Children's Hospital Colorado

Pulmonary Function Laboratory

Our experts treat respiratory and sleep disorders from the common to the complex, helping children and families breathe easier.

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patient breathes into Pulmonary Function Laboratory device.

The Pulmonary Function Lab at Children's Hospital Colorado offers a variety of different pulmonary function tests (PFTs). Our Pulmonary Lab specializes in testing children and teens.

The PFTs are non-invasive and painless. Tests are designed to measure the amount of air in the lungs, and how the lungs function by moving air in and out. Most kids find that they are fun to do and look forward to clinic visits where they get to "blow the house down."

Our lab is registered by the American Thoracic Society, and all tests are performed to the standards set by the Society. All tests are performed by licensed respiratory therapists who are registered or certified in pulmonary function testing. We also have satellite clinics that offer simple spirometry.

Why use PFTs?

PFTs can tell us about what type of lung disease a child has, how the disease is changing over time and how their disease is responding to treatments.

PFTs are commonly used to help diagnose and treat patients with asthma, cystic fibrosis and other lung diseases. They can be used to monitor the response to different therapies prescribed and can help measure the effects of cancer drugs on the lungs. They can also be used to determine the effect on the lungs from curvatures of the spine or deformities of the breastbone.

What to expect

The therapist will put your child at ease by making the tests fun, answering questions and coaching throughout each maneuver. Soft nose clips and a mouthpiece filter are used for each maneuver. The amount of maneuvers depends on the patient's age and technique. We strive to make the tests fun so the child looks forward to doing PFTs. 

Common PFTs

Common tests performed in the Pulmonary Function Lab include:


The individual takes as deep a breath as possible and blows out their air as fast as possible until their lungs are completely empty. Most of our equipment has incentive screens to help coach by using visuals such as blowing the three pigs houses down.

In general, cooperative children starting between ages 3 and 6 can perform spirometry. The spirometer measures the volume of air breathed out and the time it take to do this. It reports these numbers as absolute numbers and percent predicted compared to normal healthy children of the same height, weight and gender.

This test measures the total amount of air the child breaths out (forced vital capacity or FVC) and the amount the child breaths out in the first second (forced expiratory volume in 1 second or FEV1). By looking at these 2 numbers, and the ratio of FEV1/FVC, we can predict if the child has abnormal lung function and the type of lung abnormally present.

If the FEV1 and FVC are low and the ratio of FEV1/FVC is normal, this is called restrictive lung disease. This is seen when the lungs are small or stiff or are confined by the rib cage. If the FEV1 and FEV1/FVC are low, this is called obstructive lung disease. This is seen most commonly in asthma or diseases that affect the airways and how fast a child can breath out. There are some diseases which have a combination of mixed obstructive and restrictive lung disease.

Lung Volumes (Body Plethysmography or Nitrogen Washout)

These tests measure many things, including how much total air is in the lungs (total lung capacity or TLC), how much air is in the lungs when you normally breath out (functional residual capacity or FRC) and how much air is left after you breath out all the air you can (residual volume or RV).

In restrictive lung disease, generally all the lung volumes are low. In some lung diseases, there is air trapping in which the RV and FRC are high representing extra air in the lungs.

  • Body plethysmography requires the child to sit in a clear Plexiglas booth and breathe through the mouthpiece filter. Pressure and volume changes are measured to determine lung volumes.
  • Nitrogen washout requires the patient to breathe 100% oxygen until the nitrogen level in the lungs reaches a certain percentage. A calculation is made to determine lung volume.

Diffusion Capacity

This test requires the individual to inhale a diffusion gas and hold their breath for 10 seconds. It measures how efficient gas exchange is in the lungs.

Exercise Induced Bronchoconstriction (EIB) Test

This test is performed by doing a series of spirometry maneuvers before and following vigorous exercise on a treadmill. It measures airway reactivity to exercise.  

Methacholine Challenge

This type of test uses an aerosolized challenge agent called methacholine to determine airway reactivity. It involves the patient breathing the agent and doing a series of spirometry tests.

Infant Pulmonary Function Tests

Infant PFTs are a special type of pulmonary function test that is only done in specialized centers like Children's Colorado.

In infants, lung function testing requires sedation, usually medication by mouth, so the child sleeps and is passive during the test. This allows the infant PFT equipment to perform testing since the child is not old enough to cooperate with PFTs. Infant PFTs can be performed very early in life until about 2 to 4 year of age depending on the equipment and size of the child.

Once children undergoing an infant PFT are asleep, they are placed in the equipment with a mask over their mouth and nose. They breath air with oxygen if needed through the mask. Lung volumes and flows are measured while the child breathes through the mask. An inflatable jacket is also placed around the child's chest to help them blow out air.

Learn more about what to expect during an infant PFT (.pdf).

Laryngoscopy and Bronchoscopy

The Pulmonary Function Lab is also responsible for assisting doctors during laryngoscopy and bronchoscopy procedures. These are done in the emergency department or in the hospital in a variety of locations. These procedures involve using a slim scope that directly visualizes the voice box and lungs. Cultures and biopsy specimens can be obtained through the channel of the scope. All scopes are sterilized by the sterile processing department.

  • Laryngoscopy is done by the doctor using a scope to visualize the upper airways.
  • Bronchoscopy includes a laryngoscopy followed by visualizing the lower airways below the vocal cords.