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Commentary on Spirometry

Dr. Tom

Many questions have been asked about spirometry, a test that measures your ability to fill and empty the lungs, and I’d like to take this opportunity to explain the basics of spirometry.

I often recommend spirometry for my patients, and spirometry should be done on:

  • All current or former smokers, age 45 or older.
  • Anyone with shortness of breath on light exercise, chronic cough, wheeze, or excess mucus.

Often long lists of numbers are reported in the Ask Dr. Tom questions, but in reality there are only two numbers that have clinical meaning.

FVC: Forced Vital Capacity, measures the total volume of air you can forcefully blow out.

FEV1: Forced Expiratory Volume in One-Second, measures the flow of air that you can blow out in the first second of exhalation. Typically FEV1 is considered “normal” if greater than 80% of predicted. FEV1 is reduced in both obstructive and restrictive lung disease.

Also the FEV1/FVC ratio is important.

Normal FEV1/FVC is >70%.

Lower than this means airflow obstruction. In those with severe obstructive airway disease, the FEV1/FVC can be as low as 40-50%.

Much higher, i.e. > 80%, suggests lung restriction from scarring processes.

Neither you nor your doctor should pay any attention to all those other numbers, which I call “nonsense numbers.” Now, not everyone who reads this will agree with my interpretation of spirometry, but it is the consensus of pulmonary experts.

Keep it simple, and understand the value of spirometry. The National Lung Health Education Program is an organization that is dedicated to educating doctors and patients in early identification and treatment of lung disease through the use of spirometry and their motto is  “Test Your Lungs, Know Your Numbers.”  This is good advice, you should know your test results and keep track of your spirometry numbers (FVC, FEV1, and FEV1/FVC) and remember to keep it simple.

All doctors who take care of pulmonary patients should have a simple, inexpensive spirometer in their office, and use it regularly. There is no need to go to a pulmonary function laboratory for other tests, unless a pulmonologist, allergist, or experienced internist recommends this and can interpret the results.

Dr. Tom

2024American Association for Respiratory Care