Activity restriction in mild COPD: a challenging clinical problem

Abstract

Dyspnea, exercise intolerance, and activity restriction are already apparent in mild chronic obstructive pulmonary disease (COPD). However, patients may not seek medical help until their symptoms become troublesome and persistent and significant respiratory impairment is already present; as a consequence, further sustained physical inactivity may contribute to disease progression. Ventilatory and gas exchange impairment, cardiac dysfunction, and skeletal muscle dysfunction are present to a variable degree in patients with mild COPD, and collectively may contribute to exercise intolerance. As such, there is increasing interest in evaluating exercise tolerance and physical activity in symptomatic patients with COPD who have mild airway obstruction, as defined by spirometry. Simple questionnaires, eg, the modified British Medical Research Council dyspnea scale and the COPD Assessment Test, or exercise tests, eg, the 6-minute or incremental and endurance exercise tests can be used to assess exercise performance and functional status. Pedometers and accelerometers are used to evaluate physical activity, and endurance tests (cycle or treadmill) using constant work rate protocols are used to assess the effects of interventions such as pulmonary rehabilitation. In addition, alternative outcome measurements, such as tests of small airway dysfunction and laboratory-based exercise tests, are used to measure the extent of physiological impairment in individuals with persistent dyspnea. This review describes the mechanisms of exercise limitation in patients with mild COPD and the interventions that can potentially improve exercise tolerance. Also discussed are the benefits of pulmonary rehabilitation and the potential role of pharmacologic treatment in symptomatic patients with mild COPD.

Keywords: chronic obstructive pulmonary disease (COPD); dyspnea; exercise; physical activity; small airway dysfunction.

Figure 1

Characterization of mild chronic obstructive pulmonary disease. Abbreviations: NS, nervous system; V/Q, ventilation/perfusion.

Figure 2

Ventilatory insufficiency in mild chronic obstructive pulmonary disease. V’_E/V’CO₂ (left) and PETCO₂ (right) in response to symptom-limited incremental cycle exercise in patients with mild COPD and healthy controls (Mean ± SE) at rest, 20, 40, 60, and 80 watt during exercise and at peak exercise (*P<0.05) COPD versus control at a standardized work rate (watt). Reprinted with permission of the American Thoracic Society. Copyright © 2013 American Thoracic Society. Ofir D, Laveneziana P, Webb KA, Lam YM, O’Donnell DE. Mechanisms of dyspnea during cycle exercise in symptomatic patients with GOLD stage I chronic obstructive pulmonary disease. Am J Respir Crit Care Med. 2008;177(6):622–629. Official Journal of the American Thoracic Society. Abbreviations: V’_E, minute ventilation; V’_E/V’CO₂, ventilatory equivalent for carbon dioxide; PETCO₂, partial pressure of end-tidal carbon dioxide; PaCO₂, arterial partial pressure of carbon dioxide; VD, dead space volume; VT, tidal volume; V’CO₂, carbon dioxide output; COPD, chronic obstructive pulmonary disease.

Figure 3

Operating lung volumes during exercise. Note: Data from Ofir D, Laveneziana P, Webb KA, Lam YM, O’Donnell DE. Mechanisms of dyspnea during cycle exercise in symptomatic patients with GOLD stage I chronic obstructive pulmonary disease. Am J Respir Crit Care Med. 2008;177(6):622–629. Official Journal of the American Thoracic Society. Abbreviations: COPD, chronic obstructive pulmonary disease; EELV, end-expiratory lung volume; IC, inspiratory capacity; IRV, inspiratory reserve volume; ISO-V’_E, isotime minute ventilation; TLC, total lung capacity; VT, tidal volume.

Figure 4

Exertional dyspnea intensity Notes: Values are means ± standard error of the mean. Mild > normal slopes (P<0.05) Adapted with permission of the American Thoracic Society. Copyright © 2013 American Thoracic Society. Ofir D, Laveneziana P, Webb KA, Lam YM, O’Donnell DE. Mechanisms of dyspnea during cycle exercise in symptomatic patients with GOLD stage I chronic obstructive pulmonary disease. Am J Respir Crit Care Med. 2008;177(6): 622–629. Official Journal of the American Thoracic Society; Borg Scale. Abbreviations: GOLD, Global initiative for chronic Obstructive Lung Disease; V’O₂, oxygen consumption.