BRIEF RAPID COMMUNICATION Skeletal Muscle Metaboreceptor Exercise Responses Are Attenuated in Heart Failure

Background. Resting sympathetic nervous system activity is increased in heart failure. Whether sympathetic nervous system responses during exercise are increased is controversial. Futhermore, the role of muscle metaboreceptors and central command in regulating sympa-thetic outflow has been largely unexplored. Methods and Results. Muscle sympathetic nerve activity (MSNA, peroneal nerve) was measured in nine heart failure subjects and eight age-matched control subjects during static exercise (30%o maximal voluntary contraction) for 2 minutes and during a period of posthand-grip regional circulatory arrest. This maneuver isolates the metaboreceptor contribution to sympathetic nervous system responses. MSNA responses were similar during static exercise in the two groups. During posthandgrip regional circulatory arrest we observed a marked attenuation in MSNA responses in the heart failure subjects (15 % increase in heart failure versus 57 % increase in control subjects). A cold pressor test demonstrated a normal MSNA response to a potent nonspecific stimulus in the heart failure subjects (heart failure subjects, 141 % increase; control subjects, 215 % increase; NS). Nuclear magnetic resonance spectroscopy studies in five separate heart failure subjects and five control subjects suggested that th