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January2010 Vol.47 Issue:      1 Table of Contents
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Effect of Low Pulsed Magnetic Field Therapy on The Motor Neuron Excitability in Normal Subjects

Awatef M. Labib1, Samy Abdel Hamid1, Hanan Hosny2

 

Departments of Physical Medicine, Cairo University1,

Clinical Neurophysiology, Bani Swoeif University2; Egypt

 



ABSTRACT

Background: Pulsed magnetic field therapy has the ability to modulate neuropathic pain. Objective: The aim of our work is to investigate the effect of the low pulsed magnetic field therapy (LPMFT) on the motor neuron excitability in normal subjects Methods: Thirty volunteer male subjects were studied; assigned randomly into two groups; a study group (20 subjects) and a control group (10 subjects). The study group received LPMFT with a frequency of 10Hz and an intensity of 60 G for 30 min at the posterior aspect of the right calf muscle. The H reflex latency, amplitude, H/M ratio and intensity threshold were measured within 30 minutes before and after application of the therapy and 30 minutes after.  Results: A statistically significant decrease in H intensity threshold in the study group was noticed (P< 0. 0001). Conclusion:  Low pulsed magnetic field with a frequency of 10 Hz and an intensity of 60 G can increase the motor neuron excitability, providing us with an effective modality that could be used for the treatment of many neurological disorders. (Egypt J Neurol Psychiat Neurosurg. 2010; 47(1): 131-136)

 

Key Words: LPMF, motor neuron excitability, pain.             

Correspondence to Hanan Hosny, Department of clinical neurophysiology, Bani Sueif University, Egypt. Tel: +020101464397  E-mail:hosny_hanan@hotmail.com.





INTRODUCTION

 

                Transcranial electrical and electromagnetic stimulation methods of the human brain are now widely used in research and in clinical practice to evoke motor responses1. It had been proved to be an effective tool to modify the excitability of the cerebral cortex and affect spinal segmental excitability by changing the descending cortico-spinal projections2,3.

The theory behind the use of magnetic fields to increase the blood flow stems from a physics principle known as the "hall effect". It implies that an electromotive force can cause charged particles to accumulate towards each other like poles creating a magnetic field. This magnetic field induces a voltage against concentration gradient and is known as the Hall voltage. The movement of these particles is resisted because the particles are forced to accumulate against their normal direction of flow. This migration against resistance may cause production of heat that in turn would result in blood vessel dilation. Because substantial evidence exists that pulsed electromagnetic fields (PEMF) safely induce small electrical eddy currents within the body that can depolarize, repolarize and hyperpolarize neurons, it was hypothesized that these electrical currents could potentially influence neuropathic pain scores.

It was also postulated that this energy can inhibit transmission of the action potentials or block the   propagation of nerve impulses so they can prevent sensory conduction.4 Magnetic field (MF) is in principle, capable of inducing selective changes in the microenvironment around and within the cell, as well as the cell membrane, and it might be a practical method for inducing modifications in the cellular activity.

Any change in the electrochemical microenvironment of the cell can cause modifications in the structure of its electrified surface regions by changing the concentration of a specifically bound ion or dipole that may be accompanied by alterations in the conformation of molecular entities (such as lipids, proteins, and enzymes) in the membrane structure. Therefore, even small alterations in transmembrane voltage could trigger a significant modulation of the cell function.5

 

The H-reflex is a valuable tool to evaluate the neurologic function in various populations. It is an estimate of the alpha motor neuron excitability when presynaptic inhibition and intrinsic excitability of the motorneuron remain constant.6 The H reflex amplitude provides an indication of the number of nerve fibers activated by electrical stimulation7, while The H reflex latency is the time interval between the onset of a stimulus and the onset of a response8. In addition, the H reflex intensity threshold is the stimulation strength sufficient to evoke a maximum response size.7

The aim of this study is to evaluate the effect of LPMF on the spinal motor neuronal excitability as measured by the H-reflex parameters.

