Neuromuscular diseases as models of cardiovascular regulation during exercise.

This article reviews the research performed to date on the cardiovascular responses to exercise in patients with neuromuscular diseases and lesions affecting the transmission of afferent impulses from skeletal muscle. These studies have provided important information about the roles of central command and reflexes from skeletal muscle afferents in circulatory control. Few animal models of neuromuscular diseases are available. Studies of patients with specific defects in skeletal muscle energy metabolism are particularly valuable because the local metabolic state participates in both systemic and local cardiovascular regulation. In patients with certain muscle metabolic defects (e.g., McArdle's disease, carnitine deficiency) cardiac output is normal at rest but increases excessively in relation to oxygen uptake during exercise. The excessive increase in cardiac output during exercise can be totally or partially normalized by increasing the availability of substrate to exercising muscle. These studies provide unique insights into the specific metabolic factors which are involved in cardiovascular regulation.