Pathophysiology of exercise intolerance and the role of exercise training in congestive heart failure

Congestive heart failure is the most common discharge diagnosis in patients over 65 years of age. These patients are frequently limited in their daily activities by fatigue, and their 5-year mortality rate is often greater than that of most cancer patients. Developments in the use of vasodilators have reduced mortality and improved symptoms. These advances, however, have been limited, which probably reflects the unclear mechanisms for the progression of heart failure and exercise intolerance. This review examines in detail the pathophysiology of exercise intolerance in congestive heart failure. It seems reasonable to assume that the mechanism for exercise intolerance is the attenuated exercise cardiac output response in congestive heart failure. However, measurements of central hemodynamics have been shown to correlate poorly with systemic exercise performance, suggesting that noncardiac mechanisms limit exercise performance. It has been demonstrated that skeletal muscle function is impaired and may play an independent role in limiting systemic exercise performance. Exercise conditioning improves skeletal muscle function and exercise performance, and reduces the heightened neurohormonal levels that accompany congestive heart failure, a marker for clinical severity and mortality. Major issues that remain to be determined are the mechanism for muscle dysfunction and the role of exercise training, alone or in combination with vasodilators, in reducing symptoms and improving survival.