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The effect of transcutaneous electrical nerve stimulation at acupuncture points on spinal motor neuron excitability in people without known neuromuscular diseases.

INTRODUCTION

Patients with upper motor neuron syndrome (eg, a lesion of the central nervous system stroke, spinal cord lesion) often display spasticity [1-7], a complex motor disorder characterized by a velocity-dependent increase in muscle resistance to passive stretch with exaggerated tendon jerks, caused by hyperexcitability of the stretch reflex [8]. Commonly associated symptoms include impaired movement, painful muscle spasms, stiffness and disturbed sleep. Severe or long-standing spasticity may lead to contractures and joint ankylosis, which can severely restrict the patient's care and rehabilitation [9]. Therefore, an effective treatment is important to increase the motor function, facilitate self-care and decrease painful, harmful effects of spastic contractions. Therapeutic treatments, including pharmacological agents and physical therapy, have been used to ameliorate spasticity. However, pharmacologic reduction of spasticity is often associated with severe side effects including sedation, generalized muscle weakness, and hepatotoxicity [10]. Therefore, physical therapy is getting more and more attention in the management of spasticity.

The Hoffmann (H] reflex is widely acknowledged as an indirect indicator of spinal motor neuron excitability. It is well documented that any changes in H-reflex amplitude, latency and recovery time reflect the changes in spinal motor neuron excitability [8,11,12]. Acupuncture is considered an effective therapeutic modality for a wide range of diseases and conditions in Eastern cultures. Western interest in acupuncture is generally related to the treatment of pain [13-15]. In addition to its use in pain management, the scope of research using this modality has broadened considerably to many other medical problems including cardiovascular related medical problems [16], HIV [17], central nervous system ischemia [18] and stroke [19]. Several studies [11,12] have found that the use of acupuncture can alter the sensitivity of spinal motor neuron excitability as evidenced by the changes in H-reflex. Yu and associates [11] have shown that acupuncture at the points of Yang Ling Chuan, Hsuan Chung, Kun Lun, Feng Shih and Cheng Shan can prolong the H-reflex recovery time following the double-stimulation of poplitial tibial nerve in stroke patients with the paralysis of the lower limb. Our previous results demonstrated that low intensity TENS increases H-reflex amplitudes in subjects without known neuromuscular diseases while high intensity TENS had little influence on H-reflex amplitudes [8]. A recent study from Ge at al. shows that TENN at intramuscular trigger points increases H-reflex [29]. A study from Chang at al. shows that TENS with surface electrodes on Hegu acupoint increases the amplitude of the H-reflexs [12]. However, the changes in H-reflex in soleus in response to the acupoint stimulation on Hegu (in the hand) could be different from the H-reflex response following the acupoint stimulation in the leg. The effect of TENS, administered via non-invasive surface electrodes to acupoints in the leg, on H-reflex of the soleus muscle has not been previously studied. Therefore, the main purpose of the present study is to determine the effect of TENS, administered to acupuncture points, on spinal motor neuron excitability, as reflected by the H-reflex of the soleus muscle, in volunteers having no known neuromuscular diseases. Despite numerous studies, demonstrating that TENS can alter the H-reflex response, considerable controversy exists regarding the effect of stimulus intensity on the H-reflex. Some authors [20,21] reported that that hypertonicity and tonus decreases when TENS was below sensory threshold (ST). Other authors [22-24] have suggested that the stimulation should be above ST and just below motor threshold (MT). Stimulus intensity also varies in people with no known muscular diseases. Our previous results [8], along with the study from Delwaide and associates [25], have shown that mild stimulus increases the amplitude of H-reflex of the soleus muscle whereas a strong stimulus caused no changes or a brief decrease in the H-reflex. However, other authors [26] have observed that a mild stimulus caused a decrease in the soleus muscle's H-reflex. In the present study we focused on the potential differential effects that stimulus intensity at the acupuncture points might have on this reflex. Our hypothesis is that TENS at the acupuncture points will influence the H-reflex in healthy subjects and that this influence will vary in magnitude depending on the stimulus intensity.

METHODS

Subjects: This study was conducted on 45 [26 males, 19 females) volunteer subjects, with no known neuromuscular disease, with an age range from 21 to 47 years old. Subjects were informed of the nature of the experiment, benefits and risks involved in participation, and all signed an informed consent document. Subjects were randomly divided into 3 groups determined by TENS stimulus intensity as follows: control (C), sensory threshold (ST), and 1.5 ST. The demographics of our study are illustrated in the table below:

Groups     Males   Females   Total #   Mean Age

Control    11      5         16        24.43
ST         8       7         15        25.33
ST 1.5     7       7         14        25.21
Totals     26      19        45        24.98


H-reflex protocol. H-reflex recording performed by an experienced EMG technologist, using a commercially available electrodiagnostic apparatus (Viking IV-D). First, an H-reflex recruitment curve recorded to determine the current necessary to produce a maximal H-reflex and a maximal M-wave (short-latency orthodromic motor response). The current were subsequently adjusted to elicit reproducible H-reflexes that measured between 20% and 40% of the maximum M-wave, a size known to be sensitive to both excitatory and inhibitory influences [27]. Following this procedure, 10 H-reflexes recorded in complete relaxation before and 3 times after TENS. An H-reflex evoked every 10 seconds using a 1-millisecond stimulus duration.

