How is lung function measured?

A test called spirometry may be done in your doctor's office. It allows your doctor to measure your lung function. 
Lauren Goode, MD
Internal Medicine
Many tests of lung function have been developed, and each provides slightly different information about how well your lungs are working. Lung function tests are painless, noninvasive and performed using a machine called a spirometer. By breathing into the spirometer, your doctor can measure your lung volume and your ability to move air in and out of your lungs in a certain period of time. Your results are compared with typical findings of a healthy person your age and height. Your doctor can then determine to what extent your lung function is diminished.

Pulmonary function measures include:
  • Pulse oximetry: This test uses a sensor on your finger to get basic information about the amount of oxygen in your blood.
  • Forced vital capacity (FVC): This is the maximum volume of air that can be forcibly exhaled after inhaling as deeply as possible.
  • Residual volume (RV): The amount of air that remains in the lungs when measuring vital capacity after a maximal exhalation. In persons with chronic obstructive pulmonary disease (COPD), for instance, RV is usually increased dramatically from normal because air is trapped in the damaged lung and cannot be exhaled normally.
  • Total lung capacity: The total amount of air the lungs are capable of holding. It is the combination of FVC and RV.
  • Forced expiratory volume in one second (FEV1): The volume of air that can be forcibly exhaled in one second. It represents the rate of air movement out of the lungs. FEV1 typically declines a very small amount per year in normal persons. But, the decline can be several times greater in people with COPD, for example.
  • Peak expiratory flow (PEF): This is the maximum speed of exhalation after maximal inhalation.
  • Carbon monoxide diffusing capacity: This test measures how well your lungs transfer a small amount of carbon monoxide gas into your blood.
  • Arterial blood gas: This test analyzes the amount of oxygen and carbon dioxide in your bloodstream.

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