Pulmonary Function Test: Purpose, Procedure, and Risks

If your doctor has ordered a pulmonary function test (PFT), you might be imagining a lab coat, a mysterious machine, and someone yelling,
“BREATHE LIKE YOU MEAN IT!” (Okay, that last part is not totally wrong.)
The good news: PFTs are common, usually quick, and designed to answer a simple questionhow well are your lungs doing their job?

Think of a PFT as a “performance review” for your breathing system. It measures how much air you can move, how fast you can move it,
and how effectively oxygen gets from your lungs into your bloodstream. The results can help your clinician diagnose lung conditions,
track how a disease is changing over time, and see whether a treatment is actually helping (instead of just being emotionally supportive).

What a Pulmonary Function Test Measures

Pulmonary function tests are not one single test. They’re a family of breathing tests that look at different parts of lung function.
Depending on why you’re being tested, your appointment may include one testor a whole “lung function sampler platter.”

1) Airflow (How Easily Air Moves In and Out)

Airflow testing focuses on how quickly and forcefully you can exhale. This is where spirometry shines.
It’s especially useful for spotting airflow obstruction (when air has trouble getting out), which can happen in conditions like asthma or COPD.

2) Lung Volumes (How Much Air Your Lungs Can Hold)

Lung volume tests estimate the total amount of air in your lungs and how much remains after you exhale. These measurements can help identify
restrictive patterns (when lungs or chest mechanics limit expansion) and can also reveal “air trapping” in some obstructive diseases.

3) Gas Transfer (How Well Oxygen Crosses Into the Bloodstream)

Diffusion testingoften reported as DLCOestimates how efficiently gases move from the air sacs in your lungs into your blood.
This can be important when someone has shortness of breath but spirometry doesn’t tell the whole story.

4) Exercise Response (How Heart + Lungs + Muscles Work Together)

Some labs offer cardiopulmonary exercise testing (CPET), which measures how your body responds during controlled exercise.
It’s typically used when symptoms show up with activity and the cause isn’t obvious from resting tests.

Why Your Clinician Might Order a PFT

Pulmonary function testing is ordered for lots of real-life reasons, not just “mystery lung drama.” Common goals include diagnosing a condition,
measuring severity, monitoring changes over time, and checking how well treatments are working.

• Symptoms: shortness of breath, wheezing, chronic cough, chest tightness, or unexplained exercise intolerance.
• Diagnosis support: asthma, COPD, chronic bronchitis, emphysema, pulmonary fibrosis, and other lung disorders.
• Pre-surgery check: to estimate whether your lungs can tolerate anesthesia and recovery.
• Work or environmental exposures: to see whether certain exposures may be affecting lung function.
• Monitoring: tracking lung disease progression or response to medications.

A key point: PFTs don’t always diagnose one specific disease by themselves. Instead, they reveal patternslike obstructive or restrictive changes
that your clinician interprets alongside your history, exam, imaging, and sometimes lab work.

Types of Pulmonary Function Tests

Spirometry (The Most Common PFT)

Spirometry measures how much air you can breathe out and how quickly you can do it. You’ll inhale deeply and then blow out as hard and fast as you can,
following the technician’s coaching. It’s simple in conceptbut it does require effort and technique.

You’ll often see these spirometry values:

• FVC (Forced Vital Capacity): the total amount of air you can forcefully exhale after a full inhale.
• FEV1 (Forced Expiratory Volume in 1 second): how much air you can force out in the first second.
• FEV1/FVC ratio: helps identify obstruction when it’s low.

Sometimes spirometry is done before and after a bronchodilator (an inhaled medication that opens the airways).
If airflow improves meaningfully after the medication, that can suggest reversible airway narrowingoften seen in asthma.

Lung Volumes (Including Body Plethysmography)

Lung volume testing measures the total air in your lungs and how it’s distributed (for example, what’s left after you exhale).
One common method is body plethysmography, where you sit in a clear chamber (yes, it looks a bit like a phone booth)
and breathe through a mouthpiece while pressure changes help calculate lung volumes.

Lung volume results often include:

• TLC (Total Lung Capacity): total air your lungs hold after the deepest possible breath in.
• FRC (Functional Residual Capacity): air left in the lungs at the end of a normal exhale.
• RV (Residual Volume): air that remains after you exhale as much as you can.

If you’re prone to claustrophobia, tell the staff. They do this all day and have strategies to help. You won’t be the first person to say,
“This booth is giving me elevator feelings.”

Diffusion Capacity (DLCO)

DLCO testing estimates how well gases move from your lungs into your bloodstream. During the test, you breathe in a tiny, controlled amount of test gas,
hold your breath briefly, and then exhale. The equipment compares what went in versus what came out, which helps estimate transfer efficiency.

DLCO can be helpful when evaluating shortness of breath, emphysema, or suspected interstitial lung disease. It can also be used to monitor changes over time.

Challenge Testing (When “Normal” Spirometry Isn’t the End of the Story)

If symptoms strongly suggest asthma but baseline testing is normal, a clinician may order a bronchial provocation test (like a methacholine challenge)
to check airway hyperreactivity. These tests are more specialized, take longer, and require very specific medication instructions beforehand.

