So long, farewell, Auf wiedersehen, adieu!

Welcome back!  Sadly, we are here writing our last post to you.  We hope this information has been not only educational but practical, something that you can take with you and use in your everyday working lives. Just for you, we have put together a little summary of our journey through our research.

What is denervated muscle?

Denervated muscle is muscle that receives no impulses from the PNS or CNS.  This muscle does not move as transmissions cannot get to the muscle.

What happens to a denervated muscle?

A denervated muscle becomes weak and starts to waste away, this is known as atrophy.  The outcome of an atrophied muscle is a decrease in muscle mass and the size of the muscle fiber.  Myofibrils are seen to decrease and this is replaced with fat and connective tissues.

What are the best types of stimulation for denervated muscles?

 The best type of pulses for denervated muscles is long duration pulses.  Long stimulus duration pulses demonstrated to reduce the amount of fat and connective tissue in denervated muscle.  This kind of pulse produces the longest possible current flow to stimulate muscles into titanic contractions.  There are two types of long duration waveforms: triangular and rectangular.

Triangular waveform is preferred over rectangular because triangular waveforms bypass the nerve and goes directly to stimulate the muscle. This prevents the muscle from accommodating allowing for full excitability and contraction of the muscle.

What are the specific parameters and time length?

Unfortunately there are no set parameters for long stimulus duration pulses. However, as previous mentioned rectangular waveforms are usually 1-600ms and separated by pulse interval of 1ms-several seconds where as, triangular waveforms are 300-1000ms and separated by pulse intervals of ½ to several seconds.  Patients with chronic denervation must keep with electrical stimulation, as once they stop the muscle will atrophy again!  Therefore, patients must spend the time everyday applying estim.

So now, is estim worth it?

The answer to this question is not quite clear cut.  Although estim may not be able to reverse all consequences of long term denervation, there is no denying the positive effects estim has on denervated muscle.  There has been shown an increase in the excitability, in the mass and in myofibril count of denervated muscles.  In patients this can improve cosmetic appearance, provide better cushioning to reduce pressure sores and thus may decrease the time spent in hospital (Salmons et al, 2005).  While these effects themselves maybe worthwhile, the protocol the patient must endure to see these effects is very time consuming.  In one study we found by Valencic et al (1986), improvement in denervated muscles was shown by stimulating the muscle 5 days a week for 20 mins, two times a day for three weeks.  This may not seem too bad but remember for those patients with chronic stimulation, they must keep applying estim or else atrophy will occur again.  More recently, Kern et al (2002), has stated that each muscle group needs to be stimulated for 15-20 mins once or twice a day to induce changes in the muscle, thus if trying to excite more than one muscle group, the patient could be applying estim for 1.5 to 2 hours.

While the benefits of estim are present, it widely depends on the patients goals and motivation on whether or not to take up estim.  For now, estim on permanently denervated muscles would just be for the cosmetic aspects, however with advancing research in medicine, it is possible a reversal of denervation may come to pass.

That is all for Team North America, it has been fun but alas we must say goodbye!

Team North America signing off—

-Megs and Brooke-

References 

Kern, H., Hofer, C., Mödlin, M., Forstner, C., Raschka-Högler, D., Mayr, W., & Stöhr, H. (2002) Denervated muscles in humans: limitations and problems of currently used functional electrical stimulation training protocols. Artif Organs, 26(3):216-8.

Salmons, S., Ashley, Z., Sutherland, H., Russold, M.F., Li, F., & Jarvis, J.C. (2005). Functional electrical stimulation of denervated muscles: basic issues.  Artif Organs, 3:199-202.

Valencic, V., Vodovnik, L., Tefancic, M, & Jelnikar, J. (1986).  Improved motor response due to chronic electrical stimulation of denervated tibialis anterior muscle in humans. Muscle Nerve, 9:612-617.

why was the rectangle jealous of the triangle?

Hello it’s been awhile but we are back again J This time we thought we might share some specifics on the best type of stimulation for denervated muscle as well as how quickly to stimulate.  Just for some background information so you understand the difference once we get into this subject, nerves respond best to quick pulses of less than 1ms in a shorter square shaped waveform. As we told you before, long duration pulses are best muscle for stimulation.

But why is this the best for denervated muscle?

In the simplest terms possible, if the rate of the rise of the current is slow then it won’t provoke a nerve impulse because of the ionic balance across the nerve fiber membrane and is able to adjust itself so the threshold potential rises in response to the applied electric charge, which is known as accommodation (Low et al 1994). The ability to accommodate is much more marked in a nerve than in a muscle because muscle tissue needs a greater electrical charge at a slower spread as it is less excitable than nerves. 

So what pulse is best for this?

Triangular, or accommodation, pulses are most effective for denervated muscle.

There are two types of long duration pulses, accommodation and rectangular. A rectangular pulse is typically 1-600ms separated by pulse interval of 1ms-several seconds.  It is best for stimulation of motor and sensory nerves and denervated muscle.  An accommodation pulse can also be termed as triangular, trapezoidal, sawtooth, senate, slow-rising, shaped, and selective.  They are typically 300-1000ms separated by pulse intervals of ½ to several seconds..

So why is a triangular waveform better than a rectangular waveform if they both work for denervated muscle?

Because of the way that muscles accommodate, when the pulse is long and rectangular, a spike is felt at the beginning of the pulse, and the rest of the time, the muscle builds resistance to the current flowing at a constant voltage (Roberston et al 2006).  However, because a triangular waveform rises so slowly, it bypasses the nerve stimulation level and heads right to the correct stimulation for a muscle, as well as increases the demand on the muscle, rather than leave the stimulation constant, which generates the contraction. The muscle cannot accommodate, or accommodates very slowly, which allows the slow current flow to push the membranes to potential allowing for excitability and contraction of the muscle.

When would I start this stimulation?

Generally, it is best to start soon after the onset of denervation.  This is because the sooner it begins, the less of a chance of atrophy the muscle has.  This is still true even when the nerve might regenerate.  The nerve can take months to regenerate with a muscle, and years to fully heal, so the less atrophied the muscle is, the better chance of regeneration there is.  Just keep in mind the following: When a nerve is severed, both the distal and proximal ends are affected.  However, in some cases, the axon can regenerate, creating sprouts at the axonal tips.  The rate of regeneration is very slow, but studies show that electrical muscle stimulation can reduce or inhibit sprouting (Robinson et al 2008).

Want some more info? J

A study done by Kern et al 2002 showed that biphasic pulses are not necessarily better functionally, but are safer than monophasic pulses.  Monophasic pulses let the ions build up under the skin for hours at a time and can cause burns. So, stick to the biphasic waveforms when doing such a long treatment.

We will leave you to absorb all that. Until Next Time!

Team North America Signing off-

-Megs and Brooke

References:

Bardy, G, Ivey, T., Allen, M., Johnson, G, Mehra, R., Greene, H. (1989) A prospective randomized evaluation of biphasic versus monophasic waveform pulses on defibrillation efficacy in humans. Journal of the American College of Cardiology. 14:728-733.

Low, J., Reed, A. (1994) Electrotherapy Explained: Principles and Practice (2^nd Ed).  China: Elsevier Limited. Great Britain: Clays Ltd.

Roberston, V., Robertson, V., Low, J., Ward, A., Reed, A. (2006) Electrotherapy Explained: Principles and Practice (4^th Ed).  Oxford: Elsevier Limited.

Robinson, A., Snyder-Mackler, L. (2008) Clinical Electrophysiology: Electrotherapy and Electrophysiologic Testing. Maryland:  Lippincott Williams and Wilkins.