Practical Pearls from the GOLD Guidelines on COPD

By Juan Garcia, MD, FCCP; and Stephen Jenkinson, MD, FCCP

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Evaluating Pulmonary Function

COPD is diagnosed by a combination of history and physical examination and the use of objective measurement of airway obstruction. The standard pulmonary function test used to measure airway obstruction is the forced expiratory spirogram. This test is useful in the evaluation of patients presenting with symptoms of COPD by providing measurements of FEV₁, FVC, and the ratio of FEV₁/FVC (which is also called the timed vital capacity). The FVC provides a measure of lung volume, and the FEV₁ and FEV₁/FVC provide a measure of obstruction. In most of these patients, other abnormal lung volumes that may exist include increases in both the total lung capacity and the residual volume. These increases in lung volumes are due to hyperinflation of the lungs.⁶

Pearl: In patients with emphysema, the specific diffusing capacity for carbon monoxide (corrected for lung volume) is often markedly decreased.

Pearl: Another pulmonary function test that can be useful in diagnosing COPD includes the maximum expiratory flow volume curve, which shows a decrease in the flow rates during the latter portion of the maximum expiratory flow volume curve which is effort independent. Flow depends on the resistance of the peripheral bronchi and the recoil pressure of the lung in the mid-vital capacity range.

Pearl: Healthy nonsmokers begin losing lung function after age 35 at a rate of about 30 mL/yr. The rate of lung function deterioration in patients who have begun to develop COPD rises to 50 to 100 mL/yr, and may have even greater declines when they have experienced exacerbations of their disease.⁷

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