Flow volume loop tests measure how much airflow a person can produce when breathing relative to their lung volume. This test can help doctors diagnose chronic obstructive pulmonary disease (COPD).

The term “COPD” refers to conditions that cause blockages in airflow and other breathing problems. COPD can lead to wheezing, coughing, and shortness of breath.

Around 15.7 million people have COPD in the United States. Doctors may use a flow volume loop test when diagnosing COPD and other respiratory conditions.

This article explains flow volume loop for COPD, including what to expect from the procedure, how to interpret the results, and the next steps.

A person using a spirometer during a COPD flow volume test.-2Share on Pinterest
Lourdes Balduque/Getty Images

A flow volume loop test is a procedure that assesses someone’s lung airflow in relation to their lung volume. The flow volume loop test measures lung airflow in liters of air per second and lung volume in liters.

Flow volume loop tests are important when doctors want to determine whether someone has the expected airflow for the amount of lung volume they have. This procedure can help doctors diagnose various respiratory conditions, including COPD.

Learn about other lung function tests.

Healthcare professionals administer a flow volume loop test using spirometry, a procedure that can allow doctors to determine someone’s airflow and lung volume.

According to the American Lung Association, spirometry may require some preparation. Doctors might advise people to stop using certain inhalers or medications, wear loose-fitting clothes, and avoid large meals just before the test.

During a spirometry test, a person must sit upright with a clip on their nostrils. They must breathe in and out through a mouthpiece, keeping their lips sealed firmly so the air flows into the spirometry apparatus.

A pulmonary function specialist will administer the test. They may repeat the procedure several times to achieve the most reliable results. The test should not cause pain or discomfort.

Flow volume loop tests can yield several different results, which a doctor can interpret in the following ways:

  • Normal: People with normal results on a flow volume loop test have no indication of a respiratory problem.
  • Obstructive disorder: This result shows that general airflow is lower than expected, especially when it comes to exhaling. This can indicate conditions such as emphysema, asthma, and COPD.
  • Restrictive disorder: This result shows that someone has a lower-than-expected lung volume. However, there is also an above-average amount of airflow relative to the size of the lungs. This can indicate interstitial lung disease and kyphoscoliosis.
  • Fixed obstruction of the upper airway: This result shows an equal limitation in airflow during inhalation and exhalation. This indicates conditions such as tracheal stenosis and goiter.
  • Variable extrathoracic obstruction: This result indicates problems with vocal cords, such as unilateral vocal cord paralysis or vocal cord dysfunction. Such conditions can lead to the vocal cord blocking airflow into the lungs.
  • Variable intrathoracic obstruction: This result can indicate problems with the trachea, such as tracheomalacia, where the trachea collapses when someone breathes out. This can cause a limitation in airflow during exhalation.

If a doctor suspects that someone may have COPD based on the results of a flow volume test, they may suggest further testing to determine its severity. According to a 2023 review, these tests might include:

  • a questionnaire to determine how breathless the affected person feels
  • a 6-minute walk test that measures lung function in relation to physical activity
  • blood tests for comorbidities of COPD, including infections and anemia
  • imaging tests, including chest X-rays and CT scans, which can help determine possible causes of COPD

Treatment for COPD can involve lifestyle modifications, such as smoking cessation, and lung rehabilitation, which involves a complex and personalized combination of exercise, education, and behavioral modification.

People with COPD may also benefit from medications, such as bronchodilators to relax muscles in the airways and corticosteroids to reduce inflammation.

COPD is a serious condition that causes breathing problems. Doctors may use a flow volume loop test when diagnosing COPD.

This test measures how much airflow someone can produce when breathing, given their lung volume. A flow volume loop test requires people to breathe through a mouthpiece into a machine that measures airflow.

People with COPD will have reduced overall airflow, especially when breathing out. Doctors may recommend lifestyle changes and medication to treat affected people.