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Electronic implementation of a PWM electrical nerve stimulation system for medical treatment of acute and chronic pains

  • Lamia Bouafif
  • Noureddine Ellouze
Article
  • 98 Downloads

Abstract

In this paper we will implement a transcutaneous electrical nerve stimulation (TENS) designed for medical applications in order to reduce acute and chronic pains. This procedure uses electrical currents pulses applied on the skin area via electrodes. Two kinds of stimulation are adopted: the peripheral nerve stimulation (PNS) and the spinal cord stimulation (SCS). In either, a small pulse generator sends electrical pulses to the nerves (in PNS stimulation) or to the spinal cord (SCS stimulation). Previous studies on TENS technique showed that the obtained results are not very satisfactory and depend on the patient’s state, condition, age, and stimulation parameters. In order to optimize the conditions and parameters stimulation during treatments, we present in this paper a new strategy called pulse width modulation stimulation (PWM-TENS) based on a parametric computing of frequency, current intensity, pulse duration of stimuli. To implement our approach, we used an embedded platform under Arduino-Uno with five several programs depending on the pain category and according to international medical standards and specifications. The first tests on 15 volunteer patients showed satisfaction ratio (EVA) after 5–12 days and a pain reduction between 80 and 20 after 1 month of stimulation. This result is important because it prolongs the analgesic effect and reduces therapeutic rehabilitation period. The medical aspect of the subject is to have a medical tool that allows objective evaluations for short and medium periods of pain treatments with dynamic evaluation metrics.

Keywords

Electric stimulation Pain transmission Gate control Supra spinal TENS implementation 

1 Introduction

Pain is an unpleasant sensory expression that affects the human body and causes physical and mental suffering. Previous studies indicate that up to half the adult population suffers from acute or chronic pains [1]. The nervous system is responsible for pain transmission through the neurons [2]. One of the most known therapeutic techniques to decrease pain is the electrotherapy that uses electrical stimulation of the nerves. Low power currents are applied via electrodes on the surface of the skin and are mainly used in the rehabilitation of nervous system trauma and other neurological indications, physical therapists or physiotherapists [3].

Historically, in 1748 the physicist Jean Jallabert, was the first to use an electrostatic machine sparking applied to a patient with a paralyzed arm [4]. He obtained a significant improvement in directing the discharge of the extensor muscles of the forearm. Later in 1818, Bischoff, professor of pharmacology, used therapeutic electrical device composed of silver electrodes to heal the paralyzed body of one of his patients [5]. Also, the French philosopher René Descartes is the first who suggested that the pain went through very specific paths connecting the skin to the brain. We had to reach the twentieth century to observe real progress in therapeutic medicine through the use of electro stimulation in 1965 by using “gate control” theory developed by Wall and Melzack [6]. The principle is to block the passage of the pain before reaching the brain. Indeed, he showed that stimulation of tactile fibers with large diameter (Aα and β) strengthen the physiological inhibitory mechanisms at the dorsal horn of the spinal cord, limiting the passage of nociceptive impulses from small caliber fibers (Aδ and C) to the supra spinal structures [7].

Several studies are made to test the effectiveness of this new method on patients with moderate and severe pains. In a recent study conducted on patients with a history of recalcitrant postherpetic neuralgia, Malcom showed that tests on a large population give a large superiority and satisfaction of a feedback nerve stimulation therapeutic strategy than the traditional treatment with drugs [8].

Others studies demonstrated the superiority of TENS compared to placebo in low back pain, according to Koes and Fahrer works in 1991. Blasford, Leandri and Faghri showed that TENS effectiveness is useful in the sedation of postoperative pain, scapular pain hemiplegic of epicondylalgia. In 1993, Herrera and Sotosky wrote that TENS efficiency appears comparable to that of ultrasound in periarthritis and polyarthritis. However, the effectiveness of TENS remains potentiated in the low back by association with a motor stimulation as illustrated by Moore in 1997.

Currently, despite the availability on the market of several nerve stimulation devices, however, their results are very uncertain and depend on the patient and adjustments and stimulation parameters.

Even research studies provide sometimes contradictory statistics on either stimulation methods. Systematic reviews suggested that Electric Nerve stimulation is of limited benefit as a standalone pain therapy for acute pain. However, Bjordal et al. re-assessed the evidence and concluded that TENS reduced post-operative analgesic consumption if it was applied using adequate technique [9].

