloodstream and take carbon dioxide. This test provides critical insights into lung function, particularly the efficiency of the alveolar-capillary membrane - a vital structure in the lungs responsible for gas exchange and fluid balance.

During a gas diffusion study, the patient is asked to inhale a harmless tracer gas, such as carbon monoxide (CO), mixed with a small amount of helium or methane. Then the patient is asked to hold their breath for a few seconds before exhaling. The amount of gas exhaled is analysed to determine how much of it was absorbed by the blood while the patient held their breath.

Cardiopulmonary Exercise Test (CPET)

CPET is a comprehensive diagnostic test that evaluates how well the heart, lungs, and muscles work together during physical activity. It provides detailed insights into the body’s ability to perform sustained exercise and is used to assess the overall function of the cardiopulmonary system.

During a CPET test, the patient is asked to run on a treadmill or cycle a stationary bike, while connected to medical monitoring equipment that measure:

1. Oxygen uptake (VO₂)
2. Carbon dioxide output (VCO₂)
3. Breathing rate and volume
4. Heart rate and blood pressure

In addition, sensors and a face mask/mouthpiece are used to capture and analyse respiratory gases in real-time.

By providing an integrated view of how the heart, lungs, and muscles respond to stress, CPET offers precise insights that help doctors to tailor treatment plans, guide rehabilitation, and evaluate the prognosis in cases of chronic cardiopulmonary diseases.

Bronchial Provocation Test

The Bronchial Provocation Test is a specialised diagnostic procedure used to evaluate airway hyperresponsiveness (a state where the airways are more sensitive to stimuli that narrow them), which is a key characteristic of conditions such as asthma. The test involves exposing the airways to a controlled stimulus, such as methacholine, mannitol, or exercise, to induce bronchoconstriction (narrowing of the airways). The goal is to measure how reactive or sensitive the airways are to these stimuli.

During the test, the patient’s lung function is measured using spirometry to establish a baseline forced expiratory volume in one second (FEV₁). After that, a nebulizer is used to deliver a small, increasing dose of methacholine or other agents. After each dose, spirometry is repeated to evaluate changes in lung function. If the FEV₁ drops by 20% or more, it indicates airway hyperresponsiveness.

Exhaled Nitric Oxide Test

The Exhaled Nitric Oxide Test (FeNO test) is a non-invasive test used to measure the level of nitric oxide (NO) in exhaled breath, which serves as a marker of airway inflammation. Elevated NO levels indicate the presence of eosinophilic inflammation, which is commonly associated with respiratory conditions. The FeNO test is valuable for distinguishing asthma from other respiratory conditions such as COPD or non-inflammatory airway disorders.

Before the test, patients are instructed to avoid eating, drinking, smoking, or exercising for at least one hour before the test to ensure accurate results. During the procedure, the patient inhales deeply and then exhales slowly and steadily into a handheld device or analyzer. The device measures the concentration of nitric oxide in the breath, typically in parts per billion (ppb). Normal levels are generally below 25 ppb, and anything above that suggests airway inflammation.

Pulse Oximetry Test

The Pulse Oximetry Test is used to measure the oxygen saturation level (SpO₂) in the blood, which indicates how effectively oxygen is being delivered to the body. This test is widely used to monitor respiratory and cardiovascular health in conditions such as asthma, chronic obstructive pulmonary disease (COPD), pneumonia, and heart failure. It is particularly valuable for detecting hypoxemia (low blood oxygen levels) and assessing the need for supplemental oxygen therapy. 

The test involves placing a small device, called a pulse oximeter, on a body part such as a fingertip, earlobe, or toe. The device uses light sensors to measure oxygen saturation by analysing the colour and absorption of light through the blood. The patient is usually asked to remain still during the test to ensure accurate readings. Results are displayed within seconds, showing the oxygen saturation percentage and, in most cases, the heart rate. Normal oxygen saturation levels typically range between 95% and 100%.

Plethysmography Test

The Plethysmography Test is used to measure changes in volume within an organ or part of the body. In respiratory care, plethysmography is used to measure lung volumes, particularly in patients with conditions such as chronic obstructive pulmonary disease (COPD), asthma, or pulmonary fibrosis. By accurately measuring lung capacity and airway resistance, this test provides critical insights into pulmonary function and helps guide effective treatment strategies.

During the test, the patient performs various breathing manoeuvres, such as normal breathing, deep inhalations, or quick exhalations, as instructed by the technician. The machine measures changes in air pressure and airflow inside the booth caused by the patient’s breathing. These changes allow the system to calculate lung volumes, including residual volume (RV), functional residual capacity (FRC), and total lung capacity (TLC). 

Diffusion Capacity Test

The Diffusion Capacity Test (also called the DLCO test) is used to measure how well gases such as oxygen move from the lungs into the bloodstream. This test evaluates the efficiency of the alveoli, the tiny air sacs in the lungs where gas exchange occurs, and the surrounding capillaries. It is commonly performed to diagnose or monitor conditions that affect gas exchange, such as pulmonary fibrosis, emphysema, chronic obstructive pulmonary disease (COPD), and pulmonary hypertension. 