 

SUBJECTS AND METHODS

 

Subjects:

     This study included thirty male volunteers, ages ranged from 18 to 27 years old with a mean age of (21.66±1.87) years, height ranged from 160 to 185 cm with a mean value of (174.53±6.74) cm and weight ranged from 55 to 98 kg with a mean value of (70.525±11.32) kg. All should have no history of neurological, orthopedic, urinary, cardiovascular or psychological problems that may affect the motor neuron excitability, be non-smokers, avoid heavy physical activities 12 hours before the study, refrain from drinking or eating any substance containing caffeine, with no history of taking any tranquillizers or analgesics that may influence the motor neuron excitability. They were randomly assigned into two groups; study and control groups; Study group: included 20 normal subjects received (LPMFT) with a frequency of 10 Hz and an intensity magnitude of 60 G for 30 minutes. It was applied on the posterior aspect of the right leg. The H-reflex amplitude, H/M ratio, H-reflex latency, and H-reflex intensity threshold were measured 3 times; before, immediately after application and after 30 minutes of application. Control group: included 10 normal subjects used as a guide for variations of the H reflex excitability, they were examined for H-reflex amplitude, H/M ratio, H- reflex latency, and H-reflex intensity threshold measured twice within 30 minutes.

 

Methods: 

I.       Computerized four channel EMG Tonnies neuroscreen plus 1,59 was used to record the H-reflex amplitude, latency and H/M ratio.  The H-reflex was elicited by stimulation of the posterior tibial nerve at the popliteal fossa using 1.0 ms pulse duration; square wave was applied with a stimulus frequency one every 2 sec, and a wide range of stimulus intensities were applied starting from that needed to obtain the threshold value of the H or the M  to the highest value required for a maximum M value (M max). This range of stimulus intensity also provided the maximum value of the H reflex (H maximum); the normalized value of H max/M max was computed for each subject. Measurement of the H-reflex latency was carried from the stimulus onset to the first deflection from the baseline.

II.     Low Pulsed Magnetic Field  Therapy: MTS 20 manufactured by VIDA ELETIRONICA according to the standards of national and international safety (CEI65-CEI 62.24) was used. MTS 20 is a compact electro medical apparatus, portable with a good design realized inside a suitcase, conceived for electro stimulation, ionophoresis, TENS, magnetotherapy, ultrasound therapy and laser therapy. In our study, the MTS 20 device was used to deliver the magnetic field with a frequency of 10 Hz, intensity 60 G and applied for a duration of 30 minutes. To check the validity of the magnetotherapy apparatus, the machine was calibrated at the Faculty of Science. Cairo University using Flux meter type T2B HEME AC He Me.

 

Statistical Analysis:

The statistical analysis was done using an IBM compatible computer. Data were included in a database and analyzed by means of  Microsoft Office Excel XP Windows. Descriptive statistics were presented as means ± standard deviations and number percentage. Analytical tests used included unpaired student t test (two sided) for comparing means of two groups and Chi-square test: for qualitative data. The significance level was P<0.05 and P<0.001 was considered highly significant.

 

RESULTS

 

                A decrease in the mean value of the H reflex amplitude immediately after application of the LPMF and remained at the same level after 30 min (P=0.4) was noticed but was statistically insignificant. Also, there was no statistically significant difference in the H/M ratio between the pre and post pulsed magnetic therapy (P=0.7) (Table 1).

        No significant changes were also obtained in H reflex amplitude and in the H/M ratio among the control group (Table 2).

   There was no statistically significant difference in the H reflex amplitude or H/M ratio between both groups in the pre- test value (P= 0.2) or in the post -test values (P=0.6) (Table 3).   

    No statistically significant difference was found between the mean value of the H-reflex latency  pre- and post-application of the LPMFT either immediately after or after 30 min of application (P=0.1) (Table 4).

    On the other hand, a high statistically significant  decrease in the  mean value of the H- reflex intensity threshold was noticed in the present study between before the application of LPMFT and immediately after application and it was maintained at this intensity for 30 min (P= 0.0001) (Table 5).


Table 1. The effect of LPMFT on the H reflex amplitude and H/M ratio in the study group.

 

Item

H amplitude

H/M ratio

Pre-test

Post-test

After 30 min

Pre-test

Post-test

After 30 min

X ±SEM

5.4±0.9

5.1±0.8

4.7±0.7

26.8±3.8

25.7±3.6

24.6±3.5

F

0.84

0.29

P

0.43

0.74

% of change

-4.7% (I.M. after)

-12.4%  (after 30 min)

-4.3% (I.M. after )

-8.3% (after 30 min)

X: mean                   SEM: standard error of mean       F: ANOVA                  P: Probability             IM:  immediately           

 

 

Table 2. Evaluation of H- reflex amplitude and H/M ratio in the control group.

