December 06, 2015

Q&A: Evaluation of Lung Function (Pulmonary Function Test)

Evaluation of pulmonary function is important in many clinical situations, both when the patient has a history or symptoms suggestive of lung disease and when risk factors for lung disease are present, such as occupational exposure to agents with known lung toxicity. The European Respiratory Society and the American Thoracic Society have published guidelines for the measurement and interpretation of pulmonary function tests (PFTs).

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In this article:
Pulmonary function tests
MCQ exam: clinical scenario
MCQ exam: answer
MCQ exam: explanation

Pulmonary function tests

The major types of pulmonary function tests (PFTs) are spirometry, spirometry before and after a bronchodilator, lung volumes, and quantitation of diffusing capacity for carbon monoxide. Additional PFTs, such as measurement of maximal respiratory pressures, flow-volume loops, submaximal exercise testing, and bronchoprovocation challenge, are useful in specific clinical circumstances.

In preparation for PFTs, bronchodilator medications are typically held so that bronchodilator response can be assessed after baseline spirometry. As examples, short-acting inhaled bronchodilators (eg, albuterol, salbutamol, ipratropium) should not be used for four hours prior to testing. Long-acting beta-agonist bronchodilators (eg, salmeterol, formoterol) are typically held for 12 hours prior to testing. The ultra long-acting beta agonists (eg, indacaterol, olodaterol, vilanterol) and the long-acting anticholinergic agents glycopyrrolate (glycopyrronium), tiotropium, and umeclidinium are held for 24 hours. Aclidinium would be held for 12 hours, based on twice daily dosing.

MCQ exam: clinical scenario

Which of the following indicates an airflow obstruction in a patient with suspected chronic respiratory failure?

a). A forced expiratory volume in 1 second (FEV1) level >1 L
b). A forced vital capacity (FVC) level >1.5 L
c). A decrease in the FEV1-to-FVC ratio (FEV1/FVC)
d). A reduction in both FEV1 and FVC with a normal FEV1/FVC
e). An increase in both FEV1 and FVC with a normal FEV1/FVC

MCQ questions & answers on medicalnotes.info

MCQ exam: answer

The correct answer is C.

MCQ exam: explanation

Respiratory failure is a syndrome in which the respiratory system fails in one or both of its gas exchange functions: oxygenation and carbon dioxide elimination. In practice, it may be classified as either hypoxemic or hypercapnic. It may be further classified as either acute or chronic. Although acute respiratory failure is characterized by life-threatening derangements in arterial blood gases and acid-base status, the manifestations of chronic respiratory failure are less dramatic and may not be as readily apparent.

Patients with acute respiratory failure generally are unable to perform PFTs; however, these tests are useful in the evaluation of chronic respiratory failure. Normal values for forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC) suggest a disturbance in respiratory control. A decrease in the FEV1-to-FVC ratio (FEV1/FVC) indicates airflow obstruction, whereas a reduction in both FEV1 and FVC and maintenance of FEV1/FVC suggest restrictive lung disease. Respiratory failure is uncommon in obstructive diseases when FEV1 is greater than 1 L and in restrictive diseases when FVC is greater than 1 L.

Reference(s)
1). UpToDate: Overview of pulmonary function testing in adults. Available online: https://www.uptodate.com/contents/overview-of-pulmonary-function-testing-in-adults

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