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.

It doesn't matter! It's in the past!

Hello again!

Just came across something very interesting and decided to write a quick update on our previous blog. 

We found a newer study done by Ashley et al (2008) that is sure to keep past researchers on their toes. The study used 5 different stimulation patterns with a range of parameters on chronically denervated muscles of a rabbit (patterns shown in table below).  This study was interesting b/c they did use subcutaneous electrodes, which can stimulate without as much resistance from connective tissue or fat.

We know you are thinking.. So what does that table mean?

All of these diverse parameters were shown to restore muscle fiber size and function with little to no difference between the different patterns. This study does support rectangular pulsed currents, but also shows that even varying parameters can regenerate the muscle to a certain amount.  We think this can be helpful because it means that a person who has a busy daily life might be more compliant if they don’t have to take as much time or spend multiple times a day on estim, and can still get the same result. 

So it sounds like a lot of work.. how many months/years does the patient need to stimulate for?

Another good point that we thought Ashley et al made is that the patient has to keep with it. If they stop the stimulation, the muscle will atrophy again! The time spent doing this can be worth it, due to the fact that it can keep them out of the hospital more, as well as improve daily activities and overall health, but it also depends on the patient and how willing they are to keep with it.

Sounds eccentric and dangerous..  Is this safe?

This study was also very useful to demonstrate that no matter how long or how often, the stimulation is safe.  While no parameters have been found in previous research that have been limiting, the extent that the 4^th pattern goes to helps to show how safe the stimulation is.

We know, this is contradictory, we told you one thing and now we are thinking another, but that’s the way the cookie crumbles with this topic!  Keep in mind though that this study was done with subcutaneous electrodes, so we don't know if these principles apply to surface electrodes as well. Further research tells us the important parameters of estim are not agreed upon among practitioners (Eberstein & Eberstein, 1996).  It is quite controversial what is correct and most effective, so we thought we would give you all the info and let you chew on it for awhile.  We will be back with more stimulation for you very soon. Until next time! J

Team North America Signing off-

-Megs and Brooke

Reference

Ashley, Z., Sutherland, H., Russold, M.F., Lanmüller, H., Mayr, W., Jarvis, J.C., & Salmons, S. (2008). Therapeutic stimulation of denervated muscles: the influence of pattern. Muscle Nerve. 38(1):875-68

Need help finding your pulse?

Hello again! We are back to talk more about estim and its effects on muscle denervation.  Last time we discussed what a denervated muscle was, today, you are in for a real treat as we discuss what the best type of stimulation for denervated muscles is!

Not all stimulation patterns are equally effective in treating denervated muscles (Eberstein &Eberstein).  To be effective, estim must stimulate all denervated muscle fibers!  This would be very time consuming and somewhat near impossible without the use of implanted electrodes (Eberstein & Eberstein, 1996).  For example, with 2 independent stimulation channels, electrodes are placed in the glutes, quadriceps, hamstrings, and triceps surae. Each of the muscle groups would need to be stimulated for 15-20 mins once or twice a day resulting in up to 2 hours of stimulation a day!


So now, Q: how do we overcome this issue? 


A: long stimulus duration pulses (Eberstein & Eberstein, 1996).  In an interesting study performed by Mokrusch I et al, (1990), chronically denervated rabbit muscle was stimulated twice a day  for 6 minutes by bidirectional long rectangular impulse of constant current to the point where muscle contractions were isometric, titanic and strong.  The results produced a muscle with decreased fat and connective tissue, both, as you learned earlier, are found in chronically denervated muscle.  Mokrusch et al (1990) believes that when using surface electrodes to produce a strong tetanic contraction on denervated muscle, that rectangular impulses were most effective because they encourage the longest possible current flow. Herbison et al (1971) did a study that supported this idea.  A low impulse square wave on rat denervated muscle found no significant effect on the muscle, but, when long impulses were used, there was a significant increase in muscle weight.


On reflection of what we have read, we think that the results of these studies suggest that the best electrical stimulation to use for denervated muscles is a long pulse duration current.  A few facts that lead us in this direction are that long pulse duration current works the best with surface electrodes and high frequency, which is needed to stimulate the denervated muscle fibers into titanic contraction. 


