Pulmonary function tests are a series of non-invasive tests that assess breathing and how well the lungs are working. Pulmonary function testing generally includes measurements of airflow, lung volume, and diffusion capacity, or the ability of the lungs to move oxygen from the air into the bloodstream and to move carbon dioxide from the bloodstream into the lungs.1
Measuring airflow
A spirometry test is used to measure airflow. The patient breathes into a mouthpiece that is connected to the spirometer. The spirometer measures the amount and rate of air that is breathed in and out over a period of time. Lung volume is measured in one of two ways. In body plethysmography, the patient sits in a transparent, airtight box and breathes in and out of a mouthpiece. The pressure changes inside the box are measured to determine lung volume. The second way lung volume is measured is by having the patient breathe nitrogen or helium gas through a tube for a short time. The concentration of gas in a container connected to the tube is measured to estimate lung volume. To measure diffusion capacity, the patient breathes a harmless gas for a short time, and the concentration of the gas in the air exhaled is measured and compared to the concentration of the gas inhaled.1
Using pulmonary function tests
Pulmonary function tests are used for several purposes, including:
- To evaluate and monitor diseases that affect how the heart and lungs function
- To diagnose certain lung diseases, including asthma, bronchitis, and emphysema
- To monitor the effects of environmental or occupational exposures
- To assess lung function before surgery
- To monitor the effects of medication on lung function
- To measure progress in disease treatment 1,2
Comparing to averages
Normal values for pulmonary function tests vary between people and are based on the patient’s age, height, ethnicity, and gender. Results from a patient’s pulmonary function tests will be compared to the average for people of the same age, height, gender, and ethnicity. Results are displayed as a percentage and are generally considered abnormal when they are less than 80% of the predicted value. Abnormal results indicate that some chest or lung disease is present.1,3
Measurements that can be included on pulmonary function test reports are:
- Diffusion capacity to carbon monoxide (DLCO)
- Expiratory reserve volume (ERV)
- Forced vital capacity (FVC)
- Forced expiratory volume in 1 second (FEV1)
- Forced expiratory flow 25% to 75% (FEF25-75)
- Functional residual capacity (FRC)
- Maximum voluntary ventilation (MVV)
- Residual volume (RV)
- Peak expiratory flow (PEF)
- Slow vital capacity (SVC)
- Total lung capacity (TLC) 1
Lung cancer patients
Pulmonary function tests are routinely performed on patients when they are diagnosed with lung cancer. The results from pulmonary function tests help inform the physicians which treatments are appropriate, such as radiation therapy and surgery. Surgery to remove lung cancer results in removing part or all of a lung, which can impact the lung’s ability to function. Before recommending surgery as an option, the patient’s lung function will be determined using pulmonary function tests.4,5
Possible risks
Pulmonary function tests are generally safe, however, there is a small risk of collapsed lung (pneumothorax) in people with a certain type of lung disease. Due to this risk, pulmonary function tests are not given to people who have had recent heart attacks, those with some other types of heart disease, or those who have recently experienced a collapsed lung.1
