Learn about spirometry, lung volume tests, and diffusion capacity. Understand how PFTs help diagnose asthma, COPD, and other respiratory conditions.
By Dr. Ram Narayan Shah · Published June 2026 · 8 min read
Editorial note: general health information; seek professional assessment for personal medical decisions.
Pulmonary function tests (PFTs) are a group of non-invasive breathing tests that measure how well the lungs are working. They help diagnose and monitor respiratory conditions.
Spirometry is the most common PFT. It measures how much air you can inhale and exhale and how quickly you can exhale. You breathe into a mouthpiece connected to a spirometer.
Forced vital capacity (FVC) is the total amount of air you can forcefully exhale after taking the deepest breath possible. Reduced FVC indicates restrictive lung disease.
Forced expiratory volume in one second (FEV1) measures how much air you can exhale in the first second. A low FEV1 relative to FVC indicates obstructive lung disease like asthma or COPD.
The FEV1/FVC ratio helps distinguish obstructive from restrictive lung diseases. A ratio below 0.7 is characteristic of obstructive conditions.
Lung volume tests measure total lung capacity, residual volume, and other volumes that cannot be measured by spirometry alone. Body plethysmography is commonly used for this.
Diffusion capacity testing measures how well oxygen passes from the lungs into the bloodstream. Reduced diffusion capacity occurs in conditions affecting the lung tissue.
Bronchodilator response testing involves repeat spirometry after inhaling a bronchodilator medication. Significant improvement suggests reversible airway obstruction typical of asthma.
Peak expiratory flow monitoring measures the fastest speed you can exhale air. Home monitoring with a peak flow meter helps track asthma control over time.
PFTs are used to diagnose conditions like asthma, chronic obstructive pulmonary disease, pulmonary fibrosis, and sarcoidosis. They also assess lung function before surgery.
Preparation for PFTs includes avoiding heavy meals, smoking, and bronchodilator medications before testing. Wear loose clothing and inform your provider about any medications.
Using this guide safely
Learn about spirometry, lung volume tests, and diffusion capacity. Understand how PFTs help diagnose asthma, COPD, and other respiratory conditions. This article gives general context for a conversation with a qualified clinician; it is not a diagnosis, prescription, or personal treatment plan. Screening, testing, medicines, and lifestyle advice should be matched to age, symptoms, pregnancy status, medical history, medicines, and local availability.
How a clinician may assess the concern
A clinician would usually check what changed, when it began, what makes it better or worse, relevant diagnoses, medicines and supplements, allergies, family history, and previous results. The goal is to decide whether self-care, routine review, testing, referral, or urgent care is the safest next step.
Questions worth asking
- What are the likely explanations and important alternatives?
- Is a test, medicine, or procedure needed now, and what would it change?
- What are the benefits, limitations, risks, costs, and consequences of waiting?
- Which warning signs need urgent care, and when should progress be reviewed?
Results, follow-up, and local access
Ask who will explain a result or review the response to treatment, how long follow-up usually takes, and what to do if the plan does not help. In Nepal, availability, cost, language, travel distance, and access to a qualified clinician may affect the best next step. Keep copies of reports and use them during follow-up rather than repeating information from memory.
When to seek professional advice
Seek emergency care for severe breathlessness, blue lips, confusion, chest pain, coughing blood, or oxygen-related emergency concerns.
Preparing for a consultation
Bring inhalers, oxygen readings if available, prior reports, medicines, and a description of symptom triggers.
Common questions
What does this article cover?
Learn about spirometry, lung volume tests, and diffusion capacity. Understand how PFTs help diagnose asthma, COPD, and other respiratory conditions. It is general health information and does not diagnose an individual condition.
When should I contact a health professional?
Seek emergency care for severe breathlessness, blue lips, confusion, chest pain, coughing blood, or oxygen-related emergency concerns. For urgent symptoms or safety concerns, use emergency or urgent-care services rather than waiting for a routine appointment.
How should I use this information before an appointment?
Bring inhalers, oxygen readings if available, prior reports, medicines, and a description of symptom triggers.
Category: Respiratory
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