Pulmonary Function Tests Help Healthcare Professionals Diagnose Lung Conditions and Prescribe the Best Treatment.
Healthcare providers use pulmonary function tests (also called PFTs or lung function tests) to determine how well your lungs are working.
PFTs are accurate, painless, and noninvasive (meaning there’s no incision or cutting of the skin).
Your doctor may order a PFT if you have symptoms such as shortness of breath, coughing, or chest tightness. Sometimes, a PFT is just part of a routine physical.
Healthcare providers also use PFTs to diagnose such respiratory conditions as COPD (chronic obstructive pulmonary disease). An accurate diagnosis is the first step in prescribing the most effective treatment plan.
PFTs Can Help Diagnose Both Forms of Lung Disease
Both obstructive lung disease and restrictive lung disease cause symptoms such as shortness of breath. But the two diseases differ in when they cause you to have breathing problems.
Obstructive lung disease, such as COPD and asthma, occurs when your airway is blocked, making it harder to exhale.
Restrictive lung disease, such as pneumonia and tuberculosis, occurs when your lungs can’t fully expand, making it harder to inhale.
What PFTs Measure
PFTs can measure many parameters of lung health, including:
Total lung capacity: The total volume of air your lungs can hold after maximum inhalation.
Tidal volume (VT): The amount of air that moves in and out of your lungs each time you breathe while you're at rest.
Minute volume (MV): The volume of gas inhaled or exhaled from your lungs in one minute.
Vital capacity (VC): The maximum amount of air you can exhale after inhaling as much air as you can.
Functional residual capacity (FRC): The total volume of air remaining in your lungs after you exhale normally.
Residual volume: The volume of air remaining in your lungs after maximum exhalation.
Forced vital capacity (FVC): The total volume of air that can be exhaled forcefully from your lungs after taking the deepest breath possible.
Forced expiratory volume (FEV): The total amount of air exhaled during the first, second, and third seconds of an FVC test.
Forced expiratory flow (FEF): The rate of airflow during the middle of an FVC test.
Peak expiratory flow rate (PEFR): The speed at which you can exhale air from your lungs.
Four Widely Used PTFs
1. Spirometry
The most basic and common of all pulmonary function tests, spirometry measures how much air you can inhale and how quickly you can blow it out.
Your doctor will place a soft clip on your nose, forcing you to breathe through your mouth. You place your lips around a mouthpiece that’s connected to a small electronic device called a spirometer.
You then inhale and exhale deeply through the mouthpiece. The spirometer measures the results to help with your doctor’s diagnosis.
2. Lung volume test (also called body plethysmography)
This is another common test—and more precise than spirometry. This test measures the total volume of air in your lungs, including the amount that remains after you completely exhale.
Your doctor attaches nose clips. You then sit in a see-through plastic box. You’ll be instructed to breathe in and out through your mouth through a mouthpiece. The test takes about 5 minutes.
3. Gas diffusion study
A gas diffusion study assesses how well your lungs deliver oxygen and other gases to your blood.
You wear a nose clip and breathe through a mouthpiece connected to a spirometer. You inhale a very small, safe amount of carbon monoxide gas and hold your breath for about 10 seconds.
As you exhale, the spirometer measures the amount of carbon dioxide, which reveals how much gas your lungs absorb and transfer into your blood.
4. Cardiopulmonary exercise test (CPET)
CPET measures how well your lungs, heart, and muscles function during exercise. It’s often given to people with lung disorders or heart problems, which may occur when exercising.
Your doctor uses monitors that measure breathing, blood pressure, heart rate, and blood oxygen levels as you exercise.
You also breathe through a mouthpiece or face mask connected to a monitor that measures the amount of oxygen you inhale and the amount of carbon dioxide you exhale.
You'll ride a stationary bicycle or walk on a treadmill for 10-20 minutes. Your doctor will monitor you throughout the test.
How to Prepare for a PFT
PFTs are performed by a pulmonary function technician and take 15-45 minutes to complete. Here are tips to prepare:
- Take your daily medications before the test unless your doctor tells you not to
- If you’ve been prescribed a short-acting inhaler, try not to use it 6-8 hours before the test, if possible (but be sure to discuss with your doctor first)
- Wear loose-fitting clothes and comfortable shoes
- Avoid any heavy exercise at least 30 minutes before the test
- Don’t smoke, drink alcohol, or consume foods with caffeine
- Don’t eat a heavy meal at least 2 hours before your test
- Empty your bladder before the test
If at any time during the test you feel tired, let the technician know.
PFTs: the Time-Tested Tests
If you’re experiencing shortness of breath, wheezing, chest tightness, or chronic coughing, speak with your doctor. A pulmonary function test can help easily and accurately diagnose your condition—which can lead to effective treatment and better breathing.
References
1. (Updated 2023, March 7). What Are Lung Function Tests and Why Are They Done? American Lung Association. https://www.lung.org/lung-health-diseases/lung-procedures-and-tests/lung-function-tests.
2. (Updated 2022, October 12). Pulmonary Function Testing. Cleveland Clinic. https://my.clevelandclinic.org/health/diagnostics/17966-pulmonary-function-testing.
3. Pulmonary Function Tests. Johns Hopkins Medicine. https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/pulmonary-function-tests.
4. Khatri, M. (2022, August 14). Pulmonary Function Test.
WebMD. https://www.webmd.com/lung/types-of-lung-function-tests.
5. Lung Function Tests. MedlinePlus. https://medlineplus.gov/lab-tests/lung-function-tests/.
6. Leader, D. (Updated 2023, August 23). Obstructive vs. Restrictive Lung Diseases: Causes and Treatment. Verywell Health. https://www.verywellhealth.com/obstructive-and-restrictive-lung-diseases-914741
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