The purpose of this study is optimizing stimulation parameters to best relieve the patient and extend the maximum analgesic effect of the pacemaker. Innovation and added value are to provide a medical tool that allows objective evaluations for short and medium periods of pain treatments. We integrated in the algorithm of PWM TENS several dynamic evaluation metrics (like EVA and TA) thanks to the patient interactivity and evaluation. This tool will assist the doctor (according to physiological data acquisition stored on the device) to evaluate and follow the therapy and physical treatment.

2 Materials and methods

There are currently in unconventional therapeutic medicine two types of anti pain stimulation: gate control stimulation and supra-spinal stimulation.

2.1 Electrical stimulation technique: gate control

This technique is based on the stimulation of large myelinated fibers (Aß) with rapid conduction to block the responses of nociceptive neurons of the dorsal horn induced by stimulation of small fibers Aδ and C characterized by a slow conduction. Figure 1 illustrates the mechanism of this theory. The development of a peripheral origin inhibitor system is made by stimulation of skin fibers with large diameter Aα, Aβ by using a low current and high frequency of 50–100 Hz (Figs. 1, 2). The perceived sensation is a kind of tingling paraesthesia (recruitment of fibers A α), or numbness (recruitment fibers Aβ). The paresthesia felt neither painful nor unpleasant and occurs from 20 to 30 min [10].
Fig. 1

Gate control theory of mechanism

Fig. 2

TENS data acquisition

2.2 Endorphin or supra segmental stimulation

It is applied at the level of the brainstem neurons which are the source of descending inhibitory pathways. They lead by blocking nociceptive reflex analgesia of the affected area with endorphin release [11]. The central inhibition or rather supra spinal pain causes the secretion of neurotransmitters that block the pain receptors. The setting of endomorphinic endogenous systems (β endorphins, Metenképhaline) is made by a stimulation sensitive of (Αδ) which affects muscle vibrations. In this cast, the current intensity must be high with low frequency (1–5 Hz) and the duration session does not exceed 45 min. It was verified that the modulation of cell activity provided support and surround neurons in the spinal cord and can produce analgesia in a spinal segmental level by using the nerve stimulation [12].

2.3 Mechanisms of pain transmission

The nervous system is responsible for the transmission of impulses between nerves and others organs. These nerves are classified into two main categories:
  • The sensory nerves that transmit information of somatic sensory receptors (located in the skin and muscles) and visceral to the central nervous system.

  • The Motor nerves that carry the nerve message to muscles or glands [13].

2.3.1 Electrical excitation potential of nerves

Nerve fibers and muscle fibers are responsible for the transmission of pain. They are excitable by membrane potentials you to action.

*The membrane potential (Fig. 3)
Fig. 3

potential of Na+ and K+ ions

This is the potential difference (pd) of either side of a membrane of an excitable cell: when inserting an electrode within the cell it is found that the internal face of the membrane is negative with respect to a reference electrode placed on the outer surface of said membrane that (pd) is equal to − 70 mV. This potential is of a different ionic distribution of Na+ ions and K+ outside inside, the concentration of K+ and higher than that of Na+ [14].

*Action Potentia (Fig. 4)
Fig. 4

Evolution of the potential PA

When an electrical pulse is applied to a nerve fiber through two electrodes a current depolarizes the membrane part.

If the intensity is not effective, a slight depolarization is observed. If the current intensity increases gradually, the light depolarization increases until it reaches a threshold (− 50 mV) and becomes fast and independent of exciting current: this variation is called the action potential (AP) and has a width of 1–2 ms [15].

2.4 Configuration and parameterization

To utilize the gating effect, transmission of A fibers should be increased without similar increase in transmission of C fibers carrying pain. As (A) fibers respond to a greater extent to phasic input, while C fibers react best to continuous wave forms, the skin surface should be stimulated with phasic input device to stimulate A fibers without disturbing C fibers. This is the basic concept for TENS mode of action.

Figures 5 and 6 illustrate an example of a TENS system with an image of 4 electrodes positions.
Fig. 5

The spinal stimulation device

Fig. 6

Electrodes positions

*Wave forms Parameters

Current TENS models favor the biphasic waveform which can be square, rectangular, sine wave or triangular/spiked. Other medical devices for acute pains use spike waves causing more irritating the skin and requires dynamic movement of electrodes or shorter treatment periods.

