The ability to perform daily activities is an important component of an individual's quality of life. A common clinical presentation is a change in a patient's ability to perform daily activities, often because of increasing fatigue or shortness of breath. Many conditions can contribute to these complaints, including, in addition to heart and lung disease or their combination, obesity, hypertension, or peripheral vascular disease. These complaints are often addressed by the clinician using information readily available at rest. However, since the patient's symptoms occur during exercise, it is advantageous to investigate their cause during exercise under controlled conditions. In addition, although common clinical tests such as resting pulmonary function or a nuclear study of resting ventricular function can help diagnose the presence of lung and heart disease, they tend to be poorly related to exercise tolerance. Thus, an exercise test, including the measurement of ventilation and gas exchange responses, can be of particular value in distinguishing the cause of an individual's exercise limitation. Exercise testing with ventilatory gas exchange analysis (or “cardiopulmonary” exercise testing) has gained popularity both due to the recognition of its value in the functional assessment of patients with cardiovascular or pulmonary disease, and due to the fact that technological advances have made this modality easier to use.

Cardiopulmonary exercise testing has also become more widely applied because it substantially increases the yield of information related to cardiopulmonary function. This information has applications not only for helping to establish the cause of exercise intolerance, but also for prognosis, determination of disability, and making judgements concerning therapeutic interventions. Peak o₂ is now widely recognized as an important factor in the risk paradigm among patients with cardiovascular disease. During the 1990s, at least 50 studies were published demonstrating that peak o₂ is a univariate or multivariate predictor of outcomes in patients with chronic heart failure (CHF). This article addresses the clinical applications of exercise testing with gas exchange analysis, beginning with a review of the cardiopulmonary response to exercise and how this response is disturbed by cardiovascular or pulmonary disease. This is followed by an overview of clinical applications of cardiopulmonary exercise testing.