Low and medium Frequency Electrotherapy - Implox

2 PAIN CONTROL AND SELECTIVE STIMULATION
2.1 Introduction
Pain reduction can be achieved in many different ways. It is beyond the scope of this book to list all the means
available. However, we shall discuss a number of the theories that have been advanced to explain the underlying
mechanism of the pain reduction effect. With respect to electrotherapy, it will become clear that phase duration,
frequency and amplitude play an important role.
2.2 Pain theories
Enraf-Nonius electrotherapy equipment offers a range of current types that relate to the present-day theories
explaining the reduction of pain by electrostimulation. The following three theories are important.
2.2.1 Gate control theory (Melzack and Wall)
This theory (7.21) is based on the assumption that stimulation of the thick myelinated nerve fibres will cause a neural
inhibition at the spinal level. This inhibition will block the transport of pain stimuli to the brain via the thin nonmyelinated
nerve fibres.
Type II and III
nerve fibres
+
Central Control
+
Action
system
Substantia
Gelatinosa
-
Type IV
nerve fibres - +
GATE CONTROL SYSTEM
-
Transmision
cell
(Lamina
V)
Fig. 1.
Diagrammatic representation of the Gate-Control-Theory (Melzack and Wall).
In other words, selective stimulation of the type II and type III nerve fibres will create a feed-forward inhibition of the
stimuli arising in the type IV nerve fibres. In this case, stimulation of the type IV nerve fibres is undesirable.
Although the existence of a central influence is now also considered (see paragraph 2.2.2), the Gate control theory is
still regarded as one of the most important starting points in pain suppression (7) .
Category Efferent Afferent Conductionspeed (m/s) Diameter
(µm)
A-a I 70-120 12-22
Thick A-ß II 50-70 5-12
A-? II 30-50 5-12
A-d III