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.