(1,2)Al-Nahrain University-College of Engineering, Iraq-Baghdad, (3)Ministry of Health- Public Health Directorate, Iraq-Baghdad
Abstract
The present study aims to give a solution to help relieve pain through electro-analgesia by the design and implementation of a Transcutaneous Electrical Nerve Stimulation (TENS) unit which is the electrotherapeutical process of using electrical current to excite and stimulate the nervous system of a living body. In the present study, an electrical unit that consists of multiple modules is designed and implemented. These modules are: a pulse generation module, which generates continues, asymmetric biphasic signals using the NE555 oscillators, a timing module that controls therapy time using a microcontroller and a relay, a skin-electrode interface module that provides the appropriate method to deliver the generated signal to the subject’s skin using surface electrodes and a unit case, which was designed using DesignSpark Mechanical 2.0 software. The designed unit provides the user with the ability to control signal parameters (frequency, pulse width and voltage intensity) and therapy time and modulate them so that an optimum effect is achieved for the purpose of pain management. Tests had been made on 12 cases with various conditions of pain intensity represented by acute and chronic pain, which took place inside health care facilities and under physician supervision. The proposed unit provides a frequency range of (2-119) Hz, a stimulation intensity of up to 111 V, a pulse width of (50-210) µs and a session time of (1-30) min. which is sufficient for many patients. The results demonstrated that the intensity of stimulation has the most significance in the process of pain relief and it varies according to the condition of each patient, the range of the in intensity for the tested cases was (50-77) V, which is also directly proportional to the severity of pain. Higher intensities of pain required higher intensities of stimulation and vice versa.
The pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage. It has a location; duration, intensity and distinctive quality. It is a major symptom in many medical conditions, significantly interfering with a person’s quality of life and general functioning. It is also one of the most challenging health problems facing many people around the world and it is our role as biomedical engineers to help provide solutions to these problems [1].
Many methods were developed throughout the years to help cure pain. One of these methods is pharmacological which includes the use of drugs such as Aspirin and Morphine to relief pain. The other method is non-pharmacological, where pain control can be done through exercise which may help decrease inflammation, increase mobility, and decrease overall pain levels [2].
Another non-pharmacological way of treating pain is through electroanalgesia. This includes: Percutaneous Electrical Nerve Stimulation (PENS); Electrical Muscle Stimulation (EMS) and Transcutaneous Electrical Nerve Stimulation (TENS) which is the subject of the present study. During TENS, pulsed currents are generated by a portable pulse generator and delivered across the intact surface of the skin via conducting pads called “electrodes” which will then stimulate the nerves and suppress the pain. Transcutaneous electrical nerve stimulation (TENS) is a simple and non-invasive analgesic technique that is used extensively in health-care settings by physiotherapists, nurses and midwives [3]. It can be administered in the clinic by health-care professionals or at home by patients who have purchased a TENS device directly from manufacturers. People use this tool to mitigate pain for numerous diverse types of illnesses and conditions. They use it most often to treat muscle, joint, or bone problems that occur with illnesses such as: osteoarthritis or fibromyalgia, or for conditions such as low back pain and neck pain [4]. People also use this machine to treat Sudden (acute) pain, such as birth pain and long-lasting (chronic) pain, such as cancer pain [5].
The TENS can provide the patient with a safe and effective method of achieving pain relief with no side effects. Complications of TENs are rare and consist mainly of skin irritation due to the electrodes which should resolve with discontinuation of treatment. The benefits of TENS can include a reduction in analgesic intake, improvement in sleep pattern, increased activity and a feeling of control over the pain. The patient’s sense of control over their pain promotes a self-management approach to the pain problem [6].
The type of stimulation delivered by the TENS unit aims to excite (stimulate) the sensory nerves, and by so doing, activate specific natural pain relief mechanisms. For convenience, if one considers that there are two primary pain
relief mechanisms that can be activated: the Pain Gate Mechanism and the Endogenous Opioid System [7] Under normal physiological circumstances, the brain generates pain sensations by processing incoming noxious information arising from stimuli such as tissue damage. In order for noxious information to reach the brain, it must pass through a metaphorical ‘pain gate’ located in lower levels of the central nervous system. In physiological terms, the gate is formed by excitatory and inhibitory synapses regulating the flow of neural information through the central nervous system. This ‘pain gate’ is opened by noxious events in the periphery. The pain gate can be closed by activation of mechanoreceptors through ‘rubbing the skin’. This generates activity in large diameter Aβ afferents, which inhibits the onward transmission of noxious information. This closing of the ‘pain gate’ results in less noxious information reaching the brain reducing the sensation of pain as shown in Figure 1
Figure (1): The Pain Gate Mechanism[8].
The neuronal circuitry involved is segmental in its organization. The aim of conventional TENS is to activate Aβ fibres using electrical currents. The pain gate can also be closed by the activation of pain-inhibitory pathways that originate in the brain and descend to the spinal cord through the brainstem (extrasegmental circuitry).