Cardiopulmonary Exercise Testing (CPET)

CPET is like a stress test that focuses on the entire oxygen-delivery chain: lungs, heart, circulation, and muscle use of oxygen.
You’ll exercise on a treadmill or bike while your breathing, oxygen levels, heart rate, and blood pressure are monitored.
It’s usually ordered when exertional symptoms are out of proportionor when the cause is unclear.

How to Prepare for a Pulmonary Function Test

Preparation matters because PFTs measure performanceand performance changes if you show up after a huge meal, three espressos, and a sprint through the parking lot.
Your lab will give you instructions, and you should follow those over any generic checklist. That said, these are common recommendations:

Before the Test: Typical Do’s and Don’ts

• Don’t eat a heavy meal right before testing. A full stomach can make deep breaths harder.
• Avoid smoking beforehand. Many labs advise no smoking for several hours before testing.
• Avoid caffeine if instructed. Some centers recommend skipping caffeine before the test.
• Skip heavy exercise beforehand. Arrive with your breathing as close to “baseline” as possible.
• Wear loose, comfortable clothing. You want your chest and belly to move freely.
• If you wear dentures, keep them in. They can help you seal your lips around the mouthpiece.

Medication Notes (Very Important)

Some inhalers (bronchodilators) can change your results. Depending on why the test is ordered, your clinician may want you to hold certain inhalers beforehand.
Other times, they may want you to keep taking your usual medications. The “right answer” depends on the clinical question.

Bottom line: do not stop any medication unless your healthcare team specifically tells you to.
If you’re unsure, call the ordering office or the pulmonary lab. A two-minute clarification can save you a rescheduled appointment.

When to Reschedule

If you have a respiratory infection (like a bad cold or the flu), or if you’re in the middle of a significant asthma flare,
you may be asked to postpone. Testing can be less accurate when you can’t give your best effortand some conditions make testing less safe.

What Happens During the Test

Most PFT appointments follow a predictable flow. The staff will guide you step-by-step, because “guessing” is not a reliable testing strategy.

Check-In and Setup

You’ll typically check in, review your medications, and have basic measurements recorded (like height and weight). Then the technician will explain each test.
You’ll wear nose clips and breathe through a mouthpiece so all airflow is measured accurately.

Spirometry: The “Big Blow” Part

1. You inhale as deeply as possible.
2. You seal your lips tightly around the mouthpiece.
3. You blast the air out hard and fast, then keep exhaling until told to stop.
4. You repeat several times to make sure the results are consistent.

The first attempt is often not the bestmost people improve with coaching. The technician may say things like “keep going, keep going!”
This is normal and not a personal commentary on your life choices.

Lung Volumes: The Clear Booth

If you’re doing body plethysmography, you’ll sit in a clear chamber. The door is closed briefly while you follow breathing instructions through the mouthpiece.
Some people feel fine; others feel a little boxed-in. If you’re uncomfortable, tell the staffyour comfort helps your performance, and your performance helps your data.

DLCO: The Breath-Hold Test

For diffusion testing, you’ll breathe normally, exhale, inhale a measured test gas, hold your breath for a few seconds, and then exhale.
The amount of gas exhaled helps estimate how efficiently gas exchange is happening.

Bronchodilator Testing

If your test includes “pre- and post-bronchodilator” measurements, you’ll take an inhaled medication during the visit and repeat spirometry after a short wait.
This helps show whether opening the airways changes airflow.

CPET or Other Walk/Exercise Tests

If exercise testing is included, you’ll be attached to monitors and exercise under supervision. The goal is controlled data, not a surprise audition for an action movie.

Understanding Your Results (Without Becoming a Pulmonologist Overnight)

PFT reports can look intimidating because they involve numbers, graphs, and percent predicted values. The most helpful mindset:
these results describe patterns. Your clinician interprets them in context.

Predicted Values, Percent Predicted, and “Normal”

Your results are compared with reference (“predicted”) values based on factors like age, height, and sex. Many labs now also use standardized approaches such as
z-scores to describe how far your result is from what’s expected for someone like you. Different labs may use slightly different reference equations,
so small differences between reports don’t automatically mean your lungs changed dramatically.

Common Pattern: Obstruction

Obstructive patterns generally mean air has trouble flowing out of the lungs. A classic clue is a lower FEV1/FVC ratio.
Examples of obstructive diseases include asthma, chronic bronchitis, and emphysema.

Example: Someone with wheezing and episodic symptoms might show reduced airflow on spirometry,
then improve after bronchodilator medication. That improvement can support a diagnosis involving reversible airway narrowing.

Common Pattern: Restriction

Restrictive patterns involve reduced lung expansion or reduced total lung capacity. In restrictive disease, FVC may be reduced,
and lung volume testing (like TLC) often helps confirm true restriction. Restriction can occur with interstitial lung disease, scarring,
certain chest wall conditions, and sometimes with severe obesity or neuromuscular weakness.

DLCO Clues

DLCO can provide extra information when spirometry doesn’t fully explain symptoms. For example:

• Low DLCO may be seen in emphysema or interstitial lung diseases (among other causes).
• Normal DLCO with obstructive spirometry may be seen in some asthma patterns.