During the test, the patient is asked to exhale fully, inhale a harmless gas mixture (including carbon monoxide and a tracer gas), hold their breath for 10 seconds, and then exhale into a machine. The device analyses the exhaled air to determine how much carbon monoxide was absorbed, reflecting the lungs' gas exchange efficiency. Reduced diffusion capacity may indicate lung scarring, alveolar damage, or impaired blood flow. 

When is Pulmonary Function Testing Performed?

Pulmonary Function Testing is a cornerstone of respiratory medicine, essential for diagnosing, monitoring, and managing a wide range of lung diseases. It is commonly recommended in the following scenarios:

1. Diagnosing Respiratory Conditions

PFT is often the first step in identifying the cause of respiratory symptoms, such as coughing, wheezing, or breathlessness:

• Asthma: PFTs are used to measure airway responsiveness and detect reversible airflow obstruction. Tests such as spirometry and bronchial provocation are commonly used.
• Chronic Obstructive Pulmonary Disease (COPD): PFT is used to evaluate airflow limitation and lung capacity, distinguishing between chronic bronchitis and emphysema.
• Interstitial Lung Diseases: Conditions like pulmonary fibrosis are assessed through lung volumes and gas exchange efficiency, identifying reduced lung elasticity and scarring.
• Restrictive Lung Diseases: PFT helps determine whether decreased lung expansion results from conditions like obesity, neuromuscular diseases, or thoracic deformities.

2. Monitoring Disease Progression

PFT is critical in tracking the progression of chronic lung diseases over time:

• For asthma and COPD, regular tests are conducted to monitor worsening airflow limitation or changes in airway inflammation.
• In pulmonary fibrosis or other interstitial lung diseases, PFT helps in tracking increasing lung stiffness and declining gas exchange.

By monitoring these changes, clinicians can adjust treatment plans to slow disease progression and maintain the patient’s quality of life.

3. Evaluating Treatment Effectiveness

PFT helps determine how well a patient is responding to therapy:

• Bronchodilator Response: Spirometry can assess how inhaled medications improve airflow obstruction in asthma or COPD.
• Corticosteroid Therapy: Improvement in lung function or airway inflammation following treatment is often measured in conditions like asthma or eosinophilic bronchitis.
• Pulmonary Rehabilitation: PFT can evaluate lung function improvements after lifestyle changes or pulmonary rehabilitation programs.

4. Pre-Surgical Assessment

PFT is crucial before certain surgeries to minimise post-operative complications:

• Thoracic Surgery: For patients undergoing lung resections (e.g., for lung cancer), PFT determines if the remaining lung can handle the body's oxygen demands.
• Abdominal Surgery: In surgeries affecting the diaphragm or requiring prolonged anaesthesia, PFT ensures the patient has adequate respiratory reserve.
• Poor lung function results may lead to surgical modifications or postponements.

5. Exposure to Lung Irritants

PFT is used to assess individuals exposed to potentially harmful substances:

• Occupational Hazards: People working in industries like mining, construction, or manufacturing may develop diseases like asbestosis, silicosis, or occupational asthma.
• Environmental Hazards: Exposure to pollutants, smoke, or allergens may lead to lung damage, requiring regular PFT for early detection.

6. Unexplained Respiratory Symptoms

When patients present with persistent or unexplained symptoms, PFT helps narrow down potential causes:

• Chronic Cough: It could point to asthma, COPD, or interstitial lung disease.
• Shortness of Breath: PFT distinguishes between respiratory and non-respiratory causes, such as heart disease.
• Wheezing or Chest Tightness: It identifies conditions like asthma or hyperactive airway disorders.

By identifying the underlying cause, PFT ensures appropriate diagnostic testing and targeted treatment.

How to Interpret the Results of a Pulmonary Function Test?

Interpreting the results of a Pulmonary Function Test requires a detailed understanding of lung physiology and clinical expertise. While the results provide key metrics, such as lung volumes, airflow, and gas exchange efficiency, which can indicate normal lung function or reveal respiratory conditions, it is essential that the results are interpreted by a qualified doctor for accurate diagnosis and treatment planning. That’s because the interpretation of PFTs can vary significantly based on various factors such as age, sex, height, and medical history, and self-interpretation may only lead to misunderstanding or unnecessary concern.

Read more -Liver Function Tests: Purpose, Types & Interpretation

Final Words

If you have undergone a Pulmonary Function Test or are experiencing respiratory symptoms such as persistent coughing, shortness of breath, or wheezing, it’s crucial to seek expert medical advice. At Max Hospitals, our experienced pulmonologists specialise in using PFTs to provide personalised care for a wide range of respiratory conditions. With state-of-the-art facilities and a compassionate approach, we ensure you receive accurate diagnosis and effective treatment. Book a consultation with a pulmonologist at Max Hospitals today for comprehensive care.