These pathways become active during psychological activities such as motivation and when small diameter peripheral fibres (Aδ) are excited physiologically. The aim of AL-TENS is to excite small diameter peripheral fibres to activate the descending pain-inhibitory pathways. Pain relief by means of the pain gate mechanism involves activation (excitation) of the A beta (Aβ) sensory fibres, and by doing so, reduces the transmission of the noxious stimulus from the ‘c’ fibres, through the spinal cord and hence on to the higher centres. The Aβ fibres appear to appreciate being stimulated at a relatively high frequency HF (in the order of 90 - 130 Hz or pps). It is difficult to find support for the concept that there is a single frequency that works best for every patient, but this range appears to cover the majority of individuals. Clinically it is important to enable the patient to find their optimal treatment frequency – which will almost certainly vary between individuals. An alternative approach is to stimulate the A-delta (Aδ) fibres which respond preferentially to a much low frequency LF (in the order of 2 - 5 Hz), which will activate the opioid mechanisms, and provide pain relief by causing the release of an endogenous opiate (encephalin) in the spinal cord which will reduce the activation of the noxious sensory pathways. In a similar way to the pain gate physiology, it is unlikely that there is a single frequency in this range that works best for everybody. Patients should be encouraged to explore the options where possible.
The goal of the study was to construct an integrated system, which encompasses different modules including: the pulse generation, timing, skin-electrode interface and the case design of the unit. Each one of these modules is either constructed from hardware parts, software programs or both and provides a unique function that contributes to the process of pain control. The methodological flow-chart for the operation of the designed unit is shown in Figure 2.
The timing module was designed to provide a session timing in the range of 1-30 minutes. Therapy time can be adjusted by a potentiometer to achieve the safety condition mentioned above and to provide the patient with an efficient range of therapy time and thus more comfort while using the device. Figure 3 illustrates the circuit design of the timing module.
The timing module consists of:
• Microcontroller (Arduino UNO R3).
• Relay (SRD-05VDC-SL-C).
• Push buttons.
• Battery
• Potentiometer (1 KΩ).
• LED
This unit controls therapy time by switching the battery that supplies the pulse generation module on and off correspondingly. A code is constructed via Arduino software. After uploading the code to the Arduino, the timing module is ready to function. First, the potentiometer’s value is adjusted by the user to give a corresponding time of therapy, where any value between 1 and 30 minutes can be selected.
After settling on the desired time for the patient, the ON button is pressed and the LED turns on to indicate that the device is functioning and the battery delivers current to the pulse generation unit.
This module is responsible for generating continuous, asymmetrical biphasic pulses that are responsible for the pain relief mechanism. The first stage of the circuit design of this module as shown in Figure (3.8) is the supply source which is a Li-ion rechargeable battery that delivers 2200 mA (11.1 V) of current, which is sufficient to power all components. The ICs are used in the circuit function as oscillators that generate pulses which are modulated via potentiometers. R3 potentiometer is responsible for modulating frequency, R2 potentiometer is responsible for modulating the pulse width and R1 potentiometer is responsible for modulating the intensity of stimulation. An IRF9640 MOSFET is used to drive the output which is connected to the low impedance winding of the output transformer and the larger winding is connected to the probes and ground.
This circuit also consists of a combination of capacitors for the noise cancelling and one capacitor particularly set to define the output frequency coupled up with the variable resistor or the potentiometer R3. The implementation of this circuit is shown in Figure 4.
The connection between the device and the patient's skin takes place at the skin-electrode interface module. This connection is established using self-adhesive surface electrodes that are attached to the pain site over the patient's body as shown in Figure 5.
The software portion of the propose system includes the programming of the microcontroller- based board for the timing module and the DesignSpark Mechanical 2.0 software which was used to design the case of the proposed system.
The Arduino IDE (interactive development environment) software is the software program of the Arduino UNO which was downloaded from www.arduino.cc/en/main/software. The code utilized to develop the timing module of the proposed system is illustrated in Figure 6.
Figure 6: Timing Module Code Displayed on Arduino IDE Window.
DesignSpark Mechanical is a free 3D CAD (computer-aided design) solid modelling software. This software was utilized to design the case of the proposed system. The case design consists of two parts: the top and the bottom. The top part of the case has openings to implement potentiometers, push buttons and the LED with dimensions corresponding to the dimensions of the employed components. On the sides, the openings for the USB port and the DC input port of the Arduino UNO are located. Another opening is located on the side through which the electrode wires passage as shown in Figure 7.
Figure 7: Component Locations on Case Top.
The bottom part of the case has two compartments: the first is where the Arduino UNO (timing module) is located and the second is where the pulse generating circuit is located as shown in Figure 8.
The result of the study is divided into three separate parts, which are the results of the timing module that include the resulted therapy time, the results of the pulse generation module, which includes the generated signal, and lastly, the results obtained from study cases.
