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Table of Contents
ORIGINAL ARTICLE
Year : 2016  |  Volume : 4  |  Issue : 2  |  Page : 7-13

Difference in sensory, motor and pain threshold for medium frequency electrical stimuli in different pain conditions-A pilot study


1 Lecturer, The Sarvajanik College of Physiotherapy, Surat, Gujarat, India
2 Graduate Physiotherapists, The Sarvajanik College of Physiotherapy, Surat, Gujarat, India

Date of Web Publication30-Aug-2018

Correspondence Address:
A Thangamani Ramalingam
Lecturer, The Sarvajanik College of Physiotherapy, Surat, Gujarat
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2347-6486.240206

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  Abstract 


Background: Different current frequencies are considered to produce a different reaction in tissues. But there is still a lack of knowledge about the reactions of tissues on medium frequency electric currents with different frequencies in special groups of diseases or trauma.
Objective: The main objective of the study was to find out the difference of physiological response between normal healthy, chronic low back pain and postoperative pain subjects for a medium frequency (4 KHz) electrical stimuli with 20, 50 and 100 Hz base frequencies.
Method: Readings were taken for sensory, motor and pain threshold with three different frequencies 20 Hz, 50 Hz & 100 Hz for normal healthy, chronic low back pain and postoperative pain subjects. Electrodes were applied over the dorsal and ventral side of the ankle in all the maneuvers. For the normality of the data, Shapiro-wilk test was done. Statistical analysis was done using IBM SPSS version 20.0 and significance were set at “p<0.05”.
Result: A multivariate ANOVA test showed significant difference statistically between groups; sensory and the motor threshold for back pain was less than normal and postoperative subjects, irrespective of the frequencies used for stimulation. The post hoc analysis between groups showed that chronic low back pain subjects differ from normal individuals in pain threshold (difference 1.617mA, p=.041).
Conclusion: The sensory and motor response threshold was more in acute pain subjects and in normal individuals than chronic low back pain subjects. Reduced sensory motor threshold and increased pain threshold in chronic back pain subjects may indicate hyperalgesia and perceptual delay in processing of the electrical stimuli by the nerves system.

Keywords: sensory, motor, pain threshold, medium frequency stimuli


How to cite this article:
Ramalingam A T, Mayuri A P, Vidhi H M, Bhumika S T, Hardik B P. Difference in sensory, motor and pain threshold for medium frequency electrical stimuli in different pain conditions-A pilot study. J Integr Health Sci 2016;4:7-13

How to cite this URL:
Ramalingam A T, Mayuri A P, Vidhi H M, Bhumika S T, Hardik B P. Difference in sensory, motor and pain threshold for medium frequency electrical stimuli in different pain conditions-A pilot study. J Integr Health Sci [serial online] 2016 [cited 2021 Dec 3];4:7-13. Available from: https://www.jihs.in/text.asp?2016/4/2/7/240206




  Introduction Top


Bioelectricity is the electrical phenomenon of life processes. The electrical current is the external stimulus that initiates the action potential along the length of the nerve.[1],[2] The electric conductivity of the body depends on the type of the tissue like muscle, fat, skin and on the electrolyte and water concentration in the tissues.[3] The impedance is dependent on the frequency of the stimulating current. The higher the frequency of the current is the lower the impedance is. So currents using medium–frequency output (1000 - 10 000 Hz, as the carrier frequency of interference current) are suitable for therapy because the use of higher intensity is possible without the irritation of the tissues. An external therapeutic current has effects on the cellular and tissue level, on the segmental level and the whole system. In nerve the order of reactions prevails regardless the waveform, pulse rate or electrode size, when distances between nerve fibers and the electrode are approximately the same.[4],[5] The sequence of the sensory, motor and pain thresholds excitation reactions when different frequencies are used, is not to be changed , but clinical experiences have shown difference.[6]

The point at which a stimulus triggers the start of an afferent nerve impulse is known as a threshold. Thresholds are measured by gradually increasing the intensity of a stimulus such as electric current or heat applied to the body. Sensory threshold means the level that must be reached for an effect to be produced, as the degree of intensity of a stimulus that just produces a sensation. Motor threshold means the minimal stimulus that produces excitation of any structure, eliciting a motor response. The recruitment threshold means the stimulus intensity at which a motor unit begins to fire is reached, it fires fully. Pain threshold is the point at which the stimulus begins to hurt, and the pain threshold is reached when the subject acts to stop the pain. Differences in pain perception and tolerance thresholds are associated with factors such as ethnicity, genetics, and gender.[7],[8],[9]

