Using the Stimulette Edition 5 with denervated muscles

The Stimulette Edition 5 supports a wide variety of electrotherapy waveforms that are useful for muscle weakness, pain and paralysis. In the case of muscle weakness due to denervated muscles the product supports two classes of waveforms

• “exponential current” - long triangular waveforms that represent a more traditional approach

• “functional electrostimulation” with relatively broad, biphasic, rectangular pulses.

The fundamental problem with denervated muscles is that the nerves cannot be used to trigger a contraction of muscle due to the degradation of both the muscle and neve. Denervated muscles can be made to contract only when stimulated by relatively broad pulses (millisecond rather than the microsecond wide pulses typically seen when using “conventional” FES).

The “exponential current” approach is useful to preserve the muscle bulk but relies on there being a muscle fibre structure still capable of contracting.

In long term denervation both the nerve structure and the contractile structure of the muscle becomes lost over time. The exponential current approach consists of triangular shaped impulses that are 100 to 500 ms wide. When applied to the muscle they will cause a “twitch” type of contraction at a frequency of around 1 Hz. The triangular shaped waveform selectively activates denervated muscle whilst any neighbouring innervated muscles will not respond due to the accommodation ability of the muscle and preserved nerves. This is particularly useful when working with small muscle groups in the shoulder or lower limbs when denervated muscles are close by normally innervated ones.

Application of the exponential current typically starts with the E100 waveform that produces 100 ms impulses. If the degree of denervation is severe the amount of impulse duration will need to be increased. The E200 waveform may be used. In most cases impulse widths of 250 ms are sufficient to produce a muscle contraction. Increasing the current intensity or pulse duration until strong contractions are reached is the normal approach.

The form described as “functional electrostimulation” has been adopted more recently and utilised in research such as the international RISE study that led to the development of the companion product, the Stimulette Den2x. This form uses higher frequencies and a higher number of impulses than the exponential waveform. The pulses are biphasic (positive and negative going) with impulse durations of 60 - 75 ms each with a frequency of approximately 2 Hz. The pulses are delivered in regular “surges”.

The DEN40 waveform is designed to produce 20 Hz tetanic contractions and the DEN120 waveform will produce 2 Hz twitch contractions. In practical applications you would use both but perhaps only see visible contractions with the DEN120 waveform at first. Starting with DEN120 and producing the twitch response encourages a “rebuild” of the contractile mechanism of the muscle over time. It is hard to generalise the exact settings that can be used but certainly the parameters should be fine tuned to suit the individual case. Increasing the current intensity to produce a strong contraction is easily achieved. Typically treatment durations are 5 to 30 minutes but if the muscle contractions cease the treatment is paused and continued after a couple of minutes.

The electrodes used with both waveforms consist of a wet sponge with a conductive carbon electrode. The electrodes should be held in firm contact with the tissues by elastic wraps and cover the muscle as completely as possible without overlapping.

As a guide, it is necessary to use this approach relatively frequently (5 or 6 days per week) at the beginning to restore tissue bulk and quality of muscle structure.

As an example - With a conus caudal lesion requiring stimulation of the quadriceps muscles bilaterally the training plan might be something like this - carried out 5 times per week

First phase 0 to 4 months

DEN120 - 3 or 4 sets of 3 minutes of stimulation with a 1 or 2 minute rest between sets

Second phase 2 to 6 months

DEN120 - 4 or 5 sets of stimulation with 1 or 2 minutes rest between sets

Third Phase 4 to 12 months

DEN40 - 4 to 6 sets of 20 to 40 repetitions with tetanic contraction with 1 minute rest between sets

The Edition 5 can be set into “Home User” mode which only allows one selected waveform type to be used. The User can adjust the stimulation current intensity but otherwise must use the waveform type and parameters established at assessment time.