What is spirometry?

Updated: May 14, 2020
  • Author: Kevin McCarthy, RPFT; Chief Editor: Nader Kamangar, MD, FACP, FCCP, FCCM  more...
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Spirometry assesses the integrated mechanical function of the lung, chest wall, respiratory muscles, and airways by measuring the total volume of air exhaled from a full lung (total lung capacity [TLC]) to maximal expiration (residual volume [RV]). This volume, the forced vital capacity (FVC) and the forced expiratory volume in the first second of the forceful exhalation (FEV1), should be repeatable to within 0.15 L upon repeat efforts in the same measurement unless the largest value for either parameter is less than 1 L. In this case, the expected repeatability is to within 0.1 L of the largest value. The patient is instructed to inhale as much as possible and then exhale rapidly and forcefully for as long as flow can be maintained. The patient should exhale until one of the criteria defining the end of a forced exhalation has been reached. At the end of the forced exhalation, the patient should again inhale fully as rapidly as possible. The FVC should then be compared with that inhaled volume to verify that the forced expiratory maneuver did start from full inflation.

Reduction in FEV1 may reflect reduction in the maximum inflation of the lungs (TLC); obstruction of the airways; respiratory muscle weakness; or submaximal expiratory force due to poor coaching, poor understanding, or malingering. Airway obstruction is the most common cause of reduction in FEV1. Airway obstruction may be secondary to bronchospasm, airway inflammation, loss of lung elastic recoil, increased secretions in the airway, or any combination of these causes. Response of FEV1 to inhaled bronchodilators is used to assess the reversibility of airway obstruction, although it is now widely appreciated that a response showing a lack of a significant increase in FEV1 does not indicate the patient will not benefit clinically from bronchodilator therapy. A significant increase in the inspiratory capacity (IC) and/or vital capacity (VC) after bronchodilator therapy can occur even when the FEV1 fails to show a significant change. [1]

The standards used to describe the quality of spirometry measurements are from the Standardization of Spirometry 2019 Update. [2]  This document provides examples of the most common technical problems associated with spirometry testing. See Standardization of Spirometry 2019 Update. An Official American Thoracic Society and European Respiratory Society Technical Statement for more information.

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