The Role of Pulmonary Function Testing in the Diagnosis and Management of COPD

Abstract

Pulmonary function testing (PFT) has a long and rich history in the definition, diagnosis, and management of COPD. For decades, spirometry has been regarded as the standard for diagnosing COPD; however, numerous studies have shown that COPD symptoms, pathology, and associated poor outcomes can occur, despite normal spirometry. Diffusing capacity and imaging studies have called into question the need for spirometry to put the "O" (obstruction) in COPD. The role of exercise testing and the ability of PFTs to phenotype COPD are reviewed. Although PFTs play an important role in diagnosis, treatment decisions are primarily determined by symptom intensity and exacerbation history. Although a seminal study positioned FEV₁ as the primary predictor of survival, numerous studies have shown that tests other than spirometry are superior predictors of mortality. In years past, using spirometry to screen for COPD was promulgated; however, this only seems appropriate for individuals who are symptomatic and at risk for developing COPD.

Keywords: chronic obstructive; diagnosis; exercise test; pulmonary diffusing capacity; pulmonary disease; respiratory function tests; spirometry.

Fig. 1.

FEV₁/FVC as a function of age in never-smoking women. The ∼20° angle line represents the statistical lower limit of normal, and the horizontal line represents the 70% fixed threshold of normality. The light gray triangle depicts potential false-negative results in younger adults, whereas the darker triangle depicts potential false-positive results in older adults when the fixed 70% threshold is applied. From Reference 18, with permission.

Fig. 2.

Kaplan-Meier plots of first hospitalization related to COPD according to Global Initiative for Obstructive Lung Disease (GOLD) severity classification according to FEV₁. GOLD severity classifications 1–3 are divided based on whether FEV₁/FVC is below the statistical lower limit of normal. Subjects classified as GOLD 0 and GOLD 1–3 with FEV₁ < 0.7 but > lower limit of normal had a higher risk of a first COPD hospitalization than did normal subjects. LLN = lower limit of normal. From Reference 18, with permission.

Fig. 3.

COPD-free survival in smokers with normal spirometry. Subjects with a post-bronchodilator FEV₁/SVC < 0.7 were more likely to progress to spirometry-defined COPD. SVC = slow vital capacity. From Reference 26, with permission.

Fig. 4.

Four characteristics used to make a COPD diagnosis from the COPDGene 2019 redefinition of COPD. From Reference 70, with permission.

Fig. 5.

Hyperpolarized helium 3 (³He) static ventilation and apparent diffusion coefficient images from former smokers with normal spirometry and normal diffusion capacity, normal spirometry and abnormal diffusion capacity, and subjects with GOLD I COPD. The subjects with abnormal diffusion capacity had worse ³He images than did the subjects with normal diffusion, which suggests early emphysema, despite normal thoracic computed tomography. GOLD = Global Initiative for Obstructive Lung Disease. From Reference 75, with permission.

Fig. 6.

The mean percent of predicted FEV₁, maximum O₂ uptake (V̇_O2), and inspiratory capacity based on poor communicating fraction tertiles. Adapted from Reference 79.

Fig. 7.

The inverse relationship between mortality and 6-min walk distance (6MWD) in subjects with severe COPD. From Reference 121, with permission.

Fig. 8.

Progressive reduction of inspiratory reserve volume (IRV) and increase in end-expiratory lung volume (EELV) due to dynamic hyperinflation (DH) during exercise in a subject with COPD. TLC = total lung capacity; EILV = end-inspiratory lung volume. From Reference 154, with permission.

Fig. 9.

Cumulative survival over months of follow-up of subjects with GOLD I COPD and different levels of diffusion capacity ( ${\mathrm{D}}_{\text{LCO}}$) impairment. pred = predicted. From Reference 193, with permission.