Elsevier

Clinics in Chest Medicine

Volume 21, Issue 4, 1 December 2000, Pages 693-704
Clinics in Chest Medicine

Mechanisms and Measures of Exercise Intolerance in Chronic Obstructive Pulmonary Disease

https://doi.org/10.1016/S0272-5231(05)70178-7Get rights and content

Impaired exercise tolerance is a prominent feature of chronic obstructive pulmonary disease (COPD).46, 59 Patients with COPD demonstrate widely variable exercise capacities, however, even when judged to have identical degrees of impairment by standard pulmonary function tests.77 This variance probably reflects the complex pathogenesis of exercise intolerance, which includes a large number of variables ranging from processes in the central nervous system to peripheral muscles:

  • Reduced expiratory airflow caused by poor elastic recoil

  • Increased airways resistance leading to increased work of breathing and increased ventilatory drive

  • Reduced pulmonary vascular bed and increased pulmonary vascular resistance

  • Impaired cardiac output because of factors that impede right heart filling and factors that impair left ventricular systolic function

  • Muscle dysfunction

  • Nutritional status and body composition

In addition, the term COPD does not describe one homogenous disease process but, rather, a heterogeneous group of disease subtypes that share airway obstruction as a prominent feature.

The symptoms that limit the exercise performance of the patient with COPD typically include exertional dyspnea, fatigue, muscle weakness and leg discomfort.50 Dyspnea is thought traditionally to reflect the many processes that cause ventilatory limitation.52, 60 The symptom of muscle weakness and discomfort likely reflects the sense of peripheral muscle effort.20, 35 Cardiovascular factors, and in some cases, psychologic issues may play a role in the fatigue that many patients with COPD describe with exercise.13, 15, 90

All of these symptoms occur with exercise to some degree, and dyspnea is usually a predominant symptom. Recently, however, leg fatigue attributable to peripheral muscle weakness has also been recognized as a common limiting symptom during exercise.53

Standard pulmonary function testing provides information on functional lung capacity at rest but provides limited information on ventilatory requirements or functional performance during exercise. It is important to examine the pathophysiologic changes during exercise in this patient population in order to understand the basis for exercise intolerance in COPD. A thorough understanding of the basis of exercise intolerance can, in turn, assist in identifying the optimal spectrum of treatment interventions for individual patients.

Section snippets

VENTILATORY LIMITATION DURING EXERCISE

A number of processes that affect ventilation interact in the patient with COPD to reduce exercise tolerance and increase breathlessness. Reduced exercise tolerance results from increased ventilatory requirements and reduced ventilatory capacity. Airflow limitation, a hallmark feature of COPD, leads to altered ventilation-perfusion (V/Q) matching in the lung. Loss of elastic recoil also occurs in patients with emphysema. As a result of V/Q mismatching, physiologic deadspace and the ratio of

RESPIRATORY MUSCLE FUNCTION DURING EXERCISE

Although traditionally the most widely accepted explanation for exercise limitation in COPD is decreased ventilatory capacity because of diseased airways and lung-parenchyma, recent attention has also focused on respiratory muscle function. Respiratory muscle strength appears to be an important determinant of exercise tolerance in patients with COPD.4, 58 Data from normal volunteers indicate that the perception of dyspnea during exercise correlates best with the degree of respiratory muscle

CARDIAC LIMITATION DURING EXERCISE

Pathologic studies support the concept that right ventricular hypertrophy and dilatation frequently accompany COPD.85 The role of the cardiovascular system as a cause of exercise limitation in COPD, however, has been thought traditionally to be minimal.13, 22 This view was based on the belief that patients with COPD could not exercise intensely enough to achieve cardiac limitation. Recent work has suggested, however, that the profound respiratory mechanical changes seen in patients with severe

PERIPHERAL MUSCLE WEAKNESS

There is a growing body of evidence supporting a role for peripheral muscle dysfunction as a significant contributing factor to exercise intolerance in patients with COPD.19, 30, 34 This topic is reviewed extensively in the article by Maltais and colleagues elsewhere in this issue. In brief, leg fatigue and discomfort can be the main limiting symptoms during exercise in up to 40% of patients with COPD.34, 53 Peripheral muscle abnormalities in COPD that have been described include reductions in

NUTRITIONAL STATUS AND EXERCISE LIMITATION

Malnutrition, as defined by body weight less than 90% of ideal body weight, has been reported in up to 25% of patients with COPD.91, 92 The importance of this finding is reflected in the well-known increase in mortality rate among malnourished patients with COPD.11 Malnutrition has been demonstrated to affect ventilatory and peripheral muscle strength adversely, thereby reducing exercise tolerance.1 The causes of malnutrition in COPD are not well understood but may include a hypermetabolic

PSYCHOLOGIC VARIABLES IN CHRONIC OBSTRUCTIVE PULMONARY DISEASE

Approximately 45% of patients with COPD describe restrictions in their daily activities, yet physiologic variables may only explain a portion of this disability.68, 79 Psychologic factors such as depression, outlook, and level of self-esteem may also play a role in functional impairment.27 Weaver et al90 evaluated the relationship between physiologic and psychologic variables and functional status in COPD. They examined 104 patients with COPD and measured functional status (Pulmonary Functional

MEASURES OF EXERCISE INTOLERANCE IN CHRONIC OBSTRUCTIVE PULMONARY DISEASE

It is often necessary to quantitate the degree of exercise intolerance experienced by the patient with COPD. Measurement of exercise tolerance can assist in diagnosis of symptoms, enable the assessment of the functional impact of disease progression over time, and identify responses to treatment interventions, such as pulmonary rehabilitation or medication. Exercise tolerance can be assessed by several methods. The choice of method in individual patients depends on equipment availability,

SUMMARY

The mechanisms for exercise intolerance in chronic obstructive pulmonary disease are complex and multifaceted. Although ventilatory limitation caused by abnormal pulmonary function is a major contributor to this phenomenon, other factors may play an important role in limiting exercise. These other factors include depressed cardiac function, respiratory and peripheral muscle weakness, nutritional imbalances, and psychologic factors. The assessment of the pulmonary patient who complains of

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    Address reprint requests to Linda Nici, MD, Division of Pulmonary and Critical Care Medicine, Department of Medicine, Rhode Island Hospital, 593 Eddy Street, Aldrich Building 124, Providence, RI 02903, e-mail: [email protected]

    *

    Division of Pulmonary and Critical Care Medicine, Department of Medicine, Rhode Island Hospital and Brown University, Providence, Rhode Island

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