Yet, square, rectangular or sine wave are more comfortable for patients because they create less skin irritation and can applied for a long period especially for chronic pains.

*Frequency
  • High frequencies in the range of 80–150 Hz are recommended if the condition is acute, however, lower frequencies in the range of 1 to 20 Hz, are more applicable for chronic pain.

*Pulse width (Duration)

Generally, the pulse width ranges are between 50 and 400 ms. In the case of a normal neuromuscular system, a range of 100–150 ms is recommended, whereas for patients with neurological damage, wider widths are indicated in range of 200–300 ms.

*Amplitude (intensity)

The basic range of TENS currents amplitude are from 1 mA to 100 mA. The low amplitude is more preferable. As the high-amplitude administration offers an immediate relief of pain, being too-short lived as compared with the longer-lasting relief, provided by the lower intensities.

*Modulation of parameters
  • Frequency modulation: 20% periodically (100, 80, 100, 80 Hz, etc.).

  • Pulse width modulation: 25% periodically.

  • Amplitude modulation: 10% periodically.

2.5 Parameters of the TENS electrical nerve stimulation

Transcutaneous electrical nerve stimulation (TENS) is primarily used for pain control in people with acute and chronic pain conditions. TENS devices use adhesive electrodes applied to the skin surface to apply non-invasive pulsed electrical stimuli that can be modified in terms of frequency (stimulation rate), intensity and duration [11]. The effectiveness of the stimulation seems related to the transmitted electric charge. The parameters of TENS stimulation are the wave duration, the current intensity and the signal frequency. The recommended values of these parameters are depending on the pulse frequency (1–100 Hz), the intensity of electric current (0–50 mA), and the width of the pulse (0, 1–0.5 ms). For Electro-analgesia, stimulation is classified into four levels according to their characteristics, such as:
  • Sub-threshold level: The Stimulus is usually not noticeable and has a current intensity of micro amperes.

  • Sensory level: in this case the phase duration is 2–250 μs, the pulse duration: 4–500 μs, the frequency: 50–200-Hz

  • Engine level: Phase Duration: 2–250 μs, Pulse duration: 4–500 μs, Frequency: 1–5 Hz, Amplitude: For a muscle contraction.

  • Painful level: Phase Duration: up to 0.5 s, Pulse length: up to 1.0, Frequency: 1–5 or 15–200 Hz, Amplitude: For a pain perception.

The next Tables 1 and 2 give an illustration of the standard values of the stimulation parameters and their applications.
Table 1

TENS stimulation categories

Stimulation mode

Current waveforms

Parameters

Applications

C-TENS (gate control)

Open image in new window

Stimulation at HF: frequency range (50–100 Hz)

Pulses width: 50–200 μs with low current intensity

Reduces the local pains

But the effects stops at the end of the stimulation

AL-TENS (acupuncture like)

Open image in new window

Stimulation at BF

Frequency range (1–4 Hz)

Pulse width: 100–400 μs with high current intensity

Muscular and engine stimulation

 Diffused pains

 Rapid action

 Analgesic action is maintained even after stimulation

Mixed and hybrid

Open image in new window

Stimulation with medium frequencies (20–80 Hz)

Pulse width: 200–600 μs with high current intensity

Sharp and hard pains

Diffused pains

Temporal and not permanent

Table 2

Standard stimulation parameters

Parameters

Conventional

Low rate: acupuncture-like

Pulse train Burst

Briet intense

Frequency

50–100 Hz

1–4 Hz

Trains of 70–100 Hz modulated at 2 Hz

100–150 Hz

Impulse duration

40–75 μs

150–250 μs

100–200 μs

150–250 μs

Amplitude

Perceptible (10–30 mA)

Muscular contractions (I = 30–80 mA)

Contractions (30–60 mA)

Facial or Titanic contractions (30–80 mA)

Effects

Short duration

Long duration

Long duration

variable duration

3 Protocols

3.1 Treatment procedures

The use of TENS for pain control is advised to be for 1 h (max) per session, four times daily. Prolonged use is also recommended in postoperative use, painful scars and obstetrics [16].

3.1.1 Preparing the patient

Skin in the area of electrode placement should be clean, clear of lesions. A conduction medium (gel or spray) is recommended. Tapes are required to fix electrodes in position to maintain contact throughout the period of stimulation.