Alternating currents of medium (>l kHz to <10 kHz) frequency meet little resistance and penetrate the tissues easily, although such currents generally oscillate too rapidly to stimulate the tissues directly. Interferential current is one type of a medium frequency alternating current.[10] Variable -frequency oscillator can sweep automatically between one pre-set frequency and another, thus producing a range of beat frequencies as a result of constructive interference.[11] Prolonged stimulation at a supramaximal frequency will cause the axon to cease conducting. Accommodation of the neuron is responsible for this effect, and it is caused by an increased threshold and synaptic fatigue’.[12],[13] With medium-frequency currents, a higher proportion of electrical energy is available to stimulate tissue under the superficial epidermis. This can be particularly important when motor nerves, which are deeper, be stimulated.[14] The stimulus intensity required at different frequencies to elicit sensory, motor, and pain thresholds. These thresholds provide an empirical basis for selecting carrier frequencies for specific purposes. For example, if there is only a minimal separation at a particular frequency between the motor and pain thresholds, the intensity of current sufficient to produce motor stimulation is quite likely to cause pain. A larger separation between thresholds suggests a preferable frequency for clinical uses.[15]

Different current frequencies are considered to produce a different reaction in tissues. There is still a lack of knowledge about the reactions of tissues on electric currents with different frequencies in special groups of diseases or traumas expressed as sensory and motor thresholds. For this purpose alternating current of a variable beat, frequencies were given into human tissues for measuring sensory, motor and pain threshold reactions using the method which is called frequency analysis method –FAM.[15] Hence the aim of the study was to evaluate any differences in physiological threshold responses between normal healthy adults, chronic back pain Subjects and acute post -operative pain Subjects.


  Methodology Top


Subjects

An observational pilot study used non-probability prospective sampling collected data from 20 postoperative pain subjects, 20 normal individuals and 20 chronic low back pain Subjects between the ages of 18 to 65years who were willing to give consent. Patients who have undergone laparotomy and receiving the postoperative care immediately thereafter ; patients who were suffering from low back pain for more than six months duration ; and normal healthy individuals without any major illnesses were included in the study. Subjects with any other major illnesses such as trauma, myopathy, neuropathy, epilepsy and diseases which may alter the physiological responses were considered for exclusion.

Tools

Interferential therapy equipment-VECTROSTIM from techno med electronics, Chennai with serial no 341 with medium size rubber electrodes was used to produce medium frequency stimuli with different frequencies.

Procedure

For the present study the subjects were taken from Lockhat hospital and Sarvajanik college of physiotherapy, Surat according to our inclusion and exclusion criteria and who gave consent to participate in the study. The study was conducted after the permission and approval from the hospital authority. Readings were taken for sensory, motor and pain threshold using three different amplitude-modulated frequencies (AMF) or base or beat frequencies 20 Hz, 50 Hz and 100 Hz with 4 kHz interferential current (alternating current) for all the three groups. For this, the subjects were asked to lie on a plinth and electrodes were fixed on dorsum and plantar aspect of the foot. Then the intensity of the machine was increased slowly on” 1” point basis and the subject was asked to inform the feel of current, the intensity of the machine was noted (sensory threshold) and further when the experimenter perceived the movement of the foot, intensity noted (motor threshold). The current was given further to find out pain threshold when subject self-reported discomfort for a particular intensity (pain threshold). The above said procedure was done for normal healthy individuals and chronic low back pain patients at their first visit; And for postoperative pain cases it was done after 48 hours of surgery.

Data analysis

A multivariate ANOVA was used as primary statistical analysis for Between-group and within- group comparisons. All the analysis was done using IBM SPSS statistics for windows, version 20.0. Armonk, NY: IBM corp. Statistical significance was set at “p<0.05”for all statistical analyses.


  Results Top


The current study included three groups of normal individuals (N=20), chronic low back pain subjects (N=20) and post-operative pain subjects (N=20). [Table 1] and [Figure 1],[Figure 2],[Figure 3] show shows the mean and standard deviations of sensory, motor and pain threshold for 20 Hz, 50 Hz and 100Hz frequency electrical stimuli of normal, chronic low back pain and post- operative pain subject groups. [Table 2] shows the multivariate ANOVA test analysis. It shows that sensory and motor thresholds are different between groups and no difference in pain threshold. And between the different base frequencies no difference in sensory, motor and pain threshold. [Table 3] shows the post hoc analysis between groups. And the result showed that chronic low back pain subjects differ from normal individuals in pain threshold also (difference 1.617mA, p=.041).
Table 1: Mean and standard deviations for different threshold (N=20)

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Figure 1: sensory threshold for different frequencies for the groups

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Figure 2: motor threshold for different frequencies for the groups

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Figure 3: pain threshold for different frequencies for the groups

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Table 2: Multivariate analysis of variance test

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Table 3: Post hoc analysis between groups

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  Discussion Top


The current study attempted to find out the difference between sensory, motor and pain threshold among normal, chronic low back pain and acute post- surgical pain subjects. The comparison of the all the three groups showed sensory, the motor threshold for back pain is statistically different from normal individuals and postoperative pain subjects. But pain threshold remained different with normal subjects. All the three thresholds remained same irrespective of the base or beat frequency used for stimulation.

