Pulmonary Function Tests (PFTs) are a group of non-invasive tests that assess how well the lungs function. These tests measure various aspects of lung performance, including how much air the lungs can hold, how efficiently air moves in and out, and how effectively oxygen is transferred from the lungs into the bloodstream. PFTs provide objective information about respiratory health, helping healthcare providers understand the overall capacity and efficiency of the respiratory system.
Why a PFT is Performed
Healthcare providers utilize Pulmonary Function Tests to diagnose and manage a range of lung conditions. These tests can help identify lung diseases such as asthma, chronic obstructive pulmonary disease (COPD), emphysema, or pulmonary fibrosis. PFTs are also instrumental in monitoring the progression of known lung diseases over time. Beyond diagnosis and monitoring, PFTs evaluate the effectiveness of ongoing treatments for respiratory conditions. Additionally, PFTs are often performed to assess lung function before surgical procedures and to determine the underlying cause of persistent symptoms like shortness of breath or a chronic cough.
Common Tests Performed
A Pulmonary Function Test typically involves several distinct measurements. The most common component is spirometry, which measures the amount of air a person can inhale and exhale, and how quickly they can do so. During spirometry, a patient breathes into a mouthpiece connected to a device called a spirometer. This test quantifies forced vital capacity (FVC), representing the total amount of air exhaled forcefully after a deep breath, and forced expiratory volume in one second (FEV1), which is the volume of air expelled in the first second of that forceful exhalation. Spirometry is widely used to identify obstructive lung diseases, where airflow out of the lungs is impaired.
Another important aspect of PFTs involves lung volume measurements, which determine the total amount of air the lungs can hold and how much air remains after exhalation. These measurements include residual volume (RV), the air left in the lungs after a maximal exhalation, and total lung capacity (TLC), the total volume of air in the lungs after a maximal inhalation. Functional residual capacity (FRC) is also measured, representing the volume of air remaining in the lungs after a normal, relaxed exhalation. These volumes are often determined using methods like body plethysmography or gas dilution techniques. Lung volume measurements are particularly helpful in diagnosing restrictive lung diseases, where the lungs cannot fully expand.
The diffusing capacity of the lung for carbon monoxide (DLCO) is another key test, assessing how efficiently gases transfer from the air sacs (alveoli) in the lungs into the bloodstream. This test is typically performed using a single-breath technique, where the patient inhales a small, harmless concentration of carbon monoxide mixed with other gases, holds their breath for about 10 seconds, and then exhales. The amount of carbon monoxide absorbed by the blood is measured, providing an indication of the function of the alveolar-capillary membrane. A reduced DLCO can suggest conditions that affect the gas exchange surface of the lungs, such as emphysema or pulmonary fibrosis.
Preparing for a PFT
Patients are usually advised to avoid smoking for at least four hours before the test, as tobacco use can temporarily affect lung function. Heavy meals should also be avoided for a few hours prior to the test, and caffeine intake may need to be limited, as these can sometimes interfere with optimal breathing mechanics. Regarding medications, patients might be instructed to temporarily stop taking certain breathing medicines, particularly bronchodilators, for a specified period before the test. Patients should also refrain from strenuous exercise before the test and wear comfortable, loose-fitting clothing that does not restrict breathing. Informing the testing facility about any recent illnesses, such as a cold or flu, is also important, as this could temporarily impact lung function and may necessitate rescheduling the test.
Understanding Your PFT Results
Once a Pulmonary Function Test is complete, the results are interpreted by a healthcare professional. The interpretation considers several personal factors, including the patient’s age, sex, height, and sometimes ethnicity, as these variables naturally influence lung capacity and function. The measured values from the PFT are then compared to predicted normal values for individuals with similar characteristics.
General patterns in the results can indicate different types of lung issues. For instance, obstructive lung diseases, like asthma or COPD, involve a reduced ability to exhale air quickly. Conversely, restrictive lung diseases, where the lungs cannot expand fully, typically show reduced lung volumes. Sometimes, a mixed pattern indicating both obstructive and restrictive components may be identified. The healthcare provider will discuss these findings, explaining what the results mean for the patient’s specific health condition and outlining any necessary next steps for diagnosis or treatment.