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What Is A Spirometry Evaluation

Updated on November 20, 2011

A spirometry evaluation, also called a pulmonary function test, is the first, most basic test that physicians use to measure your lung function. If you have asthma, severe allergies, or COPD, you are probably already familiar with this test.

A spirometry evaluation effectively determines your lungs’ ability to take in, hold, and properly use the air you breathe. The test is done with a device called a spirometer, and it involves taking a deep breath, and exhaling into the spirometer as completely, and with as much force as possible.

How Is A Spirometry Test Conducted

A spirometry test is usually done with the patient standing upright. You'll be given a spirometer with a sterile tube and mouthpiece, and you may be asked to wear a nose plug to prevent air from escaping during the test.

When the technician tells you to, you will inhale deeply to completely fill your lungs with air, then exhale as forcefully as you can, and for as long as possible. At the end of the exhalation, you will inhale as sharply as you can. As you do this, the spirometer measures and records both the volume and speed of the air passing through its chamber, and several other factors. The test is usually repeated two or three times to establish an average. The spirometry test is quick and painless, and the spirometer itself can be as simple as a simple plastic tube with a gauge or meter, or as complex as a full electronic machine with computer readout.

Typical Spirometer
Typical Spirometer

Why Would I need A Spirometry Evaluation

There are several reasons that your doctor might order a spirometry test. Among them are:

  • To determine the severity of a lung disease
  • To monitor the progression of a lung disease
  • To determine whether a lung disease is restrictive (decreasing air flow) or obstructive (disrupting air flow)
  • To monitor the effectiveness of your treatment

What Does A Spirometry Exam Actually Measure

There are several values, or parameters, that a spirometry test measures. The most common is called Forced Vital Capacity (FVC). Measured in liters, FVC is the volume of air the patient can blow through the spirometer while completely emptying their lungs.

Another common parameter is Forced Expiratory Volume over 1 second (FEV1). This is also commonly measured over 2 second and 3 second durations. FVC and FEV1 results are also often combined and expressed as a ratio.

FVC, FEV1, and the FEV1/FVC ratio are the most common measurements in a spirometry evaluation, but there are several other important results which include:

Forced Expiratory Flow (FEF): A measurement of the air you exhale during the middle portion of the test.

Forced Inspiratory Flow (FIF): Similar to FEF, but this measurement is taken as you inhale.

Peak Expiratory Flow (PEF): Is the maximum velocity, measured in liters per minute, at which the air exits your lungs as you forcibly exhale.

Tidal Volume (TV): This is the total volume of air that you inhale and then exhale during normal breathing.

Total Lung Capacity (TLC): TLC is the total volume of air in your lungs.

Bronchial Challenge Test

Spirometry is sometimes used as part of a more in depth study, called a Bronchial Challenge Test. In this case, the spirometry test is done after the patient inhales a nebulized dose of methacholine or histamine, which are both broncho restrictors (narrowing the airway). Some doctors refer to this test as a Methacholine Challenge test or a Histamine Challenge test.

The goal of the Bronchial Challenge test is to determine the degree of narrowing of the airway. This helps doctors determine the proper medication and dosage for a patient's specific needs.

Sometimes the spirometry test is repeated after the patient inhales a nebulized broncodilator (opening the airway). This is called a reversibility test, and is helpful in allowing the doctor to distinguish asthma from Chronic Obstructive Pulmonary Disease (COPD).

The Bronchial Challenge test is physically demanding. In severe cases it can result in violent, uncontrolled coughing, which make it nearly impossible to complete. The Bronchial Challenge test is not usually ordered for patients with severe airway obstruction.

Spirometry Test Results Interpretation

Since normal values vary from one person to the next, spirometry test results are usually measured against an average, based upon what doctors would expect to see in people that have similar stature, age, gender and race. While there are different ranges for each of the spirometry test parameters, if your numbers are below 85% of the average set by the National Heart, Lung And Blood Institute, you will probably be referred for additional testing.


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