The sequence of the sensory, motor and pain thresholds has been presented by many researchers. The present study results are in support to the result of Lehtela et al that tissues would react differently when stimulated with different frequencies in a different group of subjects Characteristic differences of persons with health problems should be confirmed with further testing.[3],[4] In one study it was mentioned studies tried to establish the values of sensory, motor and pain of thresholds in the human body and to find out which frequency is good for treatments of a different group of subjects.[13] A likely explanation is that different nerve fibre types have different refractory periods, different periods of hypo- and hyperexcitability, and different recovery times for a medium frequency stimulation.[16],[17]

This raises a question that the chronic back pain subjects have hypersensitivity (hyperalgesia). The pain threshold for chronic back pain was little more compared to normal individuals and postoperative pain subjects (no statistical difference). Is it due to perceptual delay due to chronic pain suffering? Or due to peripheral nervous system delay? Moreover, the beat frequencies commonly used in Inferential current treatment may be a cause for over excitation of the nerves tissues respective of the pain condition of the subjects. So it is very important to find out the subgroup of patients with hyperexcitability before applying electrical currents as a treatment modality. As the study used small sample size could be a reason not able to generalize the results. A large sample size study could provide more insight in this context.


  Conclusion Top


The sensory and motor response threshold was more in acute pain subjects and in normal individuals but was less for chronic low back pain subjects. Reduced sensory motor threshold and increased pain threshold in chronic back pain subjects may indicate hyperalgesia and perceptual delay in processing of the electrical stimuli by the nerves system.



 
  References Top

1.
J E. Bioelectric phenomenon. In: Introduction to biomedical engineering. Elsevier, Oxford, UK2004.  Back to cited text no. 1
    
2.
Watson T. Electrotherapy, evidence-based practice. Churchill Livingstone2010.  Back to cited text no. 2
    
3.
Lehtelä MM, PT, et al. The Frequency Analysis Method – The FAM - a novel tool in physiotherapy for assessing physiological responses in human body.  Back to cited text no. 3
    
4.
DeDomenico G. New Dimensions in Interferential Therapy. A Theoretical & Clinical Guide. 1987.  Back to cited text no. 4
    
5.
Nelson RM, Hayes, K W and Currier, D P . Clinical Electrotherapy1999.  Back to cited text no. 5
    
6.
Low JaR, A. Electrotherapy Explained. Principles and Practice. Oxford.2000.  Back to cited text no. 6
    
7.
Melzack R WP. The challenge of pain. New York1996.  Back to cited text no. 7
    
8.
Maffiuletti NA, Herrero AJ, Jubeau M, Impellizzeri FM, Bizzini M. Differences in electrical stimulation thresholds between men and women. Annals of neurology. 2008;63(4):507-12.  Back to cited text no. 8
    
9.
Brodoehl S, Klingner C, Stieglitz K, Witte OW. Age-related changes in the somatosensory processing of tactile stimulation--an fMRI study. Behavioural brain research. 2013;238:259-64.  Back to cited text no. 9
    
10.
Kloth L. Interference current. In: Clinical ElectrotherapyNelson, R.M., Currier, D.P. Norwalk, Connecticut, USA.1987.  Back to cited text no. 10
    
11.
De Domenico G. Basic Guidelines for Interferential therapy. Ryde. NSW. Australia1981.  Back to cited text no. 11
    
12.
Krnjevic KaM, R. Failure of neuromuscular propagation in rats I Physiol 1958.   Back to cited text no. 12
    
13.
AR W. Electricity fields and waves in therapy Marrickville Australia1986.  Back to cited text no. 13
    
14.
JP. R. Electrical stimulation and Electropathology. cambridge1992.  Back to cited text no. 14
    
15.
Ward AaR, V. . ‘Sensory, Motor and Pain Thresholds for stimulation With Medium Frequency Alternating Current’. Archive of Physical Medicine and Rehabilitation. 1998.  Back to cited text no. 15
    
16.
Kiernan MC, Lin CS, Andersen KV, Murray NM, Bostock H. Clinical evaluation of excitability measures in sensory nerve. Muscle & nerve. 2001;24(7):883-92.  Back to cited text no. 16
    
17.
Ward AR, Oliver WG, Buccella D. Wrist extensor torque production and discomfort associated with low-frequency and burst- modulated kilohertz-frequency currents. Physical therapy. 2006;86(10):1360-7.  Back to cited text no. 17
    


    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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