HAND GRIP EXERCISE AS A MEASURE OF SYMPATHETIC NERVE ACTIVITY

In normal subjects, skin sympathetic nerve activity is thought to be an index of central command. Central command is the central activitation of the sympathetic nervous system along with recruitment of alpha motor neurons in initiating muscular activity. When normal subjects exercise, skin sympathetic nerve activity rises promptly and is sustained throughout the static handgrip. During a period of post handgrip circulatory arrest, a maneuver which isolates the effects of metabolite sensitive afferents in the exercising muscle, skin sympathetic nerve activity falls to baseline levels. Congestive heart failure subjects fatigue earlier and generate a greater level of metabolites when performing a similar level of activity. In congestive heart failure, elevated skin sympathetic nerve activity is maintained during post handgrip circulatory arrest. In order to differentiate whether this altered pattern of skin sympathetic nerve activity is due to greater metabolite generation or to an abnormality in sympathetic regulation in congestive heart failure, we will perform progressive static handgrip. Each subject will perform three bouts of static handgrip to fatigue followed by post handgrip circulatory arrest. Subjects will do progressively harder workloads of 35, 45 and 60% maximum voluntary contraction. Each bout will be followed by a rest period.