Attempted handgrip during partial neuromuscular blockade caused significantly smaller increases in muscle sympathetic nerve activity (+56% vs +217%) and mean arterial pressure than actual handgrip.
Does central command (intent to exercise) increase sympathetic discharge to resting skeletal muscle during static exercise in humans?
Central command (the intent to exercise) alone can significantly increase muscle sympathetic nerve activity, arterial pressure, and heart rate, even without actual muscle contraction.
Absolute Event Rate: 56% vs 217%
p-value: p=<0.05
We used intraneural recordings of sympathetic nerve activity in conscious humans to determine if central command increases sympathetic discharge to resting skeletal muscle during static exercise. In nine healthy subjects, we measured arterial pressure, heart rate, and muscle sympathetic nerve activity with microelectrodes in the peroneal nerve of the resting leg during 1) static handgrip at 15% and 30% maximal voluntary contraction and 2) attempted handgrip during partial neuromuscular blockade produced by systemic administration of tubocurarine chloride (0.075 mg/kg i.v.). During curare, subjects reported that they used near-maximal motor effort to attempt a sustained handgrip contraction, but they generated almost no force. Without sustained contraction, the intent to exercise alone, that is, central command, caused statistically significant (p less than 0.05) increases in muscle sympathetic nerve activity as well as in arterial pressure and heart rate. However, the increases in muscle sympathetic nerve activity (+ 56 +/- 16% over control) and in mean arterial pressure (+ 12 +/- 2 mm Hg) during attempted handgrip were much smaller (p less than 0.05) than the sympathetic nerve response (+ 217 +/- 37% over control) and pressor response (+ 25 +/- 3 mm Hg) during an actual static handgrip at 30% maximal voluntary contraction. In contrast, heart rate increased as much during the attempted contraction (+ 18 +/- 2 beats/min) as during the actual contraction at 30% maximal voluntary contraction (+ 16 +/- 4 beats/min). In 11 additional subjects, the heart rate responses during curare were greatly attenuated (p less than 0.05) by atropine but were not significantly affected by propranolol.(ABSTRACT TRUNCATED AT 250 WORDS)
Victor et al. (Tue,) conducted a other in Healthy subjects (n=20). Attempted handgrip during partial neuromuscular blockade (tubocurarine chloride) vs. Actual static handgrip at 30% maximal voluntary contraction was evaluated on Muscle sympathetic nerve activity (p=<0.05). Attempted handgrip during partial neuromuscular blockade caused significantly smaller increases in muscle sympathetic nerve activity (+56% vs +217%) and mean arterial pressure than actual handgrip.