The Connection Between Chronic Obstructive Pulmonary Disease Symptoms and Hyperinflation and Its Impact on Exercise and Function
Section snippets
Limitation of forced expiratory volume in 1 second as a predictor of patient-centered outcomes
Forced expiratory volume in 1 second (FEV1) serves a useful purpose in the diagnosis and physiologic staging of COPD. The progressive decline in FEV1 over time illustrates its utility in disease staging and also correlates with mortality.3 However, FEV1 has limited application in assessing response to bronchodilators or predicting patient-centered outcomes in terms of exercise ability or dyspnea. For example, in the large cohort from the National Emphysema Treatment Trial (NETT), FEV1
Central role of hyperinflation in the pathophysiology of chronic obstructive pulmonary disease
As described above, one of the enigmas of COPD is that baseline FEV1 correlates weakly with patient-centered outcomes. Furthermore, patients with COPD typically present when there has already been a significant decrease in FEV1 accompanied by some degree of hyperinflation and exertional dyspnea. This reinforces the importance of recognizing COPD early, when it might be possible to implement disease-modifying strategies. However, detecting dyspnea early is difficult, because patients tend to
Progression of static hyperinflation in chronic obstructive pulmonary disease
The extent of hyperinflation—or air trapping—depends on the ability to empty the lungs in a satisfactory fashion during an exhalation. Expiratory flow limitation is one of the factors that influences lung emptying and contributes to hyperinflation.11 During the progression of COPD, hyperinflation develops over a long period, just as does the worsening of the airflow obstruction.12, 13 However, the progression of hyperinflation in mild-to-moderate COPD has yet to be studied in detail. It is
Development of dynamic hyperinflation during exercise in chronic obstructive pulmonary disease
Superimposed on static hyperinflation is the phenomenon of exercise-induced hyperinflation, or dynamic hyperinflation, which is particularly dependent on airway caliber. During exercise in healthy individuals, the EELV decreases slightly, and breathing uses part of the expiratory reserve volume. The EILV increases, using part of the inspiratory reserve volume (IRV), and tidal volume (Vt) increases substantially. In patients with COPD, lung emptying is retarded by increased airway resistance and
Clinical evidence of hyperinflation in chronic obstructive pulmonary disease
O’Donnell and colleagues7 studied dynamic hyperinflation in 105 patients with severe COPD (FEV1 of 37% of predicted). They found that EELV increased during exercise, and IC declined by a mean of 0.37 L. EILV approached TLC and, consequently, elastic work of breathing was increased.
Babb and associates15 compared a group of patients with moderate COPD (mean FEV1/FVC of 58% and FEV1 of 72% of predicted) with healthy individuals. While FRC at rest was comparable in the 2 groups at maximal exercise
Evidence for a dyspnea limit related to hyperinflation
Several studies offer evidence of the existence of a dyspnea limit, which seems to occur when EILV approaches within 500 mL of TLC. Interventions that delay the moment when operational lung volumes reach the dyspnea limit by reducing dynamic hyperinflation have been shown to prolong exercise endurance. In a randomized, double-blind, crossover study,17 23 patients with COPD (mean FEV1 of 42% of predicted) received salmeterol or placebo for 2 weeks. Exertional dyspnea tended to improve and its
Exercise testing in chronic obstructive pulmonary disease
The pathophysiology of exercise in COPD is complex because of multiple interlinked abnormalities, including reduced ventilatory capacity, increased work of breathing, skeletal muscle dysfunction due to deconditioning and possibly skeletal muscle apoptosis due to systemic inflammation in advanced disease, and destruction of the pulmonary capillary bed by emphysema. Exercise is traditionally measured by aerobic performance but is more difficult to measure in patients with disability, particularly
Effect of bronchodilators on hyperinflation, exercise performance, and dyspnea
Hyperinflation results from elevated airway resistance, reduced lung recoil, and shortened available expiratory time; these are worsened by exacerbations (which increase airway resistance), exercise (which increases ventilatory requirements), and hypoxemia and anxiety (both of which increase respiratory rate and thereby reduce expiration time). Bronchodilator therapy reduces hyperinflation by decreasing airway resistance and increasing deflation of the hyperinflated lungs. Although dynamic
Effect of other interventions on hyperinflation, exercise performance, and dyspnea
Table 2 summarizes the effects of other interventions such as supplemental oxygen, rehabilitative exercise, helium-oxygen breathing, and lung volume–reduction surgery on hyperinflation, exercise performance, and dyspnea.18, 27, 28, 29, 30, 31, 32, 33 Pulmonary rehabilitation and supplemental oxygen are other interventions that may reduce dynamic hyperinflation by lowering the ventilatory requirements and may improve breathing efficiency during exercise.27, 28 After completing 6 to 8 weeks of
Summary
Limitations of expiratory flow cause air trapping and hyperinflation, which precipitate a cycle of decline that has an adverse impact on patient-centered outcomes, such as dyspnea and activity level. Bronchodilator therapy reduces airway resistance, and pulmonary rehabilitation decreases ventilatory requirements during exercise. In both cases, these changes lead to an improvement in IC, which is indicative of reduced hyperinflation. Importantly, the improvement in IC is associated with a
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