 

Parameter

1st time

2nd time

MD

% of

Change

t-value

P

X±SEM

X±SEM

H amplitude

3.5±0.7

5.3±1.0

-1.7

49.5

1.5

0.1

H /M ratio

23.9±3.0

35.9±6.

11.9

49.8

-1.7

0.1

X: mean                 SEM: Standard error of mean          MD: Mean Difference        t value: Paired t value           P: Probability   

 

 

Table 3. Comparison of H reflex amplitude and H/M ratio in both groups.

 

Parameters

H- amplitude

H/M ratio

Study Group

5.4±0.9

26.8±3.8

Control Group

3.5±0.7

23.9±3.03

T  value

1.2

0.50

P

0.2

0.6

t- value: unpaired t value                                  P: Probability

 

 

 Table 4. Effect of the LPMF on the H reflex latency in the study group.

 

Item

H- latency

Pre-test

Post-test

After 30 min

X ±SED

29.9±0.8

31.04±0.6039

31.4±0.7

F

2.39

P

0.10

% of change

(IM. post)               3.55

(after 30 min)      4.75

X: Mean                 I.M: Immediately             SEM:  Standard error of mean           %: Percent             F: ANOVA          P: Probability        

 

 

Table 5. Effect of LPMFT on the H reflex intensity threshold in the study group.

 

Items

H- threshold intensity

Pre test

Post test

After 30 min

X ±SED

21.3±2.3

15.8±1.6

15.8±1.6

F

11.8

P

0.0001

% of change

-25.56% (IM)

-25.82%( after 30 min)

X: Mean *: Significance    SEM: Standard error of mean   IM: Immediately           P: Probability        F: ANOVA         %: Percent

 


DISCUSSION

 

Low pulsed magnetic field (LPMF) is a very effective biophysical modality used for therapeutic purposes as well as in the area of diagnosis.9

Researchers investigated the effect of different frequencies of the LPMF and reported conflicted results concerning the effect of each frequency. Krause and Straube10 stated that the effect of applied low pulsed magnetic field at different frequencies 20, 15, and 10 Hz on patients with increased muscle tone was frequency independent as there was no difference between the three frequencies and found a significant decrease in the muscle tone compared to the control one. While in 2003, Pawluk11 concluded that application of LPMFs with frequency ranging from 5 to 25 Hz causing the membrane to be lowered to a hyper-polarized level of -90 mV resulted in sensory block.

Our findings indicate that the LPMF at 10 Hz with intensity of 60 G could produce no statistically significant changes in the H-reflex amplitude, H/M ratio or in the H-reflex latency. These could be explained by the fact that LPMF did not result in changes in the cell membrane potentials or the trans-membrane current flow and the magnetic field could affect the component processes equally and oppositely resulting in the appearance of no effect.12

On the other hand, other studies have revealed that LPMF at 10 Hz had an effect on the motor neuron excitability and this was attributed to an increase in the chemical neurotransmitter and a decrease of  the pre-synaptic inhibition of 1a fibers.13

In our study, the H-reflex amplitude was insignificantly decreased immediately after the application of the LPMF while it has no effect on the H/M ratio, that may be attributed to the weak effect of the low pulsed magnetic fields which was not enough to support the changes in the cell membrane to enhance the excitability and were not enough to produce the firing of the action potentials or change the resting membrane potentials.

The exposure to the low pulsed magnetic field can cause reversible blockade of the action potential firing (block firing of sodium-dependent action potentials of sensory neurons) and also reduction of responses to the pain and magnetic field has the ability to induce conformational changes in the ion channels and/or neuronal membrane and these multiple mechanisms must be acting simultaneously.14

Healthy subjects may be fundamentally different from people with   neuromuscular diseases concerning how they are influenced by the LPMFT. This can be due to the instability of the cell membrane that may occur in pathological conditions that will lead to the lowest amount of stimulation needed to produce depolarization and firing of the action potentials.

In comparing the H reflex amplitude and H/M ratio between groups, we found that there was no statistically significant difference between them (P=0.6)  which seemed to be due to the competence of the LPMF to produce sufficient effect on the cations flow to fire and evoke an action potential, therefore the H- reflex amplitude was not changed significantly.

As regards to the effect of the LPMFT on the H reflex latency.  there was no statistically significant changes in the H-reflex latency (P<0.1)immediately after the application of the LPMFT or after 30 min of the application, that might be attributed to the local effect of the LPMF that was inadequate to affect the H reflex pathway.

