Evaluation of sympathetic vasoconstrictor response following nociceptive stimulation of latent myofascial trigger points in humans.

AIM: Myofascial trigger points (MTrPs) are a major cause of musculoskeletal pain. It has been reported that stimulation of a latent MTrP increases motor activity and facilitates muscle pain via activation of the sympathetic nervous system. However, the magnitude of the sympathetic vasoconstrictor response following stimulation of MTrP has not been studied in healthy volunteers. The aims of this study were to (1) evaluate the magnitude of the vasoconstrictor response following a nociceptive stimulation (intramuscular glutamate) of MTrPs and a breath-hold manoeuvre (activation of sympathetic outflow) and (2) assess whether the vasoconstrictor response can be further modulated by combining a nociceptive stimulation of MTrPs and breath-hold.
METHODS: Fourteen healthy subjects were recruited in this study. This study consisted of four sessions (normal breath group as control, breath-hold group, glutamate MTrP injection group and glutamate MTrP injection + breath-hold group). Skin blood flow and skin temperature in both forearms were measured with laser Doppler flowmetry and infrared thermography, respectively, in each session (before the treatment, during the treatment and after the treatment).
RESULTS: Glutamate injection into MTrPs decreased skin temperature and blood flow in the peripheral area. The magnitudes of the reduction were comparable to those induced by the breath-hold manoeuvre, which has been used to induce sympathetic vasoconstrictor response.
CONCLUSION: The combination of glutamate injection into latent MTrPs together with the breath-hold manoeuvre did not result in further decrease in skin temperature and blood flow, indicating that sympathetic vasoconstrictor activity is fully activated by nociceptive stimulation of MTrPs.