Pulmonary Function Test

A Pulmonary Function Test (PFT) is a group of non-invasive breathing tests that measure how well your lungs take in air, hold it, and push it back out. The results give your doctor a detailed picture of your lung capacity and airflow, without any needles or cuts.

During the test, you breathe in and out through a mouthpiece connected to a machine called a spirometer (a device that records airflow and lung volume). The machine tracks how much air you can move, how fast you can move it, and how efficiently your lungs transfer oxygen into your blood. Some PFT packages also include a gas diffusion test, which checks how well the tiny air sacs in your lungs — called alveoli — pass oxygen across into your bloodstream.

Doctors order a Pulmonary Function Test when they need to understand the cause of breathing problems, monitor a known lung condition, or check lung health before a major operation. It is useful both for finding new diagnoses and for tracking how well treatment is working.

• Persistent cough, shortness of breath, or wheezing with no clear cause
• Suspected or confirmed asthma (a condition where the airways narrow and swell, making breathing difficult)
• Chronic Obstructive Pulmonary Disease — COPD — (a long-term lung disease that blocks airflow, usually caused by smoking)
• Pulmonary fibrosis (scarring of lung tissue that makes the lungs stiff)
• Occupational lung disease (lung damage caused by breathing in dust, chemicals, or fumes at work)
• Sarcoidosis (an inflammatory condition that can form clusters of inflamed cells in the lungs)
• Before surgery, especially heart or thoracic (chest) surgery, to assess how well the lungs can handle the stress
• Monitoring the effect of medications or therapies on lung function over time

There are a few situations where some parts of the PFT may not be suitable, or where the test needs to be postponed.

• Recent heart attack or unstable chest pain — the breathing effort can put strain on the heart
• Recent eye surgery — the pressure of blowing hard can temporarily raise pressure inside the eye
• Recent abdominal or chest surgery — forceful breathing can stress healing wounds
• Severe active respiratory infection — results may be unreliable and the test can spread infection
• Uncontrolled high blood pressure at the time of the test

A Pulmonary Function Test is one of the safest diagnostic procedures available — it involves only controlled breathing and carries no radiation, no needles, and no sedation. Serious complications are very rare.

• Temporary dizziness or light-headedness from breathing very hard or fast — this usually passes within a minute or two of resting
• Mild shortness of breath or chest tightness immediately after forceful exhalation, particularly in people with severe asthma — the team will monitor you and this resolves quickly
• Fatigue or headache after the session in some patients, especially those with poor baseline lung function
• In very rare cases, the forced breathing effort may trigger a bronchospasm (a sudden tightening of the airway muscles) in people with highly reactive airways — trained staff are present to manage this if it occurs
• Fainting is uncommon but possible if a patient holds their breath or strains excessively

Getting ready for a Pulmonary Function Test is straightforward, but following the instructions carefully helps ensure the results are accurate. Most preparations focus on avoiding things that can temporarily change your airflow before the test.

In the hours before the test, your doctor or clinic will usually advise the following:

• Avoid smoking for at least four to six hours before the test — smoke irritates and temporarily constricts (narrows) the airways
• Avoid heavy exercise for at least four hours beforehand, as this can alter normal breathing patterns
• Avoid large meals right before the test — a full stomach can restrict how deeply you can inhale
• Avoid alcohol for at least four hours before the test
• Wear loose, comfortable clothing that does not restrict your chest or abdomen
• Some inhaled medications (bronchodilators — medicines that open the airways) may need to be paused before the test so that the results reflect your natural lung function; your doctor will give specific guidance on this
• There is generally no fasting requirement for a standard PFT unless it is combined with another procedure

Before the main breathing tests, the healthcare team will usually carry out a few simple checks, such as measuring your height and weight (needed to calculate your predicted lung values), checking your blood pressure, and confirming your medical history and any current medications.

The test itself follows a series of steps. The exact number and order may vary slightly between hospitals and depending on which components your doctor has requested.

• 1. You will be seated in a chair, and a soft clip will be placed on your nose to ensure all air passes through the mouthpiece.
• 2. The technician will explain each breathing manoeuvre before you perform it, and will coach you through the effort with clear verbal instructions.
• 3. For spirometry (the most common component), you will breathe in as deeply as possible and then blow out as hard and fast as you can into the mouthpiece until your lungs feel completely empty.
• 4. This forceful exhalation is usually repeated several times to get consistent readings — the best results are used.
• 5. If a bronchodilator challenge is part of the test, you will inhale a medication to open your airways, wait a short period, and then repeat the spirometry to see if your lung function improves.
• 6. For lung volume measurement, you may be asked to sit inside a small, clear, sealed booth called a body plethysmograph (a cabin that measures air pressure changes to calculate total lung volume).
• 7. For the gas diffusion test, you will inhale a small, safe amount of tracer gas, hold your breath briefly, then exhale while the machine analyses how much gas crossed from your lungs into your blood.
• 8. The technician will review the results with you briefly and forward the full report to your referring doctor.

Because a Pulmonary Function Test involves no incisions, anaesthesia, or injections, recovery is immediate for most people. You can usually resume normal activities as soon as the appointment ends, unless your doctor gives different instructions based on your specific health situation.

• Most patients feel completely fine straight after the test; if you feel dizzy or short of breath, simply sit and rest in the clinic until it passes — the staff will check on you
• If a bronchodilator medication was used during the test, you may notice slightly faster breathing or a mild tremor (shaking) in your hands for a short time — this is normal and settles on its own
• You may eat, drink, and drive as normal after the test unless a short-term medication pause was advised and needs to be reversed carefully — your doctor will guide you
• Resume any inhaled or other medications that were paused before the test as advised by your doctor
• Your referring doctor will review the full report and discuss the results with you at a follow-up appointment — results are not usually interpreted at the test centre itself
• If the results suggest a new lung condition, or a significant change in a known condition, your doctor will discuss next steps, which may include further imaging such as a CT scan of the chest, additional blood tests, or adjustments to your treatment plan
• If your doctor monitors your lung condition over time, repeat PFTs are commonly done at regular intervals to track changes — the frequency depends on your condition and your doctor's judgement