These findings are in agreement with Hong et al.15 results, who reported that there was no change in the distal latencies or amplitude of the compound muscle action potentials (CMAP) after application of the magnetic field.

In the present study we found a highly statistically significant decrease in the H-reflex intensity threshold in the study group (P<0.0001). This reduction occurred immediately after exposure and lasted for 30 min after application of the LPMFT and this could be interpreted as an increase in the excitability of the motor neuron in the study group. Also, this might be due to an increase in the resting membrane potential of the cell membrane, moreover, the induced current of the LPMF  increased the threshold level of the cell membrane.     

Our finding  was supported by the statement of most researchers16,17, who had proposed that exposure to time varying magnetic field induces electric current in the tissue that affect the resting membrane potentials, increasing its depolarization level which enhances impulses propagation.

Also, Rosen et al.18 assumed that the magnetic field acts on the phospholipids or other constituents of the nerve membrane and make some of the molecules rotate to the direction of maximal susceptibility because of the magnetic anisotropic nature, and this in turn induces change in the membrane properties, rather than a direct effect on the action potentials.

The results of our study can be used in studies of people with central nervous system CNS) pathology and also provide physiotherapists with an effective modality in decreasing αMN excitability. 

 

REFERENCES

 

1.          Rock H, Giesen V, Benecke R. On the origin of the post excitatory inhibition seen after transcranial magnetic brain stimulation in awake human subjects. Exp Brain Res. 1993; 94: 489-98.

2.          Cabre AV, Oliveri M, Gangitano M, Pascual-Leione A. Modulation of spinal cord excitability by subthreshold repetitive transcranial magnetic stimulation of the primary motor cortex in humans. Neuroreport.  2001; 12(174): 3845-8.

3.          Fadiga L, Craighero L, Dri G, Facchin P, Destro MF, Porro CA.   Corticospinal excitability during painful self-stimulation in humans: a transcranial magnetic stimulation study. Neurosci Lett. 2004; 361: 250-3.

4.          Weintranb MI, Cole SP. Pulsed magnetic field therapy in refractory neuropatheic pain secondary to peripheral neuropathy: electro diagnostic parameters- pilot study. The American Society of Neurorehabilitation. 2004; 18: 42-6.

5.      Bassett CAL. Beneficial Effects of Electromagnetic Fields. J of Cell Biochem. 1993; 51: 387-93.

6.           Koelman JH, Bour LJ, Hilgevoor AA. Soleus H reflex tests and clinical signs of the upper motor neuron syndrome. J Neurol Neurosurg Psychiatry 1993; 56(7): 776-81.

7.          Aminoff MJ.   Electromyography in clinical practice, 3rd edition. Churchill Livingstone, New York, London, Tokyo; 1998. p.544-52.

8.          Middleton JW, Siddall PJ, Walker S, Molloy AR, Rutkowski SB. Intrathecal clonidine and baclofen in the management of spasticity and neuropathic pain following spinal cord injury: a case study. Arch Phys Med Rehabil. 1996 Aug; 77(8): 824-6.

9.          Weaver JC. Understanding conditions for which biological of noionizing electromagnetic fields can be expected. Bioelectrochemistry. 2002; 59(1-2): 207-16.

10.       Krause P, Straube AA. Reduction of spastic tone increase induced by peripheral repetitive magnetic stimulation is frequency independent. Neuro-rehabilitation. 2005; 20(2): 63-5.

11.       Pawluk W. Pain management with pulsed electromagnetic field (PEMF) treatment. American Pain Society. 2003 Mar; 20(2): 23-32.

12.       Sonnier H, Kolomytkin OV, Marino AA. Resting potential of excitable neuroblastoma cells in weak magnetic fields. Cell Mol Life Sci. 2000; 57: 514-20

13.    Panagopoulos DJ, Kaeabarbounis A, Margaritis H.  Mechanism for action of electromagnetic fields on cells. Biochemical and Biophysical Research Communications. 2002; 298: 95-102.

14.       Segal NA, Toda Y, Huston J, Saeki Y. Two Configurations of static magnetic fields for treating rheumatoid arthritis of the knee: A double blind clinical trial. Arch Phys Med Rehabilitation. 2001 Oct; 82(10): 1453-60

15.       Hong  ZC,  Harmon D, Yu  J. Static magnetic field influence on rat tail nerve function. Arch Phys Med Rehabil. 1986; 67: 746-9.

