Abstract
Dyspnea and exercise limitation are among the most common symptoms experienced by patients with various chronic lung diseases and are linked to poor quality of life. Our understanding of the source and nature of perceived respiratory discomfort and exercise intolerance in chronic lung diseases has increased substantially in recent years. These new mechanistic insights are the primary focus of the current review. Cardiopulmonary exercise testing (CPET) provides a unique opportunity to objectively evaluate the ability of the respiratory system to respond to imposed incremental physiological stress. In addition to measuring aerobic capacity and quantifying an individual's cardiac and ventilatory reserves, we have expanded the role of CPET to include evaluation of symptom intensity, together with a simple “non-invasive” assessment of relevant ventilatory control parameters and dynamic respiratory mechanics during standardized incremental tests to tolerance. This review explores the application of the new advances in the clinical evaluation of the pathophysiology of exercise intolerance in chronic obstructive pulmonary disease (COPD), chronic asthma, interstitial lung disease (ILD) and pulmonary arterial hypertension (PAH). We hope to demonstrate how this novel approach to CPET interpretation, which includes a quantification of activity-related dyspnea and evaluation of its underlying mechanisms, enhances our ability to meaningfully intervene to improve quality of life in these pathologically-distinct conditions.
Highlights
Dyspnea and exercise intolerance are commonly the most troublesome symptoms reported by patients with chronic pulmonary diseases and contribute significantly to poor quality of life
This review explores the application of the new advances in the clinical evaluation of the pathophysiology of exercise intolerance in chronic obstructive pulmonary disease (COPD), chronic asthma, interstitial lung disease (ILD) and pulmonary arterial hypertension (PAH)
During the challenge of incremental exercise, the dominant abnormalities in mild COPD include (Figure 2): (1) increased chemostimulation of respiratory centers secondary to the effects of high physiological dead space compared with healthy controls, which is indirectly reflected by higher V E/V Carbon dioxide production (CO2) nadir and steeper V E-V CO2 slope; and (2) increased airways resistance and dynamic hyperinflation (DH) due to the combined effects of peripheral airway disease (EFL), increased ventilatory demand and central motor command output (Ofir et al, 2008a; Chin et al, 2013; Guenette et al, 2014; Elbehairy et al, 2015a,b)
Summary
Dyspnea and exercise intolerance are commonly the most troublesome symptoms reported by patients with chronic pulmonary diseases and contribute significantly to poor quality of life. Cardiopulmonary exercise testing (CPET) alone provides a rigorous evaluation of the interface between respiratory impairment (caused by disease) and reduced exercise capacity in an individual under measured physiological stress It uniquely permits an objective assessment of the integrated functions of the neurosensory, metabolic, respiratory, cardiovascular, and locomotor muscle systems to graded physical exertion. We hope to demonstrate that a simple systematic approach that emphasizes both perceptual and physiological responses (ventilatory control and mechanics) allows the clinician to develop a cogent physiological rationale for effective treatment of dyspnea and exercise tolerance in these common chronic respiratory diseases
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