What is the hallmark of obstructive defects in spirometry for pulmonary function testing?

Updated: May 14, 2020
  • Author: Kevin McCarthy, RPFT; Chief Editor: Nader Kamangar, MD, FACP, FCCP, FCCM  more...
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Disproportionate reduction in the FEV1 as compared with the FVC is reflected in the FEV1/FVC ratio and is the hallmark of obstructive lung diseases. This physiologic category of lung diseases includes but is not limited to asthma, acute and chronic bronchitis, emphysema, bronchiectasis, cystic fibrosis, and bronchiolitis. The forced expiratory flow at any given lung volume is reduced. The mechanism responsible for the reduction in airflow can be bronchial spasm, airway inflammation, increased intraluminal secretions, and/or reduction in parenchymal support of the airways due to loss of lung elastic recoil. Poor understanding and effort on the part of the patient is also a cause for reduced flows, and the diagnosis of airway obstruction should be limited to measurements composed of acceptable efforts demonstrating repeatability of FVC and FEV1.

The use of a fixed lower limit of normal for the FEV1/FVC ratio as proposed by the Global Initiative for Obstructive Lung Disease (GOLD) lacks a scientific basis and results in significant misclassification of patients at either end of the age spectrum. Young patients are classified as "normal" when airflow obstruction is present, and older patients are classified as showing obstruction when no airflow obstruction is present. The use of the GOLD threshold for identifying airway obstruction should be discouraged in clinical practice where or when computerized predicted values are available.

The recommended practice for identifying a spirometric abnormality is to use the predicted lower limit of normal for that individual based on the sex, age, height, and ethnicity. The GLI reference equations provide lower limits of normal for spirometric parameters.

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