Interpreting abnormal PFT patterns
Learn about the various patterns of pulmonary function test abnormalities and how to apply this knowledge when diagnosing disease.
In this video, from our Pulmonary Function Testing Essentials course, you'll learn about the various patterns of pulmonary function test abnormalities and how to apply this knowledge when diagnosing disease.
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Take a deep dive into our Pulmonary Function Testing Essentials course and learn how to apply PFT interpretation guidelines to clinical cases. You'll learn when to use spirometry in your daily clinical practice, what tests to order, and how to interpret results. Complex concepts, like lung volumes, spirometry, diffusing capacity, bronchodilator responsiveness, and obstructive and restrictive patterns, will become second nature to you once you’ve completed this course.
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[00:00:00] Pulmonary function test interpretation rests on comparing individual results with reference or predicted values for large populations of healthy people. The reference population used should have a normal distribution of sex, age, and height, and reflect the ethnic background of the patient population being tested. Traditional pulmonary function test interpretation
[00:00:30] lacks statistical validation and is based on values for FEV1, FVC, and lung volumes greater than 80% predicted, considered as normal. While such methodology is easy to remember and apply, misclassification as normal or abnormal may occur. Even so, this traditional method of classification is still used in general practice.
[00:01:00] For example, the global initiative for obstructive lung disease or GOLD classification scheme for COPD is predicated on this traditional classification. More recently, guidelines have been developed, which are supported by statistical rigor in their application. The guidelines recommend that in the United States, for example, reference equations from the National Health and Nutrition
[00:01:30] Survey III or NHANES III be used and that individual pulmonary function test results be considered abnormal if the patient falls below the fifth percentile of the reference population. Broadly speaking, interpretation of pulmonary function test begins with recognition of major categories of pathophysiologic abnormalities, as an obstructive pattern or restrictive pattern or both.
[00:02:00] An obstructive pattern, usually due to airway narrowing anywhere from the upper airway to the small peripheral bronchioles, is characterized by reduced airflow rates with the reduction in the ratio of FEV1 to vital capacity. Commonly, an elevation in lung volumes, particularly TLC, may also be noted. On the other hand, a restrictive pattern is
[00:02:30] characterized by a limitation in lung or chest wall expansion and is manifest as a reduced vital capacity, preserved FEV1 to FVC ratio, and reduced lung volumes. Some disease states may produce both obstructive and restrictive findings, constituting a so called combined or mixed pattern. Finally, a reduction in gas transfer may be seen as
[00:03:00] part of either an obstructive or restrictive pattern or as an isolated finding. Using the traditional method, the following rules are generally applied. An FEV1 over FVC of less than 70% implies airway obstruction. An FEV1 over FVC of 70% or greater, along with reduced lung volumes, especially TLC to less than
[00:03:30] 80% predicted, indicates restriction. As an example of use of this system in classifying lung disease, let's consider the GOLD classification of airflow limitation in COPD. The global initiative for obstructive lung disease or GOLD classification uses defined cutoffs as part of its classification scheme. In particular, in evaluating the
[00:04:00] severity of obstructive airways disease, which itself is defined as a post-bronchodilator FEV1 to FVC ratio of less than 0.7. Mild disease or GOLD 1 is an FEV1 greater than 80% predicted. Moderate obstructive disease or GOLD 2 is an FEV1 greater than or equal to 50% but less than 80%
[00:04:30] predicted. Severe obstruction or GOLD 3 is an FEV1 greater than or equal to 30% but less than 50% predicted. In very severe obstruction or GOLD 4 is an FEV1 less than 30% predicted.