What Does Expiratory Reserve Volume Measure?

Asthma Inhaler
Asthma Inhaler. Jonathan Ernst / Stringer / Getty Images

Expiratory reserve volume (abbreviated as ERV) refers to the extra volume of air that can be exhaled with maximum effort beyond the level reached at the end of a normal, passive exhalation.

In other words, if you've already exhaled normally and then attempt to empty your lungs completely by intentionally pushing all the air out of them that you can, that "extra" air is your expiratory reserve volume.

If you have breathing difficulties, your doctor may run several tests of your pulmonary function to get measurements that can help determine the severity of your condition. One of those tests is expiratory reserve volume.

The opposite of expiratory reserve volume is inspiratory reserve volume, which — as you might imagine — measures the amount of extra air you can intentionally draw into your lungs after you've breathed in normally. This also is a test performed to see how well your lungs are functioning.

Conditions Where Expiratory Reserve Volume Is Important

There are several conditions where your expiratory reserve volume may provide clues as to the health of your lungs. These conditions include:

Your doctor may run this test as part of the process of diagnosis to determine why exactly you're having symptoms such as difficulty breathing, chronic cough, wheezing, and signs of low oxygen in your blood.

She may also run the test as part of the ongoing monitoring of your condition, to determine if you've stabilized or if your lung function has declined further.

Finally, sometimes these tests are run to screen for lung problems in smokers or in people with jobs that place them at risk for lung disease — for example, they may be exposed to toxic chemicals at work.

What Can Expiratory Reserve Volume Tell You?

Your doctor won't diagnose you based only on the results of your expiratory reserve volume lung test. The test itself most likely will take place as part of your overall lung function tests, which also are likely to include multiple other measures of your lungs' volume and capacity.

Spirometry is one of the most commonly run tests of lung function, but there are many others. Learn more:

Your expiratory reserve volume test can, however, provide your doctor with clues about your condition. Those clues, combined with your medical history and the results of your exam, should lead your doctor to the correct diagnosis.

Sources:

Al-Ashkar F et al. Interpreting pulmonary function tests: Recognize the pattern,and the diagnosis will follow. Cleveland Clinic Journal of Medicine. October 2003. Volume 70, Number 10.

U.S. National Library of Medicine. Pulmonary Function Tests fact sheet. Accessed Feb. 6, 2016.

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