These are not absolute rulesjust common clinical “tells” that help guide diagnosis and next steps.

Risks, Side Effects, and When Testing May Be Postponed

The vast majority of people complete PFTs without serious problems. These are noninvasive tests, and the most common issues are temporary and manageable.
Still, it’s smart to know what can happen.

Common (Usually Mild) Side Effects

• Lightheadedness or dizziness: repeated deep breaths and forceful exhaling can trigger this.
• Coughing: especially during forced exhalation.
• Shortness of breath: briefly during or after effort-heavy maneuvers.
• Claustrophobia: sometimes during lung volume testing in the booth.

Less Common but Important Risks

In certain peopleespecially those with specific underlying lung diseasethere may be a small risk of complications such as a collapsed lung (pneumothorax).
Your clinician and the lab staff weigh these risks against the benefit of testing.

When You Might Not Be Tested (or Testing Might Be Delayed)

PFTs require effort and can temporarily increase pressures in the chest and abdomen during forced maneuvers. Because of that, testing may be postponed
or performed with extra caution if you have certain conditionsespecially if they are recent or unstable. Examples include:

• Recent heart attack or unstable heart condition
• Recent chest or abdominal surgery
• Recent eye surgery (pressure changes can be a concern)
• A known aneurysm (in the chest, belly, or brain), depending on size and clinical stability
• Active tuberculosis or a significant respiratory infection

Always tell the lab about recent surgeries, chest pain, fainting episodes with hard coughing/blowing, severe uncontrolled blood pressure,
or recent respiratory illness. The goal is not to cancel your test for fun. The goal is to get accurate information safely.

Practical Tips for Getting the Best, Most Accurate Results

• Ask what the test is trying to answer. “Diagnosis?” “Severity?” “Medication response?” The goal affects prep instructions.
• Seal your lips tightly. Air leaks can throw off results.
• Give maximal effortmultiple times. Consistency is part of what makes the test reliable.
• Speak up if you feel unwell. Dizziness, chest pain, severe shortness of breath, or anxiety are reasons to pause.
• Bring your medication list. Especially inhalers, doses, and when you last used them.

Real-World Experiences: What People Commonly Notice (About )

Medical descriptions of pulmonary function tests are accurate, but they’re also a little… sterile. Real people tend to describe PFTs in human terms:
“It was weirder than it was scary,” “I didn’t realize how much technique mattered,” or “I thought I was done, and then they said, ‘One more time.’”
If you’re wondering what the experience feels like, you’re not alonemost first-timers have the same questions.

The most common surprise is how coached the test is. You’re not expected to know what to do. The technician will cue you through each breath:
big inhale, tight seal, blast out, keep going, keep going, keep going. People often laugh afterward because it feels like a breathing pep rally.
And if your first attempt is messy (air leak, early stop, weak start), that’s normal. Many people get their best results on attempt two or three.

Another frequent comment is, “I got a little lightheaded.” That’s not a sign you failedit’s a sign you did repeated deep breathing and forceful exhaling,
which can temporarily change oxygen and carbon dioxide balance or simply make you dizzy from effort. Most labs will have you sit, rest, and repeat only when
you’re ready. People also mention coughingespecially if they already have airway irritation. It can feel ironic to cough during a test designed to measure
breathing, but coughing is a common part of the process, and staff expect it.

For the lung volume booth, experiences vary wildly. Some people feel totally fine and treat it like sitting in a fancy aquarium.
Others feel the “closed door” moment in their nervous system. A helpful trick many patients share is to focus on the technician’s voice,
keep your eyes on a stable point, and remind yourself the door can be opened quickly if needed. It also helps to mention claustrophobia up front,
because staff can explain the timing and steps more thoroughlyknowing what’s next reduces anxiety for many people.

Patients who do DLCO often say the test gas part sounds alarming until it’s explained. The test uses very small, controlled amounts,
and the breathing pattern is simple: inhale, hold, exhale. People frequently describe it as “like a brief yoga breath hold, but with nose clips.”
CPET or treadmill tests, on the other hand, tend to feel like a structured workout with lots of monitorsmore intense, but also more straightforward:
you walk or pedal, they measure, you stop when the protocol ends or you reach your limit.

Finally, many people walk away appreciating that PFTs can turn vague symptoms into measurable data. If you’ve been feeling winded, it can be validating
to have numbers that help explain whyor reassuring to see that lung function is stronger than you feared. Either way, the “experience” of a PFT is usually
less about pain and more about effort, coaching, and the oddly satisfying feeling of doing something practical for your health in under an hour.

Conclusion

Pulmonary function tests are one of the most useful ways to measure how your lungs are workingairflow, lung volumes, gas exchange, and sometimes exercise performance.
The tests are typically safe and noninvasive, and the biggest challenge for most people is simply giving consistent effort while following directions.
If you’re preparing for a PFT, follow the lab’s instructions closely, ask questions about medication timing, and speak up if you feel dizzy or uncomfortable.
Your lungs are doing the workyour job is just to show up and blow (accurately).