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For Patients - Pulmonary Studies

A Complete Pulmonary Function Test is actually a series of breathing tests conducted at one visit. The separate tests may vary depending on your diagnosis, but are typically:
  • Spirometry
  • Lung Volumes
  • Diffusing Capacity (DLCO)
  • Oximetry
  • Six Minute Walk Test
Spirometry

Spirometry measures the amount of air a person can breathe in and out as well as the speed of air movement to and from the lungs. Several different maneuvers are usually performed:

The Forced Vital Capacity (FVC) requires you to take a deep breath and blow into a tube as hard and long as you can (like blowing a trumpet.) This is a sensitive test for obstructive lung disease like asthma or emphysema. The Maximal Voluntary Ventilation (MVV) requires you to huff and puff through a mouthpiece, breathing as much as you can for about 10 seconds. This procedure measures lung flexibility and muscle strength.

These procedures are usually repeated several times after a short rest, to assure consistency and accuracy. These tests take only a few minutes each, and may be repeated after the use of an inhaled medication (bronchodilator) to test for the presence of asthma.

Lung Volumes

The amount of air that your lungs can hold cannot be measured simply by blowing out. Instead, it must be measured indirectly by one of two methods:

Body Box (Plethysmograph) – In this procedure, you sit in a Plexiglas box about the size of a telephone booth and breathe in and out through a small mouthpiece. On the technologist’s prompt, you pant like a puppy for 2 or 3 seconds while the box is closed. With the help of data from the spirometry test (below), the instrument instantly calculates your lung volume.

The Nitrogen Washout Test uses simpler equipment, but gives the same results. By breathing pure oxygen through a mouthpiece, all the nitrogen in your lungs (normal air is 78% nitrogen) is replaced with oxygen. The system measures the amount of gas removed and calculates lung size from this data. The test takes no more than seven minutes.

Diffusing Capacity (DLCO)

The DLCO tests the ability of air to cross through your lungs and into your blood stream without actually drawing any blood. After taking a deep breath of normal air mixed with a tiny bit of harmless but rare gas, you are asked to hold your breath for ten seconds. After you exhale, this test determines how much of the rare gas passed into your blood, indicating how well oxygen gets in and carbon dioxide gets out. The DLCO test is very helpful in differentiating emphysema from other obstructive diseases.

Oximetry

An approximation of your blood’s oxygen content can be made with a small plastic finger clip that measures the absorption of light through your fingernail. Oxygenated blood is much redder than non-oxygenated blood, and this device can instantly determine the percentage of oxygen saturation in your blood stream (it also determines your pulse.) The test takes only seconds and is painless and harmless.

This test may also be done while you are walking, to determine if your oxygen levels drop significantly with exercise.

Six Minute Walk Test

The Six Minute Walk Test is an indication of your level of fitness and degree of shortness of breath. You will be asked to walk back and forth along a pre-measured pathway while a technologist monitors your heart rate, blood oxygen level, blood pressure and level of fatigue. The distance you walk in the time allowed and your body's response to the exercise indicate the fitness of your lungs.

This test is usually performed separately from a Complete Pulmonary Function Study.
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