TENS stimulation apparatus: Transcutaneous electrical nerve stimulation administered with a Grass S-88 stimulator [Grass instruments, Division of Astro-Med Inc, 600 E Greenwich Ave, West Warwick, RI 02893) through 4 carbon-rubber surface electrodes [4.3 cm long x 3.7 cm wide or 1.25 inches in diameter) at the acupuncture points. The stimulus delivered as 3-second trains, with a 2-second intertrain (off) period. Each train consisted of 100-microsecond square waves occurring at 20 Hz [total of 60 pulses). These stimulus parameters were similar to those used to reduce spasticity, hyperreflexia, and clonus [1,2,4,8,22,28] using these stimulus settings, each subject tested to determine the sensory or 1.5 times ST at the following four acupuncture points of Yang Ling Chuan, Kun Lun, Feng Shih and Cheng Shan as previously described [11]. The TENS administered either at ST or at 1.5 times ST (1.5ST), depending on a group assignment.

Experimental protocol: Subjects were randomly assigned to one of three groups (control, ST stimulation and 1.5 ST stimulation groups) in which electrical stimulation administered for 15 minutes. The subjects in the control group had the electrode placement as the two experimental groups, but did not receive electrical stimulation. The subjects in the ST stimulation group received electrical stimulation at the acupuncture points with stimulation intensity at the level of ST. The subjects in the 1.5 ST group received electrical stimulation at the acupuncture points with stimulation intensity at the level of 1.5 ST. Immediately before the period of electrical stimulation, 10 consecutive H-reflexes elicited, and their amplitudes averaged to yield the baseline value. Following the period of stimulation, 3 sets of 10 H-reflexes each obtained starting (1) at the end of stimulation, (2) five minutes following the end of stimulation, and (3) ten minutes following the end of stimulation.

Data Analysis: Repeated ANOVA test were used to compare the statistical significance between the groups and the differences before and after electrical stimulation. Data were expressed as means [+ or -] SE.

RESULTS

There was a significant increase (P < 0.05) in H-reflex response following transcutaneous electrical stimulation at sensory threshold and 1.5 sensory threshold levelsat acupuncture sites.

There was more of an increase in H-reflex response following stimulation at 1.5 sensory threshold levels.

DISCUSSION

We have investigated the effect of TENS with ST and 1.5 ST at acupuncture points on the lower limb on Hreflex. In our study, the results supported the hypothesis that stimulus intensity would play an important role in determining the extent to which TENS influenced the H-reflexes. In subjects with no known neuromuscular diseases, we found that low-intensity TENS at acupuncture points increased H-reflex amplitudes; high-intensity stimulation at acupuncture points caused significant higher increase in amplitude of H-reflex.

These results tend to be in partly agreement with the research findings from Delwaide and associates [25] in which they found that mild stimulation (2-3 times ST) of the sural nerve caused a brief increase of the soleus muscle's H-reflex, whereas a strong (painful) stimulus caused a brief decrease of the soleus H-reflex. The observations of Delwaide and associates[25] correlate well with our findings that TENS delivered at ST resulted in an increase in the soleus muscle's H-reflex, whereas TENS delivered at 1.5 ST caused an higher increase in amplitude of H-reflex.

The fact that our results only partly support the findings of Delwaide and associates [25] may be attributed, in part, to the fact that we used different intensity. Delwaide and associates [25] used painful stimulus as higher stimulation intensity as compared to 1.5 ST as high stimulation intensity used in the present study. At 1.5 ST, subjects felt strong, but not painful. Therefore, our data seem to indicate that TENS utilizing a strong stimulus, but not painful, significantly increased the amplitude of H-reflex.

The present study results also confirmed our previous findings [8] at which low intensity TENS increased amplitude of H-reflex, but high intensity TENS did not alter the amplitude of H-reflex. The possible explanation for the difference between the present study and our previous study is the difference in stimulation sites. The present study used acupuncture points as compared to non-acupuncture points used in our previous study. Acupuncture points may be more sensitive than non-acupuncture sites. Further research required to confirm our hypothesis.

In summary, the present study results indicate that both of the low and high intensity TENS at acupuncture points increase H-reflex amplitudes in subjects without known neuromuscular disease.

CONCLUSION AND CLINICAL IMPLICATIONS

This study shows that TENS at acupuncture points results in an increase in H-reflex response. As patients diagnosed with stroke [cerebral vascular accident) often present with flaccidity and decreased H-reflex response, TENS at acupuncture points could potentially be used clinically to increase H-reflex response and ultimately decrease flaccidity.

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Min Huang (1), Howe Liu (1), Jian-Wei Gu (2), Ham Benghuzzi (1), Xuexiang Wang (2), Antonio V Hayes (3), Rebecca H. Pearson (1), Felix Adah (1), and Dobrivoje S Stokic (3).

(3) Neurophysiological Research Laboratories, The Methodist Rehabilitation Center, Jackson; (2) Department of Physiology, and (1) department of Physical Therapy, University of Mississippi Medical Center, Jackson, MS
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Author:Huang, Min; Liu, Howe; Gu, Jian-Wei; Benghuzzi, Ham; Wang, Xuexiang; Hayes, Antonio V.; Pearson, Reb
Publication:Journal of the Mississippi Academy of Sciences
Article Type:Report
Geographic Code:1USA
Date:Apr 1, 2014
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