Effect of nerve block on sural amplitude during remote muscle contraction.

We previously reported that the median sensory nerve action potentials (SNAPs) increased in amplitude during both near (3) and remote (4) muscle contraction. The objective of the present project was to begin to study the pathway by which this occurred. The sural amplitude was measured after one min. of isometric biceps contraction and compared pre and post lidocaine nerve block in 10 healthy subjects. The baseline was defined as the least amount of current needed to elicit a minimal sural response pre contraction. This level of stimulus remained constant throughout the experiment. Results showed that the sural amplitude peaked 4 min. after muscle contraction. An 8.1 microV increase in sural amplitude from baseline was noted pre injection as 5 min. post contraction, and an increase of 13.4 microV was noted comparing pre to post injection amplitudes at the same time. Statistical analysis using two-way interaction comparing the time courses pre and post injection showed a 92% chance the responses were dissimilar Post hoc least significant difference (LSD) analyses were significant at 4 min. (p = .005) and 6 min. (p = 0.29) post contraction. In conclusion, the increase in sural amplitude after remote muscle contraction was no longer apparent after proximal sural nerve block. This suggests that the nerve itself is required in the final common pathway for the transmission of this induced signal.