Lung function tests, often referred to as pulmonary function tests (PFTs), are a group of non-invasive diagnostic procedures. These tests evaluate how well an individual’s lungs are working. They help assess lung capacity, airflow, and the efficiency of gas exchange.
These assessments provide objective measurements that assist healthcare professionals in diagnosing various respiratory conditions. They also monitor the progression of known lung diseases and evaluate treatment effectiveness. The information gathered helps understand the mechanical function of the lungs and airways.
Key Lung Function Tests
Spirometry is the most common lung function test, measuring the amount of air a person can breathe out and how quickly they can do it. This test provides specific values like Forced Vital Capacity (FVC), which is the total amount of air exhaled after a deep breath, and Forced Expiratory Volume in one second (FEV1), the volume of air exhaled in the first second of a forced breath. These measurements help identify potential airflow limitations.
Lung volume measurements, such as those performed using body plethysmography, assess the total amount of air the lungs can hold. This test provides a more complete picture of lung capacity beyond what can be measured by spirometry alone. It helps distinguish between different types of lung disorders by measuring residual volume and total lung capacity.
Diffusion capacity, often called DLCO (Diffusing Capacity of the Lung for Carbon Monoxide), measures how effectively oxygen moves from the lungs into the bloodstream. This test involves breathing a small, safe amount of carbon monoxide, and it helps evaluate the integrity of the lung’s air sacs and capillaries. A reduced diffusion capacity can indicate damage to the lung’s gas exchange surface.
Preparing for Your Test
Several steps ensure accurate results when preparing for a lung function test. Avoid bronchodilator medications for four to eight hours before the test, unless instructed otherwise. This allows lung assessment without temporary widening effects.
Patients should refrain from smoking for at least one hour and avoid consuming alcohol for four hours prior to the test. Strenuous exercise should be avoided for at least 30 minutes before the appointment, as it can temporarily alter breathing patterns and lung capacity. Eating a heavy meal immediately before the test is also not advised, as it can cause discomfort during the forced breathing maneuvers.
Wearing loose, comfortable clothing is recommended to avoid any restriction around the chest and abdomen, which could impede full lung expansion. Always follow specific instructions from your doctor or testing facility, as guidelines may vary.
What Happens During the Test
During a lung function test, especially spirometry, the patient sits comfortably upright. A trained technician explains each step and guides the patient through breathing maneuvers, offering encouragement for accurate results.
A soft nose clip will be placed on the patient’s nose to ensure that all air passes through the mouth. The patient will then be asked to seal their lips tightly around a disposable mouthpiece connected to the spirometer machine. The technician will instruct the patient to breathe normally for a few breaths to establish a baseline.
The patient inhales as deeply as possible, filling their lungs completely. Immediately after, they exhale as forcefully and quickly as possible, emptying their lungs. This forced exhalation must continue until no more air can be expelled, typically for at least six seconds in adults.
The technician emphasizes a “blast” or “push” at the start of exhalation and sustained effort. After forced exhalation, the patient may quickly inhale to measure inspiratory capacity. The entire sequence is repeated three to eight times for consistent, reliable measurements.
The technician continuously monitors the real-time graphs displayed on the spirometer, ensuring the patient performs the maneuvers correctly and consistently. If the effort is not satisfactory, the technician will provide feedback and ask the patient to try again. This iterative process helps obtain high-quality, reproducible data necessary for accurate interpretation.
Interpreting Your Results
Interpreting lung function test results involves analyzing several key metrics, with FEV1, FVC, and the FEV1/FVC ratio being particularly significant. FEV1 represents the volume of air forcefully exhaled in the first second, while FVC is the total volume of air forcefully exhaled after a maximal inspiration. The ratio of FEV1 to FVC indicates the proportion of total lung capacity that can be exhaled quickly.
These measured values are compared to predicted normal values, which are established based on a person’s age, height, sex, and ethnicity. A result is considered normal if it is 80% or more of the predicted value. Deviations from these predicted values can suggest the presence of a lung condition.
Patterns in these results help healthcare professionals differentiate between different types of lung diseases. For example, a reduced FEV1/FVC ratio indicates an obstructive lung condition like asthma or COPD, where airflow is hindered. Conversely, reduced FEV1 and FVC with a preserved or increased FEV1/FVC ratio suggests a restrictive lung condition, such as pulmonary fibrosis, where lung expansion is limited.
A healthcare professional will interpret these results in the broader context of the patient’s medical history, physical examination, and symptoms. The numbers from the lung function test provide objective data that, when combined with other clinical information, aid in accurate diagnosis and the formulation of an appropriate management plan.