What Happens During a Pulmonary Function Test? A Complete Patient Guide to Lung Health

Hearing that you need a pulmonary function test (PFT) might sound technical and intimidating, but these non-invasive assessments are the most effective way for Board Certified specialists to understand exactly how your lungs are working. At Muir Pulmonary Critical Care and Sleep Medicine, we believe that an informed patient is a relaxed patient. When you understand the 'why' and the 'how' behind a diagnostic procedure, the experience becomes a collaborative step toward better health rather than a source of anxiety.

Shortness of breath, a chronic cough, or wheezing can stem from a variety of causes, some related to the heart and others to the lungs. A PFT is essentially the gold standard for narrowing down these causes. We are here to demystify the process so you can walk into our Walnut Creek office feeling prepared and reassured about the care you are receiving.

Defining the PFT: It Is More Than Just One Test

Pulmonary function tests are not a single procedure but a group of non-invasive tests that measure lung volume, capacity, flow rates, and gas exchange. Together, these metrics build a complete picture of your respiratory health. Think of PFTs as a "roadmap" for your lungs. Just as a GPS determines your location and plans a route, a PFT determines the current status of your respiratory system and helps your doctor plan the most effective route for treatment.

According to the American Lung Association, these tests are critical for checking how well your lungs are working, especially if you have symptoms or risk factors for conditions like COPD, pulmonary fibrosis, or asthma. At Muir Pulmonary, we use these tests to determine if shortness of breath is caused by the lungs, the heart, or other physiological factors. Because the tests are safe and painless, they are an ideal first step in a diagnostic journey. No tools or instruments are placed inside your body; instead, the technology focuses on the air you move in and out.

The Diagnosis Comparison: Obstructive vs. Restrictive Lung Disease

One of the primary goals of pulmonary function testing is to categorize lung dysfunction into one of two main categories: obstructive or restrictive. Understanding the difference between these two is vital because the treatments for each are vastly different. Using a PFT to distinguish between them ensures you are not treated for asthma when you actually have a restrictive issue like pulmonary fibrosis.

Quick Verdict: At-a-Glance Comparison

Feature	Obstructive Lung Disease	Restrictive Lung Disease
Core Problem	Difficulty getting air out	Difficulty getting air in
Airway Status	Narrowed or blocked airways	Stiff lung tissue or chest wall
Key Metric	Decreased flow rates (FEV1)	Decreased lung volumes (TLC)
Common Examples	Asthma, COPD, Emphysema	Pulmonary Fibrosis, Sarcoidosis
PFT Result	Low FEV1/FVC ratio	Reduced Total Lung Capacity

Obstructive Lung Disease: The Challenge of Exhalation

In obstructive lung disease, the airways are narrowed, making it difficult for air to flow out of the lungs as quickly as it should. This creates airway resistance. Imagine trying to breathe out through a narrow straw; while you can eventually get the air out, it takes much more effort and time. Conditions like asthma, chronic bronchitis, and emphysema (the two main types of COPD) fall into this category. During a PFT, we measure how much air you can blow out in the first second of a hard breath (FEV1) to see if an obstruction exists.

Restrictive Lung Disease: The Challenge of Expansion

Restrictive lung disease occurs when the lung tissue itself becomes stiff or when the chest muscles and rib cage cannot expand fully. In this case, the lungs cannot hold the normal volume of air. It is not a matter of the air being blocked on its way out, but rather that the 'container'—your lungs—simply cannot get big enough to take in a full breath. Conditions like pulmonary fibrosis or even extreme obesity can cause restrictive patterns. PFTs measure the total lung capacity to identify if the volume is significantly lower than expected for your demographic.

The Patient Experience: What Actually Happens During the Exam?

A complete PFT at Muir Pulmonary typically consists of three main components. While you may only need one or two depending on your symptoms, many patients undergo all three to provide our Board Certified pulmonologists with the most comprehensive data set possible.

1. Spirometry: The Test of Effort

Spirometry is the most common PFT. You will be asked to sit upright and wear a nose clip to ensure all air travels through your mouth. You will then take the deepest breath possible and blow into a mouthpiece as hard and as fast as you can. This is often called a "maximal effort" test. It is not a casual breath; the technician will coach you to keep blowing until your lungs feel empty. This measures both the total amount of air you can exhale (FVC) and how much comes out in that critical first second (FEV1).

2. Plethysmography: The "Telephone Booth"

Body plethysmography is used to measure your total lung volume, including the air that stays in your lungs after you breathe out completely (residual volume). For this test, you will sit inside an airtight, clear box that looks somewhat like a modern telephone booth. While inside, you will perform small panting breaths against a shutter that opens and closes. By measuring the pressure changes inside the box versus the pressure at your mouth, we can calculate the exact volume of air your lungs can hold. This is the most accurate way to diagnose restrictive lung diseases.

3. Diffusion Studies (DLCO): Measuring Gas Exchange

It is not enough to know how much air you move; we also need to know if the oxygen is actually getting into your bloodstream. During a diffusion study, you will inhale a tiny, harmless amount of a tracer gas, hold your breath for about 10 seconds, and then blow it out. By analyzing the concentration of the gas you exhaled, we can determine how efficiently your lungs transfer oxygen from the air sacs (alveoli) into the small blood vessels (capillaries) surrounding them. This is vital for detecting early-stage emphysema or interstitial lung disease.

Preparation and Results: Getting the Most Accurate Data

To ensure that the data we collect is a true reflection of your lung health, specific preparation is required. Because PFTs require physical effort, your body needs to be in a neutral state.

How to Prepare

• Clothing: Wear loose-fitting, comfortable clothing that does not restrict your chest or abdomen. Athletic shoes are recommended as you may be asked to perform multiple rounds of breathing.
• Diet: Avoid large meals for at least two hours prior to the test. A full stomach can prevent your diaphragm from descending fully, which might skew your lung volume results.
• Substances: Do not smoke for at least six hours before the test. Smoking causes immediate airway irritation and can artificially alter your results. Additionally, avoid alcohol for at least eight hours prior.
• Medications: This is the most important step. Some quick-relief inhalers (bronchodilators) may need to be paused for 6 to 8 hours before the test so they do not 'mask' the underlying condition we are trying to diagnose. However, never stop taking daily maintenance medications unless specifically instructed by our office.

Understanding the Results

Once the testing is complete, your results are compared to "predicted values." These values are calculated based on your age, height, gender, and ethnicity—factors that naturally determine lung size and function.

At Muir Pulmonary, the unique value we provide lies in the interpretation. While a machine generates the numbers, our Board Certified specialists look at the nuances. We distinguish between the natural changes that occur with aging and the early-stage markers of lung disease. We don't just look at a printout; we look at the patient. If your results are outside the normal range, we use that data to create a personalized treatment plan, which might include medication, lifestyle changes, or advanced treatments like Zephyr endobronchial valves for emphysema.

Conclusion: Empowering Your Respiratory Health

Pulmonary function testing is the foundation of modern respiratory care. It moves us away from guesswork and toward precision medicine. Whether we are confirming a diagnosis of asthma, monitoring the progression of COPD, or evaluating your fitness for surgery, these tests provide the clarity needed to manage your health effectively.

If you are experiencing shortness of breath, a persistent cough, or have concerns about your lung health, don’t wait for symptoms to worsen. Get the data you and your doctor need to make informed decisions. Contact Muir Pulmonary Critical Care and Sleep Medicine in Walnut Creek today to schedule your comprehensive evaluation with our caring, expert team.