3.1.2 Electrode placement

Several techniques are based on nerve root, acupuncture points or trigger points. Although all of these strategies are valuable, they vary with each individual case, as several anatomical points should be established to suit each case.

a) Electrode placement for upper limb
  • Point of pain

  • Tip of acromion.

  • between thumb and forefingers

  • Wrist-watch position

b) Electrode placements for lower limb
  • Gluteus maximus center.

  • Popliteal space.

  • Posterior to lateral malleolus.

  • Head of fibula.

  • Medial/lateral knee.

c) Electrode placements for lower back
  • Gluteus maximum center.

  • Popliteal space.

  • Crossed pattern: Para-vertebral al L1 and L5, in a box-like pattern, with the circuits crossing at L3.

  • Transarthral placements: Shoulder, elbow wrist, knee and ankle joints.

  • Bilateral placement: Midback and low back.

4 Results

Two small electrodes are placed on either side of the area of pain. The higher frequencies tend to block the pain signals, while much lower frequencies will stimulate the body to produce endorphins which naturally reduce pain. TENS Units provide relief with nerve stimulation for back pain, foot pain, shoulder pain, neck pain, and virtually any other acute or chronic pain.

4.1 The stimulator

Transcutaneous electrical nerve stimulation (TENS) is non invasive technique used in pain treatments. Analgesia is made either by strengthening inhibitory mechanisms of the posterior horn (Gate Control) or by excitement centers inhibitors supra spinal (endorphin secretion). For this, we have developed several electro-stimulation programs as exposed in Table 3. Depending on the scope of the stimulation, we can classify TENS into 4 types [17]:
Table 3

TENS modes

 

Frequency (Hz)

Impulsion (μs)

Intensity

Duration

Conventional (program 1)

80 Hz–100

100–200

Modulated lo tingle

30 min

Trigger

ISO

200

High

15 min

Acupuncture (program 5)

4–6

150

High

45 min

Burst (program 2)

HF modulated at 1–4 Hz

150

Medium and moderate

30 min

Mixture

Alternatively 3 Hz and 80 Hz

100

Progressive: moderate lo high

15–20 min

  • Conventional TENS: for immediate analgesia but of relatively short duration.

  • TENS trigger: for local analgesia, quick but fleeting.

  • TENS acupuncture: effective, but its application is indicated for short periods.

  • TENS Burst: This mode is a mixture of conventional and acupuncture modes. It transmits a basic low-frequency current. For these four types, the following table gives us idea about these modes [18].

4.2 The developed PWM-TENS strategy

The proposed PWM-TENS technique is illustrated in Fig. 7. It uses a variable frequency oscillator (from 2 to 150 Hz) which the output is modulated with the current intensity by using the PWM technique, well known in electronics and telecommunications. The oscillator was controlled by the stimulation rate. The obtained output signal is a train of pulses with variable widths and frequencies (Fig. 8). Thus the obtained signal is optimized according to three parameters of stimulation (frequency, current, pulse width). This modulated method is very interesting because it reduces the energy and current demands, enhance the sensation during treatment and stimulation periods and can be repeated for the same day in order to obtain better results.
Fig. 7

Gate. The PWM-TENS principle

Fig. 8

Gate. The PWM-TENS output signal

The spectral analysis of the spikes stimuli of Fig. 9, demonstrates that the spectrum contains several harmonics which can disturb the nerve stimulation configuration and parameterization. In fact, the stimulus x(t) can be expressed as:
$${\text{x}}({\text{t}}) = {\text{a}}.{\text{E}}.[1 + 2\sin {\text{c}}({\text{a}}).\cos (2.\uppi.{\text{f}}.{\text{t}}) + \ldots 2\sin {\text{c}}({\text{n}}.{\text{a}}).\cos (2{\text{n}}\uppi.{\text{f}}.{\text{t}})]$$
(1)
where E, signal amplitude; a, spike width; T, stimuli period; n, harmonic rank.
Fig. 9

Spectral analysis of a spike stimulus

4.3 Electro stimulation programs

Five programs of stimulation are designed and simulated. The first one (program 1 of Table 3) is a conventional TENS program where the frequency is set to 80 Hz and the pulse width is fixed at 180 μs: This mode is recommended for the treatment of acute and chronic pain, nociceptive or neurogenic origin. This electrical stimulation of A-beta fiber exerts inhibition of pathways for transmission of pain.

