How Spirometry Is Used to Diagnose and Manage Asthma

What You Need to Know About Spirometry and Your Asthma

What Is Spirometry?

Spirometry measures both how much and how fast air moves through your lungs. It's is much more reliable than peak flows and spirometers are required to meet certain standards from the American Thoracic Society. Depending on which specific tests are ordered, spirometry may take anywhere from 10 to 30 minutes.

From the patient perspective, spirometry is similar to a peak flow except:

  • It is performed in a doctor's office
  • A machine called a spirometer, collects data as you maximally inhale and forcefully exhale

Why Would My Asthma Provider Order Spirometry?

Spirometry may be useful to your asthma care provider in the following situations. Spirometry:

  • Cannot by itself diagnose asthma, but may help your asthma care provider make an asthma diagnosis
  • Aids in asthma management
  • Helps monitor the progression of your asthma over time

Spirometry results cannot be considered alone, but will help support or exclude your asthma diagnosis. After taking a thorough history and performing a physical exam, spirometry may help establish an asthma diagnosis. Over time, spirometry measurements will indicate if your asthma is getting better or worse.

What Does Spirometry Measure?

Spirometry allows your asthma care provider to measure several aspects of your lung function that are important in determining both the severity and control of your asthma including:

How is Spirometry Preformed?

Spirometry is performed with a device called a spirometer. It consists of a mouthpiece that is connected via tubing to a machine that records results and displays them graphically as you breathe in and forcefully exhale.

In order to perform spirometry, a technician will ask you to:

  1. Apply a nose clip to prevent you from exhaling through the nose
  2. Have you breathe normally for a short time and then
  3. Inhale as deeply as possible
  4. Closes their mouth tightly around the tube and
  5. Exhale forcefully and completely through the mouthpiece for as long as possible while maintaining a tight seal around the mouthpiece

Spirometry will often be repeated three times to get your best and maximum effort. Your provider may also repeat the test after having you take a short-acting bronchodilator like Albuterol.

What Do My Spirometry Results Mean?

Your FEV1 value expressed as a percentage of predicted can be used to classify the amount of obstruction occurring with your asthma:

  • FEV1 greater 80% of predicted= normal
  • FEV1 60% to 79% of predicted = Mild obstruction
  • FEV1 40% to 59% of predicted = Moderate obstruction
  • FEV1 less than 40% of predicted = Severe obstruction

Alternatively, if your doctor is unsure if you have asthma, an improvement in your FEV1 of 12% or more with a rescue medication helps your asthma care provider confirm a diagnosis.

Is Home Spirometry An Option?

There are a number of reasons why you might want to consider home spirometry.

Some patients just want more information than a peak flow can give and are willing to put in the effort to understand what the numbers mean. For people who are uninsured or underinsured, spirometry may be just too expensive. Others may not have access to a specialist performing the procedure or cannot travel the distances required.

With improvements in technology, home spirometry has increasingly become accepted by the medical community. There are a number of benefits. If you are performing the test at home it is not only more convenient, but you can more regularly test and share information with your doctor.

As a result, you may be able to catch trends not involved in your current asthma monitoring and make the appropriate changes or get appropriate testing. When part of a well thought out asthma action plan, both outcomes and costs may be decreased.

However, a number of challenges still remain. The spirometers are expensive and you will need a significant amount of training to use one. Additionally, there are a number of different models available on the market. Your doctor may not connect to your particular model. I see this commonly with diabetes monitors. There are at least several dozen monitors with their own software and doctors do no want to have to interact with each one-- so check with your doctor. Additionally, if next year your insurance changes or your doctor moves out of town, your new doctor may not use.

To address some of these concerns, investigators at the University of Wisconsin have developed SpiroSmart- a smartphone-enabled app that allows for the testing of some pulmonary function tests. SpiroSmart has you hold your smartphone about an arm’s length away, take a deep breathe, and then forcefully exhale at your phone screen until you are not able to exhale anymore. Your phone’s microphone makes a recording and the data is sent to a server that calculates the flow rates. Their research demonstrated that flow rates were calculated to within 5% of those measured with in-office spirometry.

What Problems Are You having With Your Asthma?

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National Heart, Lung, and Blood Institute. Accessed: January 1, 2009. Expert Panel Report 3 (EPR3): Guidelines for the Diagnosis and Management of Asthma

Clinical Pulmonary Function Testing, Exercise Testing, and Disability Evaluation. In Chest Medicine: Essentials Of Pulmonary And Critical Care Medicine. Editors: Ronald B. George, Richard W. Light, Richard A. Matthay, Michael A. Matthay. May 2005, 5th edition.

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