So the question now is ‘what are the benefits of electrical stimulation and how do we keep it safe to use?’- Stay Tuned, Until next time!
Team North America signing off--

-Megs and Brooke

References:

Mokrusch, T., Engelhardt, A., Eichhorn, F., Prischenk, G., Prischenk, H., Sack,  G., & Neundörfer, B. (1990). Effects of long-impulse electrical stimulation on atrophy and fibre type composition of chronically denervated fast rabbit muscle. Neurol. 237: 29-34

Eberstein, A. & Eberstein, S. (1996). Electrical stimulation of denervated muscle: is it worthwhile?. Med Sci Sports Exerc. 28(2)1463-1469.

Kern, H., Hofer, C., Modlin, M., Forstner, C., Raschka-Hogler, D., Mayr, W. & Stohr, H. (2002). Denervated Muscles in Humans: Limitations and Problems of Currently Used Functional Electrical Stimulation Training Protocols. Artifical Organs. 26(3): 216-218

Herbison, G.J., Teng, C.S., Reyes, T., & Reyes, O. (1971). Effect of electrical stimulation on denervated muscle of rat. Arch Phys Med Rehabil. 52 : 516-522

You've Got a lot of Nerve!! or maybe not...

Hello! And welcome to our blog. As physio students delving into the use of estim in different modalities, we have created this blog to answer this one question: Does estim affect denervated muscle?

Ok so you are probably wondering what that even means?  What is denervated muscle?

Denervated muscle is muscle that is completely separated from nerve fibers, meaning it is getting no impulses from the Central Nervous System (CNS) or Peripheral Nervous System (PNS). Basically that means that the transmission of the impulses telling the muscles to contract or relax are not getting through most of the time or sometimes even at all, and the muscle is affected chronically, or long-term. 

So what happens to a muscle when it is denervated?

The most common finding is that denervated muscle begins to atrophy. Depending on the size and location of injury and how long the muscle has been denervated, it may have atrophied completely, causing more difficulties with electrical stimulation.

An article we found very interesting by Goldspink et al, in a study done on rats, found that the weight of the muscle may drop by 50% after a month, which also associates with a loss in the diameter of the muscle fiber by more than 50%. Two things that are important to remember about this change though are that this study is done on rats. Equal loss in size in humans probably takes a month or two longer, and even can be variable from muscle to muscle. Also, the fibers still are regular with the same striations as at their full weight, but they do have a decreased numbers of myofibrils.  After a year or so, the number of myofibrils is significantly reduced, and fat and connective tissue has filled much of what used to be muscle, which we think is significant because it will have less of a reaction to a surface electrode.  The results of Goldspink’s study show that atrophy of denervated muscle seems to be due to the change in the activity pattern of the muscle, rather than just the lack of nerve supply for protein synthesis. Opposite to our first thoughts, we think this is important to note as we get more into how electric stimulation works because it means that there might be hope for the activity that the stimulation could put on the muscle. However, much of this depends on how long the muscle has been denervated for.

For visual stimulation, here is an example of the different amounts of myofibrils, connective tissue, adipocytes and collagen over time as the denervation takes place.

picture obtained from http://www.rehab.research.va.gov/jour/05/42/3suppl1/kern.html

So the question is, does estim help with contraction, activation, or rebuilding of this chronically atrophied denervated muscle?  As for what we have read so far, estim, over long periods of time, does have benefits. The studies we have looked at so far have all been done on rats or rabbits, and all point to increases in certain elements but not full recovery. But for now, we will let you wrap your head around that as we gather more research.  In future posts we will get detailed on what type of stimulation is best, how to keep it safe, whether or not it can improve or prevent muscle atrophy, and whether or not the benefits outweigh the risks.  Until next time!!
Team North America signing off -


-Megs and Brooke-


Reference:
Goldspink, G., Tabary, C. Tabary, J.C., Tardieu, C., Tardieu, G. (1973). Effect of Denervation on the Adaptation of Sarcomere Number and Muscle Extensibility to the Functional Length of the Muscle: Journal of Physiology. 236, 733-42.