Low and medium Frequency Electrotherapy - Implox

The Amplitude Modulation Frequency (AMF) has no effect on the selective stimulation of thick nerve fibres, but only
determines the frequency with which the nerve fibres depolarize.
Different AMF’s produce different sensations in the patient, enabling the current to be adapted to the sensitivity of the
affected tissues. The choice of AMF is therefore of therapeutic significance.
2.3.3 Wyss
Wyss (18,35) investigated the selectivity f using direct current pulses of different phase times for A and B fibres (Fig. 5).
It appeared that A fibres were selectively stimulated by shorter pulses with lower amplitude than those required for
selective stimulation of B fibres. Although no definitive physiological explanation has yet been given for the effects of
the 2-5 current and the diadynamic current forms, it is striking that the phase duration of these currents corresponds
closely with that reported by Wyss as being the optimum for the stimulation of thick nerve fibres, even though Wyss
used exponential pulses. The phase duration of the (neo)faradic current forms appears to fit this model extremely
well.
Fig. 5.
The dependence of the threshold voltage on different rise times (for A and B fibres) with progressively increasing
pulses, according to Wyss.
2.4 Amplitude (stimulation level)
From the investigations mentioned above it is clear that, in addition to phase duration and frequency, the amplitude is
also a determining factor in selective stimulation (Fig. 3, 4 and 5). In electrostimulation, reference is made to various
stimulation levels, in order to indicate how high the amplitude should be in order to achieve truly selective stimulation.
When the amplitude in a healthy subject is increased, the following reactions occur:
a. the sensitivity threshold is reached;
b. the motor threshold is reached;
c. the pain threshold is reached; the patient experiences contractions and pain (Fig. 6).
This applies to all current types! It is therefore essential to check the patient’s sensitivity before treatment.
C
B
A
B
C
A
A
B
C
sensitivity threshold
motor threshold
pain threshold
10
Fig. 6.
Coherence of stimulation level and amplitude.