Abstract
Compression at myofascial trigger points (MTrPs), known as “ischemic compression,” has been reported to provide immediate relief of musculoskeletal pain and reduce the sympathetic activity that exacerbates chronic pain. We conducted a pilot study to investigate the possible involvement of the prefrontal cortex in pain relief obtained by MTrP compression in the present study, and analyzed the relationships among prefrontal hemodynamic activity, activity of the autonomic nervous system, and subjective pain in patients with chronic neck pain, with and without MTrP compression. Twenty-one female subjects with chronic neck pain were randomly assigned to two groups: MTrP compression (n = 11) or Non-MTrP compression (n = 10). Compression for 30 s was conducted 4 times. During the experiment, prefrontal hemodynamic activity [changes in Oxy-hemoglobin (Hb), Deoxy-Hb, and Total-Hb concentrations] and autonomic activity based on heart rate variability (HRV) were monitored by using near infrared spectroscopy (NIRS) and electrocardiography (ECG), respectively. The results indicated that MTrP compression significantly reduced subjective pain compared with Non-MTrP compression. The spectral frequency-domain analyses of HRV indicated that a low frequency (LF) component of HRV was decreased, and a high frequency (HF) component of HRV was increased during MTrP compression, while LF/HF ratio was decreased during MTrP compression. In addition, prefrontal hemodynamic activity was significantly decreased during MTrP compression compared with Non-MTrP compression. Furthermore, changes in autonomic activity were significantly correlated with changes in subjective pain and prefrontal hemodynamic activity. Along with previous studies indicating a role for sympathetic activity in the exacerbation of chronic pain, the present results suggest that MTrP compression in the neck region alters the activity of the autonomic nervous system via the prefrontal cortex to reduce subjective pain.
Highlights
The prevalence of neck pain in the general population has been increasing in recent years (Hoy et al, 2010), and women complain more frequently of neck pain than men (Guez et al, 2002; Côté et al, 2004; Fejer et al, 2006)
We conducted a pilot study to investigate the effects of compression at myofascial trigger points (MTrPs) in the neck region of patients with chronic neck pain on subjective pain perception, prefrontal hemodynamic activity, and possible autonomic activity using near infrared spectroscopy (NIRS) and heart rate variability (HRV) analyses
HRV parameters that are believed to reflect parasympathetic activity were significantly increased during compression at MTrPs compared with that induced by compression at Non-MTrP, and HRV parameters that are believed to reflect sympathetic activity were decreased
Summary
The prevalence of neck pain in the general population has been increasing in recent years (Hoy et al, 2010), and women complain more frequently of neck pain than men (Guez et al, 2002; Côté et al, 2004; Fejer et al, 2006). MTrPs are hypersensitive spots in palpable taut bands of skeletal muscle fibers (Simons et al, 1999), and recent clinical studies have reported that patients with chronic neck pain have a larger number of MTrPs in the upper trapezius muscle than healthy subjects (Fernández-de-las-Peñas et al, 2007; Muñoz-Muñoz et al, 2012). These studies suggest that MTrPs are responsible for chronic neck pain.
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