Anything physiological has to do with the body and its systems. You might notice that your physiological response to a scary movie includes your heart beating faster and your hands getting sweaty.
You know that the root word of physiological is phys, which refers to the body (think of those phys. ed. classes you panted through). That root comes from the Greek word for nature. Add the suffix ology, which means “the study of” (see where we’re going?), and finally, tack on that little ical. Ta-taa! You have turned the root into an adjective to describe the way your body works. Let’s get physiological!
The physiological basis for DN depends upon the targeted tissue and treatment objectives.
The treatment of myofascial trigger points (referred to as TrPs) has a different physiological basis than treatment of excessive muscle tension, scar tissue, fascia, and connective tissues. TrPs are hyperirritable spots within a taut band of contractured skeletal muscle fibers that produce local and/or referred pain when stimulated. TrPs are divided into active and latent TrPs dependent upon the degree of irritability.
Active TrPs are spontaneously painful, while latent TrPs are only painful when stimulated, for example, with digital pressure. TrPs can be visualized by magnetic resonance imaging and sonography elastography, Which has shown that active TrPs are larger than latent TrPs and feature a reduction in circulation.
TrPs are physiological contractures, characterized by local ischemia and hypoxia, a significantly lowered pH (active TRPs only), a chemically altered milieu (active TRPs only), local and referred pain, and altered muscle activation patterns.
Although latent TrPs are not spontaneously painful, recent research has shown that they do contribute to nociception, therefore they need to be included in the treatment plan. TrPs are associated with dysfunctional motor endplates, endplate noise, and an increased release of acetylcholine. TrPs activate muscle nociceptors and are peripheral sources of persistent nociceptive input, thus contributing to the development of peripheral and central sensitization.
Stimulation of TrPs activates the periaqueductal grey and anterior cingular cortex in the brain, and enkaphalinergic, serotonergic, and noradrenergic inhibitory systems associated with A-δ (A delta) fibers through segmental inhibition. DN can be divided into deep and superficial DN.
Deep DN has been shown to inactivate TrPs , which are modulated by the central nervous system. DN has been shown to be associated with alleviation and mitigation of spontaneous electrical activity or motor endplate noise ;a reduction of the concentration of numerous nociceptive, inflammatory, and immune system related chemicals; and relaxation of the taut band. Deep DN of TrPs is associated with reduced local and referred pain, improved range of motion, and decreased TrP irritability both locally and more remotely. DN normalizes the chemical milieu and pH of skeletal muscle and restores the local circulation.
Superficial DN is thought to activate mechanoreceptors coupled to slow conducting unmyelinated C fiber afferents, and indirectly, stimulate the anterior cingular cortex. Superficial DN may also be mediated through stimulation of A-δ fibers, or via stretching of fibroblasts in connective tissue. Superficial DN is associated with reduced local and referred pain and improved range of motion, but it is not known at this time whether superficial DN has any impact on normalizing the chemical environment of active TrPs or reducing motor endplate noise associated with TrPs in general.
The physiological basis for DN treatment of excessive muscle tension, scar tissue, fascia, and connective tissues is not as well described in the literature, but the available research shows that there may be several benefits. Muscle tension is determined by a combination of the basic viscoelastic properties of a muscle and its surrounding fascia, and the degree of activation of the contractile apparatus of the muscle. There is some evidence that excessive muscle tension, as seen for example in spasticity, can be alleviated with DN.
Scar tissue has been linked to myofascial pain and fibroblasts. Fibroblasts are specialized contractile cells within the fascia that are of particular interest, as they synthesize, organize, and remodel collagen, dependent upon the tension between the extracellular matrix and the cell. DN, especially when used in combination with rotation of the needle, can place fibroblasts in a high tension matrix, at which point the fibroblast changes shape and assumes a lamellar shape, and increases its collagen synthesis and cell proliferation. DN has been shown to directly activate fibroblasts through mechanical manipulation of the needle, which in turn activates the release of cytokines and other pro-inflammatory mediators. DN can play a substantial role in the process of mechanotransduction, which is described as the process by which the body converts mechanical loading into cellular responses. Fibroblast activation with a solid filament has been shown to result in pain neuromodulation.