SHM's Clinical Quick Talks-Pulmonary Function Tests

Pdf Summary

Pulmonary function tests (PFTs) are a group of tests used to assess lung function. They include spirometry, lung volumes, diffusion capacity for carbon dioxide (DLCO), and flow-volume loop. Spirometry measures various lung capacities to diagnose airflow obstruction. Lung volumes are used to diagnose restriction, hyperinflation, and air trapping. DLCO measures gas exchange in the lungs and serves as a marker for functional surface area. The flow-volume loop represents airflow during full inspiration and expiration.<br /><br />In a case study, a 65-year-old man presents with progressive dyspnea. His PFT results show airflow obstruction, restriction, parenchymal disease, and a combined obstructive and restrictive process. A CT scan reveals combined pulmonary fibrosis and emphysema.<br /><br />When interpreting PFTs, a stepwise approach is recommended. Firstly, spirometry is examined for obstruction or restriction. Then, lung volumes are assessed for signs of restriction or hyperinflation. DLCO is analyzed to determine if there is an isolated gas exchange disorder. Lastly, the flow-volume loop is examined for signs of upper airway obstruction.<br /><br />There are several key points to remember. The FEV1/FVC ratio is diagnostic of airflow obstruction, and bronchodilator response can help differentiate asthma from COPD. Low TLC indicates restriction, while high TLC indicates hyperinflation and air trapping. Abnormal DLCO suggests lung disease, and the flow-volume loop can reveal variable extrathoracic obstruction.<br /><br />In conclusion, PFTs provide valuable information about lung function and can aid in diagnosing various respiratory conditions. The FEV1/FVC ratio, TLC, and DLCO are essential for building a differential diagnosis. The flow-volume loop can help identify extra-thoracic obstruction. History is crucial in distinguishing between asthma and COPD. DLCO can assist in differentiating between intra and extra-parenchymal respiratory disorders.

Asset Subtitle

Scott Hagan, Tyler Albert

Keywords

Pulmonary function tests

spirometry

lung volumes

DLCO

flow-volume loop

airflow obstruction

restriction

gas exchange

pulmonary fibrosis

emphysema