BACKGROUND
 
This is the first of a series of concise manuscripts focused on how best to use the pulmonary function laboratory for diagnosis, assessment of disease severity/risk estimation, and selection of treatment strategies in prevalent respiratory and nonrespiratory diseases. We start with a heterogeneous lung disease in which pulmonary function tests (PFTs) assume a pivotal role in each of these domains: COPD.(1)
 
OVERVIEW
 
A 61-year-old man with a smoking history of 21 pack-years was referred to Respirology because of “out-of-proportion” dyspnea (modified Medical Research Council dyspnea scale [mMRC] score = 2-3) relative to preserved FEV1 and FEV1/FVC ratio, and a non-significant volume (FVC) response to short-acting bronchodilator. Given the nonobstructive findings on spirometry and lack of improvement after treatment with two different long-acting muscarinic antagonists (LAMAs), the referring physician was uncertain of the diagnosis of COPD. Repeat PFTs showed low FEF25-75%, “scooping” of the expiratory flow-volume curve at low lung volumes, low inspiratory capacity (IC), a mild but consistent increase in residual volume and functional residual capacity (either absolute or relative to TLC), increased specific airway resistance, low DLco, and low alveolar volume/TLC. Cardiopulmonary exercise testing showed excess ventilation and dynamic hyperinflation leading to inspiratory constraints and limiting dyspnea. COPD was confirmed, and treatment was escalated to dual therapy with long-acting β2 agonist (LABA)/LAMA. A two-month course of dual LABA/LAMA therapy was associated with improvement in dyspnea (mMRC score = 1), allowing the patient to enroll in a structured reconditioning exercise program.
 
Regrettably, the role of PFTs in COPD management has been progressively devalued in influential guidelines. The 2023 GOLD report, for instance, confirms previous versions by recommending forced spirometry for diagnosis only.(2) Despite suggesting the grading of FEV1 impairment, little emphasis is given to its use (or to the use of any other functional marker) in treatment choices. Simply sticking to a rigid FEV1/FVC cutoff for diagnosis can lead to misinterpretation, requiring careful individualization.(3) Findings of decreased available volume for tidal expansion (i.e., low IC) and/or increased “static” lung volumes give unique insights into the genesis and severity of COPD-related dyspnea. There is a large variability in key determinants of breathlessness at a given FEV1: the severity of lung mechanical impairment (as determined by measurements of lung volumes) and gas exchange inefficiency (as assessed by DLco and carbon monoxide transfer coefficient) is much more informative.(4) As depicted in Chart 1, this knowledge may have important implications for pharmacological and nonpharmacological treatment. Simple tests of functional exercise capacity, such as the six-minute walk test, might prove useful in quantifying patient impairment, in determining the potential need for exertional oxygen supplementation, and in prognostic estimation in multiparametric indexes. As shown herein, incremental cardiopulmonary exercise testing might indicate that “the lungs” do contribute to exertional dyspnea, thereby prompting treatment optimization in equivocal cases.(5)

 

 
CLINICAL MESSAGE
 
It is unlikely that the clinical and surgical management of COPD will ever dispense with functional data. The pulmonologist should combine the information provided by PFTs with clinical data (e.g., dyspnea severity, exacerbation burden), blood workup data (e.g., eosinophil count, IgE and alpha-1 antitrypsin levels), and structural findings (e.g., emphysema burden and distribution, airway disease) to decide on the best clinical or surgical treatment approaches (Chart 1).
 
AUTHOR CONTRIBUTIONS
 
All authors contributed to conceptualization, writing, review, and editing.
 
CONFLICTS OF INTEREST
 
None declared.
 
REFERENCES
 
1.            Neder JA, de-Torres JP, Milne KM, O’Donnell DE. Lung Function Testing in Chronic Obstructive Pulmonary Disease. Clin Chest Med. 2020;41(3):347-366. https://doi.org/10.1016/j.ccm.2020.06.004
2.            Global Initiative for Chronic Obstructive Lung Disease (GOLD). Bethesda: GOLD; c2023 [cited 2023 May 1]. Global strategy for the diagnosis, management and prevention of Chronic Obstructive Pulmonary Disease: 2023 report. Available from: https://goldcopd.org/2023-gold-report-2
3.            Neder JA. Functional respiratory assessment: some key misconceptions and their clinical implications. Thorax. 2021;76(7):644-646. https://doi.org/10.1136/thoraxjnl-2020-215287
4.            Neder JA, Berton DC, O’Donnell DE. The Lung Function Laboratory to Assist Clinical Decision-making in Pulmonology: Evolving Challenges to an Old Issue. Chest. 2020;158(4):1629-1643. https://doi.org/10.1016/j.chest.2020.04.064
5.            O’Donnell DE, Milne KM, Vincent SG, Neder JA. Unraveling the Causes of Unexplai-ned Dyspnea: The Value of Exercise Testing. Clin Chest Med. 2019;40(2):471-499. https://doi.org/10.1016/j.ccm.2019.02.014