In the program 2, the frequency is 2 Hz and is modulated with a carrier of 80 Hz, the pulse width is fixed to 180 μs. This mode called TENS-Burst is generally most effective for the treatment of referred pain in the arms and legs when the touch sensitivity threshold of the patient is lowered or changed in the event of severe muscle pain or when the post effect of the high frequency stimulation is too short. The analgesic effect obtained by low frequency TENS burst is generated by a muscle stimulation causing the release of specific components to the body and similar to morphine, endorphins.

Program 3: is called mixed frequency (3 s at 2 Hz and 3 s at 80 Hz). The stimulation varies alternatively every three seconds between the different frequencies. This type of stimulation which incorporate low and high frequencies, allows in some cases more effective treatment.

Program 4: This program is intended for facial treatment; it has biphasic pulses with a width less than other programs. A smaller pulse width is sensitive and highly innervated areas such as the human face. A short pulse width authorizes an increase of the amplitude, allowing best results and treatments: the patient does not feel pain; the frequency is set to 80 Hz and the pulse width 60 μs.

Program 5: is designed for the treatment of nausea. Frequency is set to 10 Hz with a pulse width of 180 μs.

4.4 Simulations

We have simulated under Matlab software the different modes in order to verify its performances. In Figs. 10 and 11, we illustrated the stimuli waveforms, its spectrum and spectrograms. For example, in Fig. 10, we can observe the modulated width of the stimuli spikes corresponding to a variable TENS current. The spectrum shows that the maximal energy is located at 25 Hz for this kind of stimulation. However, according to Fig. 11 related to gate control stimulation, the optimal frequency of stimulation is showed by the spectrum and spectrum and is around 18 and 26 Hz. Nevertheless, all figures demonstrate that the optimal frequency domain of nerve stimulation is between 1 and 50 Hz.
Fig. 10

Spectral analysis of the PWM-TENS Stimuli: waveform, spectrum, spectrogram and autocorrelation

Fig. 11

Spectral analysis of the gate control stimuli: waveform, spectrum, spectrogram and autocorrelation

5 Design and implementation of the electro-stimulator

The electronic conception is based on the TENS model especially CEFAR PRIMO PRO. For this, we propose to generate specific stimulation signals thanks to an embedded platform developed under the famous Arduino board which offers high flexibility in the choice and programming of the signal parameters and shapes. Our stimulator consists of a pulse generator (Arduino), a battery charger, an amplifier stage and isolation and an output stage. Figure 12 presents its block diagram.
Fig. 12

Block diagram of the electric stimulator

The programming of the TENS stimulator is illustrated by the algorithm of Fig. 13 with C language. At first, the user must fix the therapeutic mode which is suitable to his pain and disease. This choice corresponds to programs 1–5 pre-programmed in the Arduino processor. At the second stage, the patient should select the parameters of stimuli such as current amplitude, frequency and pulses width according to his feeling and sensation of pain. After validation, the stimuli signals are applied to electrodes which are placed on the patient skin. Finally, the five programs offers to the user to choice the period of therapy (in min or h) after activating the selected electrodes and parameters selection.
Fig. 13

TENS stimulation implementation algorithm

Figures 14 and 15 give an illustration of the experimental output stimuli respectively for the TENS-Burst mode and the conventional mode.
Fig. 14

Experimental output stimuli for the mode 2: TENS-Burst

Fig. 15

Experimental output stimuli for the mode 1: conventional

6 Discussion

We had seen that TENS applies stimulation across a range of frequencies and may help to prevent the development of tolerance to the electrical stimulation [19]. Intensity appears to be a critical factor in optimizing TENS efficacy and it is thought that regardless of frequency of application, the intensity needs to produce a strong, non-painful sensation which ideally is titrated during treatment to maintain the intensity level. Placement of electrodes may also influence the response nerves and modifies the stimuli results.

Our comparative study conducted in the previous paragraph between existing strategies TENS showed that the simulation results applied on Peripheral nerve stimulation (PNS) and spinal cord stimulation (SCS) demonstrate that the C-TENS or Conventional Gate Control using high frequency stimulation and low current intensity causes non-painful paresthesias in local areas, but this effect does not persist after stopping the stimulation process. The AL-TENS method (“Acupuncture Like” or “Burst”) which combines low frequencies waves and high current intensities is responsible for weak twitching and provide rapid analgesia which increases during stimulation and persists after the treatment mechanism.

