Pulmonary function tests (PFTs) are non-invasive breathing tests that evaluate how well your lungs function. They provide a comprehensive assessment of respiratory health, measuring how air moves in and out of your lungs and how effectively oxygen is absorbed into your bloodstream. PFTs serve as a diagnostic tool to assess overall lung capacity and identify the severity of pulmonary impairment.
What PFT Measures
Pulmonary function tests assess several physiological aspects of lung activity. They measure lung volumes, quantifying the amount of air your lungs can hold and move. Key volumes include total lung capacity (TLC), the maximum air in the lungs after a full inhalation, and residual volume (RV), the air remaining after maximal exhalation. Functional residual capacity (FRC) indicates the air left in the lungs after a normal breath out.
PFTs also evaluate airflow rates, measuring how quickly air moves into and out of the lungs. Forced vital capacity (FVC) is the total amount of air you can forcefully exhale after a deep breath. Forced expiratory volume in one second (FEV1) indicates the air exhaled during the first second of this forceful breath. The ratio of FEV1 to FVC (FEV1/FVC) is particularly informative for identifying airflow obstruction.
Gas exchange is another process assessed by PFTs, measuring how efficiently oxygen moves from the lungs into the bloodstream. This is evaluated through the diffusing capacity of the lung for carbon monoxide (DLCO). The DLCO test uses a small, safe amount of carbon monoxide to gauge the transfer of gases across the alveolar-capillary membranes in the lungs.
How PFTs Are Performed
Pulmonary function tests involve several distinct procedures. Spirometry is the most common PFT, where you breathe into a mouthpiece connected to a spirometer. You take a deep breath in, then exhale as forcefully and rapidly as possible into the mouthpiece, often for several seconds. Nose clips are worn to ensure all air passes through the mouth, and the test is usually repeated multiple times for consistent and accurate results.
Measuring lung volumes beyond spirometry requires specialized techniques. Body plethysmography involves sitting inside an airtight chamber where pressure changes are measured as you breathe. This method helps determine lung volumes like functional residual capacity, total lung capacity, and residual volume. Alternative methods include helium dilution and nitrogen washout, which involve breathing specific gas mixtures to calculate lung volumes.
The diffusion capacity test (DLCO) measures gas transfer efficiency. For this test, you inhale a gas mixture containing a small amount of carbon monoxide, hold your breath for about 10 seconds, and then exhale. The equipment measures how much of the carbon monoxide was absorbed, indicating how well gases transfer from your lungs to your blood.
When PFTs Are Used
Pulmonary function tests are ordered for diagnostic and monitoring purposes in respiratory care. They diagnose lung diseases, including obstructive conditions like asthma and chronic obstructive pulmonary disease (COPD), where airflow is restricted. PFTs also identify restrictive lung diseases, such as pulmonary fibrosis, where the lungs cannot expand fully.
PFTs monitor the progression of known lung conditions over time. Regular tests track changes in lung function, helping healthcare providers assess disease severity and adjust treatment plans accordingly. This includes evaluating the effectiveness of medications or other interventions for conditions like asthma or COPD.
PFTs play a role in pre-surgical evaluations, especially before thoracic or upper abdominal surgeries, to assess a patient’s lung health and potential risks. They evaluate respiratory symptoms such as shortness of breath, chronic cough, or wheezing, helping to pinpoint the underlying cause. PFTs are also used in occupational health to monitor lung function in individuals exposed to airborne toxins or irritants in the workplace.
Understanding Your PFT Results
Interpreting pulmonary function test results involves comparing your measured values to predicted normal values. These predicted values are based on factors such as your age, sex, height, and ethnicity, providing a personalized benchmark for healthy lung function. A healthcare professional reviews the quality of the test, ensuring the measurements are reliable, before proceeding with interpretation.
Results are typically presented as a percentage of the predicted value. For instance, a forced expiratory volume in one second (FEV1) or forced vital capacity (FVC) above 80% of the predicted value is generally considered within the normal range. A diffusion capacity (DLCO) above 75% of the predicted value is often deemed normal.
Abnormal results can indicate specific patterns of lung disease. An obstructive pattern, commonly seen in asthma or COPD, is characterized by a disproportionately low FEV1/FVC ratio, meaning air has trouble flowing out quickly. A restrictive pattern, associated with conditions like pulmonary fibrosis, shows reduced lung volumes, such as total lung capacity (TLC), with a normal or even elevated FEV1/FVC ratio. PFT results are always interpreted by a healthcare professional in the context of your overall health, symptoms, and medical history.