Pulmonary Function Test for Asthma: Types, Procedure & Results

Asthma is a chronic respiratory condition affecting over 262 million people worldwide, according to the World Health Organization (WHO). Diagnosing and managing asthma effectively requires accurate testing, and one of the most critical diagnostic tools is the Pulmonary Function Test (PFT).

In this article, we’ll explore the different types of pulmonary function tests for asthma, how they work, what to expect during the test, and how to interpret the results.

What Is a Pulmonary Function Test (PFT)?

A Pulmonary Function Test (PFT) is a group of non-invasive tests that measure how well your lungs work. These tests evaluate lung capacity, airflow, and gas exchange, which are crucial in diagnosing and monitoring asthma, COPD, and other respiratory conditions.

PFTs are essential in determining the severity of asthma, assessing response to treatment, and tracking disease progression over time.

Types of Pulmonary Function Tests for Asthma

There are several types of pulmonary function tests used to diagnose and monitor asthma. The most common ones include:

1. Spirometry

Spirometry is the gold standard test for asthma diagnosis. It measures the amount of air you can inhale and exhale and how quickly you can do so.

• How It Works: You breathe into a mouthpiece connected to a spirometer, which records your lung function. You may be asked to repeat the test after using a bronchodilator (asthma medication) to see if lung function improves.

• Key Measurements:

  • Forced Expiratory Volume in 1 second (FEV1): Measures how much air you can exhale in one second.

  • Forced Vital Capacity (FVC): Measures total air exhaled after taking a deep breath.

  • FEV1/FVC Ratio: Used to determine airflow obstruction.

• Normal Range: FEV1 of 80% or higher is considered normal, while lower values indicate airway obstruction.

2. Peak Flow Test

This simple, handheld test measures how fast you can blow air out of your lungs.

• How It Works: You blow forcefully into a peak flow meter, which gives a reading in liters per minute.

• Why It Matters:

  • Helps track daily asthma control.

  • Can detect early signs of an asthma flare-up.

• Normal Range: Varies based on age, height, and sex. A 20% drop from your normal peak flow rate indicates worsening asthma.

3. Methacholine Challenge Test

Used when spirometry results are inconclusive, this test assesses airway hyperresponsiveness.

• How It Works: You inhale increasing doses of methacholine, a substance that causes airway narrowing in people with asthma.

• Positive Test: If your lung function (FEV1) drops by 20% or more, it confirms airway sensitivity and supports an asthma diagnosis.

4. Bronchodilator Reversibility Test

This test is a variation of spirometry but includes the use of a bronchodilator (like albuterol) to determine how much lung function improves after medication.

• Positive Result: If FEV1 increases by 12% or more after using the bronchodilator, asthma is likely.

5. FeNO Test (Fractional Exhaled Nitric Oxide)

This test measures the level of nitric oxide in your breath, which indicates airway inflammation.

• How It Works: You exhale into a device that analyzes nitric oxide levels.

• Why It’s Useful: High nitric oxide levels suggest eosinophilic inflammation, commonly seen in allergic asthma.

6. Plethysmography (Lung Volume Test)

This test measures total lung volume and is useful in differentiating asthma from other lung diseases.

• How It Works: You sit inside a sealed chamber and breathe into a mouthpiece.

• Why It Matters: Helps assess trapped air in the lungs, common in severe asthma cases.

What to Expect During a Pulmonary Function Test

• Preparation: Avoid smoking, caffeine, and heavy meals before the test.

• Procedure: Depending on the test, you may breathe into a spirometer, use an inhaler, or inhale a substance like methacholine.

• Duration: Tests typically take 30-60 minutes.

• Possible Side Effects: Mild dizziness, coughing, or temporary shortness of breath.

How to Interpret Pulmonary Function Test Results

• Normal Results: Indicate healthy lung function with no airway obstruction.

• Obstructive Pattern (Seen in Asthma):

  • Low FEV1/FVC ratio (below 70%) suggests airflow limitation.

  • Significant improvement in FEV1 after a bronchodilator confirms reversible airway obstruction (a hallmark of asthma).

• Restrictive Pattern: Seen in lung diseases like pulmonary fibrosis, but not typically in asthma.

• Peak Flow Readings: Fluctuations of 20% or more indicate poorly controlled asthma.

Why Pulmonary Function Tests Are Crucial for Asthma Management

• Early Diagnosis: Helps detect asthma before symptoms become severe.

• Personalized Treatment: Guides medication adjustments for better control.

• Monitoring Progress: Tracks lung function changes over time.

• Preventing Exacerbations: Identifies worsening symptoms before a full-blown attack occurs.

Final Thoughts

Pulmonary function tests for asthma are essential for accurate diagnosis, treatment, and long-term management. Whether you're experiencing symptoms or need to track your condition, these tests provide critical insights into your lung health.

If you suspect you have asthma or need to optimize your current treatment plan, consult a pulmonologist to determine which pulmonary function test is best for you.