The proposed design of the timing module resulted in a therapy time in the range of 1 to 30 minutes, which is the advised therapy time for the TENS unit. The time range can be viewed on the serial monitor of the Arduino IDE. The potentiometer has an analogue range of 0 to 1KΩ which corresponds to 0 to 1024 bits digitally. This range is mapped to 0 to 30 minutes. Figure 11 illustrates a therapy time of: A-15 min. and B- 30 min. which corresponds to a value of 1KΩ of the potentiometer thus the submitted code converted the potentiometer value to the corresponding therapy time digitally.
Figure 11: Therapy Time Displayed on Serial Monitor Window in Arduino IDE. A-15 min., B-30 min.
The pulse generation module produced continuous, asymmetric biphasic signals. The following segments demonstrate the generated signals pre and post transformer stage, illustrating its features and parameters.
The acquired signals yield a satisfactory operation of the designed unit. The parameters of the acquired signal up to this stage were as illustrated in Table 1.
The acquired signal post-transformation is similar to the signal illustrated in the pre-transformer stage in terms of wave parameters and shape with the exception of pulse intensity. The acquired voltage intensity in this stage is 111 V, which is 10 times higher than the intensity of the previous stage and is a functional pulse intensity for the pain relief purpose as shown in Figure 12. The x-axis represents time with a scale of 50 µs/division and the y-axis represents sensitivity with a scale of 50 V/division.
A pain relief model of electrical stimulation was tested on patients of varying age groups and conditions. This segment illustrates the efficiency of the TENS unit to relieve pain and the functional pulse intensities which yielded a satisfactory result for those patients [9, 10].
Table 2: Study Cases.
From the results above, pain is classified into low, moderate and high based on its intensity. Pain can be measured based on the numerical rating scale (NRS), which requires the patients to rate their pain on a defined scale. For example, 0–10, where 0 is no pain and 10, is the worst pain imaginable [11]. In the present study, 3 cases diagnosed with low pain intensity (NRS=3) were examined as shown in Figure 13 , where the x-axis represents the numerical rating scale (NRS) with a scale of 0.5 NRS value/division and the y-axis represents the voltage intensity of stimulation in volts with a scale of 0.5 V/division.
Figure 13: NRS for Low Intensity of Pain.
In the present study, 4 cases with moderate pain intensity (NRS=5) were examined as shown in Figure 14, where the x-axis represents the numerical rating scale (NRS) with a scale of 1 NRS value/division and the y-axis y-represents the voltage intensity of stimulation in volts with a scale of 2.
Figure 14: NRS for Moderate Intensity of Pain.
Finally, 5 cases with high pain intensity (NRS=7) were examined as shown in Figure 15, where the x-axis represents the numerical rating scale (NRS) with a scale of 1 NRS value/division and the y-axis y-represents the voltage intensity of stimulation in volts with a scale of 1 V/division.
Pain relief via electrical stimulation was tested on twelve cases of varying age groups and medical conditions. The patients were organized in 3 groups based on their pain intensities, which were low, moderate and high. It was noticed that for moderate and low intensities of pain, low intensity of stimulation resulted in curing the pain completely while higher intensities of pain required higher intensities of stimulation and the pain was partially relieved. The stimulation was applied five times a week at an interval of 24 hours.
From the results above, it is observed that the intensity of stimulation is directly proportional to the intensity of the pain. It was observed that the optimal dose, including the number, duration, and frequency of treatments were not uniform.
Several factors affect the efficiency of the TENS unit. These factors include:
*The severity of pain of The patient.
*Tolerance: patients who are using The TENS unit on daily at The same frequency and intensity can develop a Tolerance to The treatment. This explains The stimulation schedule that is introduced in The present which eliminates The possibility of developing Tolerance to The stimulation.
* Stimulation intensity.
* Stimulation frequency.
* Electrode placement.
* Interactions with pharmacological agents: low-frequency TENS was ineffective when opioid tolerance was present.
It is believed that electrical stimulation is a safe, simple and reusable method of pain relief involving the use of low electrical current. When the machine is switched on, small electrical impulses are delivered to the affected area of the body using the electrodes, which is felt as a tingling sensation. The electrical impulses can reduce the pain signals going to the spinal cord and brain, which may help relieve pain and relax muscles. Based on the work done in the present study, the proposed TENS unit is characterized by the following:
* It is a non-invasive system because of the choice of an appropriate type of surface electrodes, which makes it easier to be self-administered by the patients to manage their painful conditions.
* It provides a low cost system for controlling pain as opposed to pharmacological drugs, which can cost a lot of money, especially if needed for long periods of time.
* It is small and compact in size, which provides the patients with more comfort when using the unit.
* Regular use of the unit results in the following positive results: reduced irritability, stress and anxiety reduction, easier physical movement, decreased use of pain relief drugs, improved attitude and social life, and fewer trips to the doctor.
* It is safe and has no side effect as opposed to pain relieving drugs, which may cause side effects like nausea, vomiting or drowsiness.
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