Ventilatory constraints and dyspnea during exercise in chronic obstructive pulmonary disease

Abstract

Dyspnea (respiratory difficulty) and activity limitation are the primary symptoms of chronic obstructive pulmonary disease (COPD) and progress relentlessly as the disease advances, contributing to reduced quality of life. In COPD, the mechanisms of dyspnea are multifactorial, but abnormal dynamic ventilatory mechanics are believed to play a central role. In flow-limited patients with COPD, dynamic lung hyperinflation (DH) occurs during exercise and has serious sensory and mechanical consequences. In several studies, indices of DH strongly correlate with ratings of dyspnea intensity during exercise, and strategies that reduce resting hyperinflation (either pharmacological or surgical) consistently result in reduced exertional dyspnea. The mechanisms by which DH gives rise to exertional dyspnea and exercise intolerance are complex, but recent mechanistic studies suggest that DH-induced inspiratory muscle loading, restriction of tidal volume expansion during exercise, and consequent neuromechanical uncoupling of the respiratory system are key components. This review examines the specific derangements of ventilatory mechanics that occur in COPD during exercise and attempts to provide a mechanistic rationale for the attendant respiratory discomfort and activity limitation.

Relation of Exercise Capacity With Lung Volumes Before and After 6-Minute Walk Test in Subjects With COPD

“…10,12,18,37 Considerable evidence has accumulated that exercise-induced dynamic lung hyperinflation may represent an important factor contributing to exercise intolerance in subjects with COPD. 12,18 Previous studies demonstrated that dynamic hyperinflation can be measured after submaximal exercise such as 6MWT in subjects with COPD.…”

“…10,12,18,37 Considerable evidence has accumulated that exercise-induced dynamic lung hyperinflation may represent an important factor contributing to exercise intolerance in subjects with COPD. 12,18 Previous studies demonstrated that dynamic hyperinflation can be measured after submaximal exercise such as 6MWT in subjects with COPD. 8,11,26 Accordingly, in the present study, dynamic hyperinflation could be observed, as reflected by a significant decrease in inspiratory capacity and inspiratory vital capacity as well as an increase in FRC, RV, and RV%TLC after the 6MWT.…”

“…[4][5][6] Impaired exercise tolerance is a cardinal symptom of COPD, and, although traditionally associated with ventilatory limitations, the mechanisms responsible for the development of exercise intolerance are complex and multifactorial, given the pathophysiological heterogeneity of the disease and the frequent existence of comorbidities. [7][8][9][10][11][12] The distance walked during a 6-min walk test (6MWT) has been shown to be useful for the evaluation of exercise capacity in subjects with COPD. 13,14 Moreover, linear relationships between walking distance and pulmonary function parameters could be demonstrated in several studies.…”

Factors Limiting Exercise Tolerance in Chronic Lung Diseases

“…This disparity leads to intense dyspnea sensation that is the symptom-limiting exercise in a large fraction of patients with chronic lung diseases (155,168). The factors contributing to decreased ventilatory capacity or increased ventilatory requirement/workload are described later in brief.…”

“…1A) (145,212). Combined data from clinical studies (155,180,221) have revealed that the frequency of exerciselimiting symptoms during constant-load exercise in a cohort of 403 patients with moderate to severe COPD was by approximately 60% accountable to intolerable dyspnea sensations, whereas leg discomfort alone or in combination with dyspnea accounted for the remaining approximately 40%.…”