Spirometry Test

Overview of Spirometry

Spirometry is a powerful tool that can be used to detect, follow, and manage patients with lung disorders.

Spirometry is used to diagnose asthma, chronic obstructive pulmonary disease (COPD) and other conditions that affect breathing. Spirometry may also be used periodically to monitor your lung condition and check whether a treatment for a chronic lung condition is helping you breathe better.

 A simplified and stepwise method is key to interpreting spirometry. The first step is determining the validity of the test. Next, the determination of an obstructive or restrictive ventilatory patten is made. If a ventilatory pattern is identified, its severity is graded. In some patients, additional tests such as static lung volumes, diffusing capacity of the lung for carbon monoxide, and bronchodilator challenge testing are needed. These tests can further define lung processes but require more sophisticated equipment and expertise available only in a pulmonary function laboratory.

Why it’s done

Your doctor may suggest a spirometry test if he or she suspects your signs or symptoms may be caused by a chronic lung condition such as:

  • Asthma
  • COPD
  • Chronic bronchitis
  • Emphysema
  • Pulmonary fibrosis

If you’ve already been diagnosed with a chronic lung disorder, spirometry may be used periodically to check how well your medications are working and whether your breathing problems are under control. Spirometry may be ordered before a planned surgery to check if your lung function is adequate for the rigors of an operation. Additionally, spirometry may be used to screen for occupational-related lung disorders.

Risks

Spirometry is generally a safe test. You may feel short of breath or dizzy for a moment after you perform the test.

Because the test requires some exertion, it isn’t performed if you’ve had a recent heart attack or some other heart condition. Rarely, the test triggers severe breathing problems.

How you prepare

Follow your doctor’s instructions about whether you should avoid use of inhaled breathing medications or other medications before the test. Other preparations include the following:

  • Wear loose clothing that won’t interfere with your ability to take a deep breath.
  • Avoid eating a large meal before your test, so it will be easier to breathe.

What you can expect

 

A spirometry test requires you to breathe into a tube attached to a machine called a spirometer. Before you do the test, a nurse, a technician or your doctor will give you specific instructions. Listen carefully and ask questions if something is not clear. Doing the test correctly is necessary for accurate and meaningful results.

In general, you can expect the following during a spirometry test:

  • You’ll likely be seated during the test.
  • A clip will be placed on your nose to keep your nostrils closed.
  • You will take a deep breath and breathe out as hard as you can for several seconds into the tube. It’s important that your lips create a seal around the tube, so that no air leaks out.
  • You’ll need to do the test at least three times to make sure your results are relatively consistent. If there is too much variation among the three outcomes, you may need to repeat the test again. The highest value among three close test results is used as the final result.
  • The entire process usually takes less than 15 minutes.

Your doctor may give you an inhaled medication to open your lungs (bronchodilator) after the initial round of tests. You’ll need to wait 15 minutes and then do another set of measurements. Your doctor then can compare the results of the two measurements to see whether the bronchodilator improved your airflow.

Spirometry measures the rate at which the lung changes volume during forced breathing maneuvers. Spirometry begins with a full inhalation, followed by a forced expiration that rapidly empties the lungs. Expiration is continued for as long as possible or until a plateau in exhaled volume is reached. These efforts are recorded and graphed.

Lung function is physiologically divided into four volumes: expiratory reserve volume, inspiratory reserve volume, residual volume, and tidal volume. Together, the four lung volumes equal the total lung capacity (TLC). Lung volumes and their combinations measure various lung capacities such as functional residual capacity (FRC), inspiratory capacity, and VC.

Results

Key spirometry measurements include the following:

  • Forced vital capacity (FVC). This is the largest amount of air that you can forcefully exhale after breathing in as deeply as you can. A lower than normal FVC reading indicates restricted breathing.
  • Forced expiratory volume (FEV). This is how much air you can force from your lungs in one second. This reading helps your doctor assess the severity of your breathing problems. Lower FEV-1 readings indicate more significant obstruction.

Glossary

Spirometric values

FVC—Forced vital capacity; the total volume of air that can be exhaled during a maximal forced expiration effort.

FEV1—Forced expiratory volume in one second; the volume of air exhaled in the first second under force after a maximal inhalation.

FEV1/ FVC ratio—The percentage of the FVC expired in one second.

FEV6 —Forced expiratory volume in six seconds.

FEF25–75%—Forced expiratory flow over the middle one half of the FVC; the average flow from the point at which 25 percent of the FVC has been exhaled to the point at which 75 percent of the FVC has been exhaled.

MVV—Maximal voluntary ventilation.

Lung volumes

ERV—Expiratory reserve volume; the maximal volume of air exhaled from end-expiration.

IRV—Inspiratory reserve volume; the maximal volume of air inhaled from end-inspiration.

RV—Residual volume; the volume of air remaining in the lungs after a maximal exhalation.

VT —Tidal volume; the volume of air inhaled or exhaled during each respiratory cycle.

Lung capacities

FRC—Functional residual capacity; the volume of air in the lungs at resting end-expiration.

IC—Inspiratory capacity; the maximal volume of air that can be inhaled from the resting expiratory level.

TLC—Total lung capacity; the volume of air in the lungs at maximal inflation.

VC—Vital capacity; the largest volume measured on complete exhalation after full inspiration.

The most important spirometric maneuver is the FVC. To measure FVC, the patient inhales maximally, then exhales as rapidly and as completely as possible. Normal lungs generally can empty more than 80 percent of their volume in six seconds or less. The forced expiratory volume in one second (FEV1) is the volume of air exhaled in the first second of the FVC maneuver. The FEV1/FVC ratio is expressed as a percentage (e.g., FEV1 of 0.5 L divided by FVC of 2.0 L gives an FEV1/FVC ratio of 25 percent). The absolute ratio is the value used in interpretation, not the percent predicted.
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