Pulmonary Function Tests (PFTs) are a set of non-invasive breathing assessments that provide detailed information about how well your lungs are working. These tests are performed by specialized healthcare professionals to objectively measure the mechanics of your breathing.
Defining Pulmonary Function Tests
Pulmonary function tests are assessments designed to evaluate the mechanical performance of the respiratory system, including the lungs, airways, and the chest wall. These evaluations quantify the physical aspects of breathing. The tests focus on two core physiological concepts: how much air the lungs can hold (volume and capacity) and how quickly air can be moved in and out (flow rate).
The results provide objective data on the elasticity of the lung tissue and the resistance within the air passages. PFTs help to create a functional map of the respiratory system by measuring these physical properties. This assessment measures lung performance against predicted values based on a person’s age, sex, height, and ethnicity. Analyzing these numbers allows clinicians to identify patterns of breathing impairment not apparent from a physical exam alone.
Clinical Reasons for Testing
A physician may recommend PFTs to investigate symptoms like a persistent cough, wheezing, or shortness of breath. The primary role of the testing is to aid in the diagnosis of various respiratory conditions by characterizing the nature of any breathing difficulty. PFTs are particularly effective at distinguishing between two main categories of lung problems: obstructive and restrictive diseases.
Obstructive diseases are characterized by difficulty exhaling air due to narrowed airways, while restrictive diseases involve a reduced total lung volume, making it hard to fully inhale. Beyond initial diagnosis, PFTs serve an important role in monitoring the progression of known lung diseases, such as those caused by environmental or occupational exposure. The results establish a baseline to track disease severity over time and evaluate whether the patient is declining, stable, or improving.
The tests are also used to assess the effectiveness of treatment plans, such as newly prescribed bronchodilator medications. A repeat PFT can show if lung function measurably improves after treatment is started, helping the doctor to adjust dosage or switch therapies. PFTs are often a routine part of a pre-operative assessment for patients scheduled for certain surgeries, especially those involving the chest or for individuals with known heart or lung conditions. This evaluation helps predict a patient’s ability to tolerate the procedure and recover afterward.
The Testing Procedure and Key Measurements
The most common type of pulmonary function test is spirometry, which is typically the starting point for a full PFT workup. During this procedure, the patient sits and uses a disposable mouthpiece connected to a spirometer machine. A soft clip is placed on the nose to ensure all breathing is performed through the mouth, maximizing the accuracy of the measurements.
The patient is coached by a technician to perform specific breathing maneuvers, which require maximal effort and cooperation for reliable results. The most important maneuver involves taking the deepest breath possible and then forcibly exhaling as quickly and completely as possible. This forceful, sustained exhalation is the basis for the three most informative measurements used in clinical practice.
The first measurement is the Forced Vital Capacity (FVC), which represents the total volume of air the patient can forcefully exhale after a maximal inspiration. A reduced FVC suggests the patient is unable to fully fill their lungs, a common finding in restrictive lung disorders. The second measurement is the Forced Expiratory Volume in 1 second (FEV1), which is the volume of air expelled during the first second of that forceful exhalation. This value is a direct indicator of the airflow rate through the larger airways.
The FEV1/FVC ratio is the third and most significant measurement, comparing the flow rate to the total volume. This ratio is expressed as a percentage and is the primary tool for differentiating between the two main types of respiratory impairment. In a normal adult, the FEV1 is typically 70% or more of the FVC, meaning most of the air is expelled almost immediately.
An obstructive pattern is indicated when the FEV1 is disproportionately low compared to the FVC, resulting in a reduced FEV1/FVC ratio. This suggests that while the total lung capacity may be near normal, air takes longer to exit due to airway narrowing. Conversely, a restrictive pattern is suggested by a low FVC, but a normal or high FEV1/FVC ratio. In this case, the airways are open, but the total volume of air the lungs can hold is reduced, causing both the FEV1 and FVC to decrease proportionally.
To ensure accurate test results, patients are advised on specific preparation requirements before their appointment. They may be asked to avoid large meals or heavy exercise in the hours leading up to the test, and sometimes they must temporarily stop using specific inhaled medications, as directed by their physician. A high-quality PFT depends on the patient’s maximal effort and adherence to these instructions.