ABSTRACT
Respiratory Rehabilitation and Respiratory Division, University Hospitals, and Faculty of Kinesiology
and Rehabilitation Sciences, Katholieke Universiteit Leuven, Leuven, Belgium, and Postdoctoral
Fellow of the Research Foundation-Flanders, Brussels, Belgium
Respiratory Rehabilitation and Respiratory Division, University Hospitals, and Faculty
of Kinesiology and Rehabilitation Sciences, Katholieke Universiteit Leuven, Leuven, Belgium
I. Introduction
Dyspnea, impaired exercise tolerance, and reduced quality of life are common com-
plaints in patients with chronic respiratory disease. Several pieces of evidence point to
the fact that the symptoms associated to chronic obstructive pulmonary disease (COPD)
show only a weak relation to lung function impairment (1). Prediction of exercise
performance based solely on resting pulmonary function tests is inaccurate (2-4). Other
factors, such as peripheral and respiratory muscle weakness and deconditioning are now
recognized as important contributors to reduced exercise tolerance (5-7). Respiratory
muscle weakness contributes to hypercapnia (8), dyspnea (5,9), and nocturnal oxygen
desaturation (10). Signs of inspiratory muscle fatigue during exercise were observed by
several authors (11-13), while debated by others (14). Moreover, inspiratory muscle
strength was significantly correlated to walking distance (6,15). A higher mortality rate
was observed in patients with severe muscle weakness due to steroid-induced myopathy
(16). These are important observations since peripheral and respiratory muscle training
might thus be able to improve physical performance, symptoms, quality of life, and
perhaps, survival in these patients. In many diseases including COPD, interstitial lung
disease, primary pulmonary hypertension, chronic heart failure, and cystic fibrosis,
exercise tolerance showed to be one of the most important predictors of mortality (17-
25). Ergometry is performed to answer the question whether exercise capacity is
impaired, which factors may contribute to the exercise limitation are and to investigate
the safety or risks of exercise (26). Exercise testing is particularly important to quantify
the gains after interventions such as medication, surgical procedures or rehabilitation.
Depending on the specific question, clinicians will rely on more complex tests,
accurately measuring pulmonary gas exchange, cardiocirculatory, andmuscular system,
or may prefer more simple, yet useful tests to answer clinical questions. In the former
case, maximal incremental or constant work rate (endurance) exercise tests may be
required, in the latter, field walking tests may suffice. For some of these tests, however,
the lack of reference values and the absence of physiological measures are important
limitations of the test. Incremental exercise testing and field testing have complementary
value in the assessment of exercise performance (27).