16.       Hong C-Z, Lin JC, Bender LF, Schaeffer JN, Meltzer RJ, Causin P. Magnetic necklace: its therapeutic effectiveness on neck and shoulder pain. Arch Phys Med Rehabil. 1982; 63:462-6.

17.       Liboff AR, Jenrow KA. Physical mechanisms of neuroelectromagnetic therapies. Neuro-rehabilitation. 2002; 17(1): 9-22.

18.       Rosen AD. Mechanism of action of moderate intensity static magnetic fields on biological systems. Cell Biochem Biophys. 2003; 39(2): 163-73.

 

الملخص العربي

 

تم إجراء هذا البحث لدراسة تأثير التيار المغناطيسي  المتردد المنخفض على استثارت الخلية العصبية الحركية للأشخاص الأصحاء وذلك من خلال قياس رد الفعل لهوفمان, معدل تغيير المدى لهوفمان بالنسبة لمعدل تغيير رد فعل العضلة, كمون رد الفعل وكذلك شدة التيار. وقد أجريت هذه الدراسة في كلية العلاج الطبيعي جامعة القاهرة في المدة من ديسمبر 2005 حتى مارس 2006.

وقد تم إجراء هذا البحث على ثلاثين شخصا ذكرا طبيعيين وخاليين من الأمراض العصبية والذين تتراوح أعمارهم ما بين (18-27) بمتوسط (1.86955±21.66) و أوزانهم ما بين (55-98) بمتوسط (11.32±70.525( وأطوالهم ما بين (162-188) بمتوسط (6.7429±174.53) وقد تم تقسيمهم عشوائيا إلى مجموعتين. المجموعة التجريبية: تحتوى على 20 شخص, يوضع المجال المغناطيسي على سمانة الرجل اليمنى بتردد 10 هرتز وشدة 60 جوز لمدة 30 دقيقة ويقاس رد الفعل لهوفمان, معدل تغيير المدى لهوفمان بالنسبة لمعدل تغيير رد فعل العضلة, كمون رد الفعل وكذلك شدة التيار قبل التطبيق, بعد التطبيق مباشرة وبعد ثلاثين دقيقة بعد التطبيق المجموعة الضابطة: تحتوى على عشرة أشخاص ويقاس رد الفعل لهوفمان, معدل تغيير المدى لهوفمان بالنسبة لمعدل تغيير رد فعل العضلة, كمون رد الفعل وكذلك شدة التيار قبل وبعد   ثلاثين دقيقة فقط. عولجت النتائج إحصائيا باستخدام الإحصاء التو صيفي والتحليل للاختلاف ذو الاتجاهين لاختبار الفروق في كل مجموعة عند وقت القياس وبين المجموعتين خلال كل وقت محدد للقياس عند مستوى ثقة 0.05

 

 

نستنتج من هذه الدراسة:

1.         وجود فروق ذات دلالة إحصائية على شدة التيار لهوفمان بعد التطبيق وعلى مدى ثلاثين دقيقة بعد التطبيق حيث مستوى الثقة <. 001 ¸.

2.         لم توجد فروق ذات دلالة إحصائية على رد الفعل لهوفمان, معدل تغيير المدى لهوفمان بالنسبة لمعدل تغير رد فعل العضلة و كمون رد الفعل في المجموعة العلاجية.

3.     لم توجد فروق ذات دلالة إحصائية على رد الفعل لهوفمان, معدل تغيير المدى لهوفمان بالنسبة لمعدل تغير رد فعل العضلة, كمون رد الفعل وكذلك شدة التيار في المجموعة الضابطة.

4.     لم توجد فروق ذات دلالة إحصائية بين تطبيق التيار المغناطيسي المنخفض المتردد على رد فعل هوفمان, معدل تغيير المدى لهوفمان بالنسبة لمعدل تغير رد فعل العضلة, كمون رد الفعل وكذلك شدة التيار بين المجموعة العلاجية والمجموعة الضابطة.

 

الخلاصة التي يمكن استنتاجها من الدراسة:

1.         استخدام التيار المغناطيسي منخفض التردد يزيد من نشاط الخلية العصبية الحركية.

2.         استخدام التيار المغناطيسي منخفض التردد في حالات ضمور الأعصاب والعضلات.

3.         استخدام التيار المغناطيسي منخفض التردد في أمراض الجهاز العصبي المركزي التي ينتج عنها ضعف في العضلات الطرفية. 



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