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Functional respiratory assessment: some key misconceptions and their clinical implications
  1. José Alberto Neder
  1. Department of Medicine, Queen's University, Kingston, ON, Canada
  1. Correspondence to Professor José Alberto Neder, Division of Respirology, Department of Medicine, Queen's University, Kingston, ON K7L 2V7, Canada; alberto.neder{at}queensu.ca

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Dear editors,

There are few specialties in which the functional evaluation assumes the same pivotal role as in respiratory medicine. Although the patterns of abnormalities exposed by pulmonary function tests are not pathognomonic, they are frequently helpful to narrow the diagnostic alternatives. In the right clinical context, the absence of functional abnormality might be reassuring. Testing results can provide useful information for the longitudinal assessment of patients with known respiratory diseases; moreover, they might have an auxiliary role on risk stratification and prognosis estimation. Unfortunately, there has been a progressive abandonment of applied respiratory physiology in favour of basic sciences and molecular medicine. Accordingly, controversial issues on pulmonary function tests interpretation are much less discussed nowadays compared with a few decades ago. It should also be recognised that some key concepts in the interpretation of spirometry, ‘static’ lung volumes and cardiopulmonary exercise testing are still based on physiological constructs rather than evidence from prospective trials. With the intent of igniting some critical reflections on the current role of the laboratory of lung function tests on clinical decision making in our field, I herein challenge some deeply entrenched interpretative beliefs. They have been selected based on our long-standing interaction with learners and seasoned pulmonologists. In each scenario, I discuss the reasons why a given statement might be misleading, and the potential clinical consequences of testing misinterpretation. If feasible, I suggest some strategies to avoid the underlying pitfalls.

Normal forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) ratio rules out obstructive airway disease

There is little disagreement that, in the right clinical context, a FEV1/FVC ratio <the lower limit of normal (LLN) rules in obstruction (though, by definition, 5% of normal subjects have an FEV1/FVC ratio <LLN). However, if the small airways close precociously during the forced expiratory manoeuvre in a subject with airway disease, FVC might decrease more (or to the same …

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Footnotes

  • Contributors The author has the original idea of the manuscript. JAN wrote the manuscript.

  • Funding The author has not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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