These results confirm that high intensity and stimuli with varying frequency can give the best prolonged therapeutic results. However, for most actual equipments available on the market, the current rise is limited by the RF frequency range and the width of the pulse as it produces a painful sensation for the patient during the stimulation period. The proposed PWM-ENS technique solve this problem by varying the pulses widths and the stimulation frequency by a PWM technique in which the current intensity is considered as the modulator signal and the stimulation rate as the HF currier frequency. The signal obtained is optimized according to three parameters of stimulation (frequency, current, pulse width).

7 Evaluation

We tested our technique on a population consisting of 15 patients aged between 40 and 62 years, with: non-cancer pain, peripheral neuropathic, osteoarthritis, traumatic facial pain and head. Figure 16 gives an illustration of the EVA evaluation score estimated by every patient after 12 days of PWM-TENS stimulation. The results of Figs. 16 and 17 show that the pain sensation is reduced from 80 to 40% after 15 days and 20% after 1 month of treatment. It seems that for high values of pains (> 80), the pain reduction is less efficient and requires placebo or associated pharmacology drugs and treatment.
Fig. 16

EVA evaluation score after the first 12 days of PWM-TENS stimulation

Fig. 17

EVA evaluation score of patient no. 3 during 30 days of PWM-TENS stimulation

The following section describes protocols and results.

7.1 Protocol

We divided the patient sample into two groups: one is placebo controlled and the other is PWM-TENS.
  • 9 patients were satisfied after 12 days of treatment, They continue to be followed without changing randomization

  • 6 patients who have not noticed improvements but they continue to follow the session’s stimulation.

7.2 Criteria for administration of electro-stimulation

  • exclusion for children under 10 years

  • Patients with other diseases or receiving treatments that can resound on bone metabolism or

  • Patient with malignant disease or any disease that can reduce their life expectancy

  • no stimulation during sleep,

  • Never drive into the heart area

  • Do not use during pregnancy or breastfeeding

  • Do not use on irritated skin area or on a burn,

  • Do not apply to the anterior cervical, thoracic, carotid sinus, abdomen during pregnancy.

7.3 Evaluation criteria and methods to measure pain

  • EVA: pain intensity assessed by visual analog scale, rated from 0 to 10, the most painful site.

  • the number of painful sites

  • consumption of analgesics,

  • quality of life scales and the resumption of normal life

  • radiological improvement, evaluated qualitatively on osteolytic areas and/or thickening of the cortical. The test will be judged by two independent radiologists, trained and specialized in musculoskeletal radiology.

  • primary endpoint: number of satisfied patients of treatment and number of patients willing to continue treatment;

  • the date of the discontinuation of dissatisfaction: Kaplan–Meier curve.

7.4 Results

  • Primary endpoint: after the first 2–3 days: no significant difference between the two groups (Placebo and PWM-TENS).

  • After 1 month: 62% satisfaction in the TENS group against 53% in the Placebo.

  • With the PWM-TENS group, improvements can be achieved in 3–5 days, it remains significant throughout the 15 days of post treatment follow.

  • The EVA score for pain fall into two groups of an average of 60–30 when patients prolonged treatment.

  • This study also shows the medium term (2–3 months) of patients with chronic pain is also satisfied with the TENS.

  • Both procedures (placebo) and PWM-TENS also have a close effect on the reduction of pain (> 50%).

The comparison of our obtained metrics with classical TENS results demonstrated that we succeeded to:
  • reduce the period of stimulation and physical treatment

  • Reduce the pain index EVA from 80 to 35 contrarily to classical TENS which reduces the same cases from 80 to 50 as illustrated in Table 4.
    Table 4

    Comparison results between classical TENS and PWM-TENS

    Tested population

    Initial pain metric EVA

    Pain metric before stimulation EVA1

    Pain metric after stimulation EVA2

    Treatment period in days

    15 patient age: 40–62

    50–80

       

    Traditional TENS

    50–80

    80

    50

    7–30

     

    70

    43

     
     

    60

    38

     
     

    50

    35

     

    Modified PWM-TENS

    50–80

    80

    35

    5–12

     

    70

    30

     
     

    60

    25

     
     

    50

    20

     
These results proved that:
  • For Acute pain

High frequency TENS stimulation offers the best results and pain reduction but its benefit is limited as a standalone treatment for severe to moderate pain. In this case, the stimulation procedure may be combined with a pharmacotherapy. This result is confirmed by references [20, 21] which suggest that TENS is beneficial for acute orofacial pain, painful dental procedures, fractured ribs, acute lower back pain.
  • For Chronic pain

