A lung function test, also known as a pulmonary function test (PFT), assesses how effectively your lungs operate. These non-invasive tests measure how much air your lungs can hold, how efficiently air moves in and out, and how well oxygen is absorbed into your bloodstream. PFTs help healthcare providers understand your lung health, diagnose various conditions, and monitor lung performance over time.
Reasons for Testing
Healthcare providers often recommend lung function tests for several medical reasons. If you experience symptoms like persistent shortness of breath, a chronic cough, wheezing, or chest tightness, a PFT can help identify the underlying cause. These tests are also valuable for diagnosing and monitoring known lung conditions such as asthma, chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis.
Beyond symptom evaluation, PFTs can be performed as part of a routine physical examination, especially for individuals with a history of smoking or exposure to environmental pollutants. They can also assess lung health before surgery, particularly in patients with existing lung or heart issues. Furthermore, these tests help determine how well current treatments for lung diseases are working and can guide adjustments to your care plan.
Before Your Appointment
Proper preparation before a lung function test helps ensure accurate results. You will typically be advised to avoid certain activities and substances in the hours leading up to your appointment. For example, refrain from smoking or vaping for at least one to four hours before the test, as tobacco can alter lung function and oxygen levels. Similarly, avoid heavy exercise for at least 30 minutes to one hour prior to the test.
It is also generally recommended to avoid large meals within two hours of the test, as a full stomach can restrict your diaphragm and prevent your lungs from fully expanding. Your doctor might instruct you to temporarily stop certain breathing medications, particularly bronchodilators, for a specified period before the test to get a baseline measurement of your lung function without medication effects. Wear loose, comfortable clothing that does not restrict your chest or abdomen, allowing for full and deep breaths during the procedure.
What Happens During the Test
The most common lung function test is spirometry, which measures how much air you can inhale and exhale, and how quickly you can exhale. When you arrive, a healthcare professional will guide you through the process, providing clear instructions and encouragement. You will typically be seated in a chair, and a soft clip will be placed on your nose to ensure all breathing occurs through your mouth.
Next, you will place your lips tightly around a mouthpiece connected to a spirometer. The technician will instruct you to take a deep breath, filling your lungs completely. Then, you will be asked to exhale as forcefully and quickly as possible, emptying your lungs fully. This forceful exhalation may be repeated several times, usually at least three, to ensure consistent and reliable results.
Sometimes, after an initial set of measurements, your doctor might give you an inhaled bronchodilator medication to open your airways. After waiting about 15 minutes, you will repeat the breathing maneuvers to see if the medication improves your lung function. This comparison helps determine if your airways respond to bronchodilators, which is useful in diagnosing conditions like asthma. The entire spirometry session typically takes no more than an hour.
Interpreting Your Results
After completing the lung function test, your healthcare provider will analyze the measurements to assess your lung health. Results are compared against predicted values, established averages for individuals of similar age, height, sex, and ethnicity, to determine if your lung function falls within a healthy range.
Two measurements frequently discussed are Forced Expiratory Volume in 1 second (FEV1) and Forced Vital Capacity (FVC). FEV1 measures the amount of air you can forcefully exhale in the first second after a deep breath, while FVC represents the total amount of air you can forcefully exhale after a full inhalation. The FEV1/FVC ratio helps differentiate between obstructive lung conditions, where airflow out of the lungs is hindered, and restrictive conditions, where the lungs cannot hold enough air.
A lower FEV1/FVC ratio can indicate an obstructive pattern, while a normal ratio with a reduced FVC might suggest a restrictive pattern. Your doctor will interpret these values in the context of your overall health history and symptoms. They will explain what your specific results mean and discuss any implications for your diagnosis, treatment plan, or further necessary tests.