Effect of increased sympathetic activity on electrical activity from myofascial painful areas.

Abstract

To investigate the effect of increased sympathetic outflow to muscle (by means of elevated intrathoracic pressure) on painful-area electrical activity. In six subjects with myofascial painful areas in trapezius muscles during normal respiration and during elevated intrathoracic pressure, electromyographic epochs were recorded from a monopolar needle electrode inserted over the painful area and advanced until action potentials were detected, a second needle electrode inserted to the same depth over a nontender control area, and surface electrodes placed nearby. The painful-area electromyographic activity increased (P < 0.05) from 49 +/- 53 microV during normal respiration to 121 +/- 80 microV during elevated intrathoracic pressure. The control-area electromyographic activity and the surface-electrode electromyographic activity did not increase significantly. The significant electromyographic increase from painful areas and no significant increase from control channels are consistent with the view that sympathetic neural outflow increases painful-area electrical activity.