TENS stimuli seems to be beneficial for localized muscle pain, post-herpetic neuralgia, trigeminal neuralgia, phantom Limb, stump pain, diabetic neuropathies and entrapment neuropathies, radiculopathies (cervical, thoracic and lumbar), complex regional pain syndromes type I (reflex sympathetic dystrophy) and type II (causalgia). TENS may also be beneficial for cancer related pain, rheumatoid arthritis of the hand, whiplash and mechanical neck disorders, post stroke shoulder pain and chronic recurrent headache are inconclusive [22].

7.5 Main innovations

  • Innovation and added value of this study is to provide a medical tool that allows objective evaluations for short and medium periods of pain treatments. We integrated in the algorithm of PWM TENS several dynamic evaluation metrics thanks to the patient interactivity and evaluation. This tool will assist the doctor (according to physiological data acquisition stored on the device) to evaluate and follow the therapy and physical treatment.

  • Currently, the evaluation of TENS results are subjectively established by clinical observation and not in a real time mode. However, our method is based on an embedded time record on the device memory of the stimulator throughout the day and along the evaluation period (7, 15 days, 1, 2, 3, 6 months, 1 year). All the evaluation parameters are programmed and displayed for better monitoring, following and interpretation of the progress of the disease and its therapy.

  • We solved the problem of residual current in the brain. Indeed, previous studies on electrostimulation, noted that TENS currents inhibit the nervous system from healing, and increases the sympathetic stress on the body. In fact, we demonstrated that, biophysically, it is not the current itself that could hinder the nervous system but the electric load (q) that leaves it in the body. We found in the paper the solution by canceling the average value of this electric load by alternately generating positive and negative pulses with same amplitudes so they compensate themselves to obtain a null average current.

8 Conclusion

This paper presents a study of an electronic conception of a transcutaneous electrical nerve stimulator designed for reducing acute and chronic pains. The principle is based on the new TENS-PWM strategy which generates modulated asymmetric biphasic signals dedicated to simulate the nerves that control pains. The electrical pulses are transmitted by flexible electrodes placed on the skin and into a body surface location of the nerve.

Its operating principle is to produce a higher rate of substance secreted by the brain. The simulation results applied on Peripheral nerve stimulation (PNS) and spinal cord stimulation (SCS) demonstrate that the C-TENS or Conventional Gate Control using high frequency stimulation and low current intensity causes non-painful paresthesias in local areas, but this effect does not persist after stopping the stimulation process. The AL-TENS method (“Acupuncture Like” or “Burst”) which combines low frequencies waves and high current intensities is responsible for weak twitching and provide rapid analgesia which increases during stimulation and persists after the treatment mechanism. Finally, we succeeded to implement and realize this Electric stimulator on an embedded Arduino card as a portable device. Its advantage is the modularity and the simplicity of configuration and optimizing the stimuli modes with their parameters. Our contribution was the integration in this device of a new PWM-TENS strategy which allows us to increase the current intensity even with high frequencies without any sensation of pain. Moreover, everyone can easily use it at home for a long term. Finally, we can conclude that Electrotherapy is typically used in conjunction with other treatments, rather than by itself. For people undergoing physical therapy, electrotherapy may alleviate pain sufficiently for an individual to participate more actively in targeted exercises.

In conclusion, our modulated stimulation strategy benefits from a much more adaptive and innovative technology. It allows reaching deeper areas thanks to a modulated wave, while ensuring the patient wears pleasant. In order to enhance the medical following and evaluation of the stimulation strategy and results, we have inserted a real time embedded algorithm with the electronic stimulator. This numerical tool computes and stores and subjective objective stimulation parameters and metrics. The experiments and tests on several patients demonstrated satisfactory results, especially after 5 days of the beginning of the stimulation phases. As a perspective of this work, we are considering extending our study and our trials of this technique of nerve stimulation (TENS) to treat depression and anxiety.

Notes

Acknowledgements

This work is conduct with the cooperation of the National Institute of Biomedical Studies of Tunis.

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© Springer Science+Business Media, LLC, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Electric Engineering DepartmentNational High Institute of Biomedical Studies of TunisTunisTunisia
  2. 2.Image and Signal Processing LaboratoryUniversity of Tunis ManarTunisTunisia

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