Low Frequency TENS (PDF)

**[Transcutaneous Electrical Nerve Stimulation]** **[(TENS)]** [**Definition**:] **Transcutaneous :** Means through intact skin so TENS is noninvasive method of electrical stimulation through intact skin primarily aiming to provide a pain relief. Generally, waveforms of TENS are biphasic and can...

**[Transcutaneous Electrical Nerve Stimulation]** **[(TENS)]** [**Definition**:] **Transcutaneous :** Means through intact skin so TENS is noninvasive method of electrical stimulation through intact skin primarily aiming to provide a pain relief. Generally, waveforms of TENS are biphasic and can be categorized into various waveforms as spike waves, square, rectangular or sine waves. Spike waves are more irritating to the skin; so they required frequent movement of electrodes or shorter treatment time, they are recommended for intense or hyper-irritating stimulation such as acute pain. While square, rectangular or sine waves are longer duration waveforms; with which the skin irritation is less. **Fig. (1)** C:\\Users\\Marwa Taher\\Pictures\\Saved Pictures\\TENS waveforms.jpg **Fig.1: Waveforms of TENS** In practice; it is the cathode that excites the axons, so the cathode is placed proximal to the anode to prevent the blockage of nerve transmission due to hyper polarization. (Fig. 2)  ***Fig. 2: Electrodes Arrangement*** ***[Types of TENS:]*** [**1. Conventional TENS (high frequency, low intensity) or high TENS**:] The aim of conventional TENS is to activate selectively large diameter Aβ fibers without concurrently activating small diameter Aδ and C (pain related) fibers or muscle efferent, It is characterized by short phase duration (60 - 100 µsec), high pulse frequency (90 to 130 Hz or pps) with a sensory-level output which activates spinal gate (Gate Control Theory) causing long-term treatment. It is effective in treatment of acute pain. (Fig.3 a&b) C:\\Users\\Marwa Taher\\Pictures\\Saved Pictures\\TENS & A beta.jpg **Fig.3a&b: Activation of A beta fibers by high TENS** **[2. Burst Mode TENS (high frequency. very long pulse):]** It is conventional TENS but delivered in burst mode. It is characterized by long phase duration (300 to 1000 µsec); high pulse frequency (\> 100 pps) and a pulse rate (2-3 bursts/sec). (Fig.4) **Fig.4: Burst mode TENS** **[3. Acupuncture Like TENS (low frequency, high intensity) or Low TENS:]** The aim of low TENS is to selectively activate the group I efferent producing muscle contraction which result in stimulation of ergo-receptors and group III afferent. It is characterized by long phase duration (200 to 250 µsec), low pulse frequency (2 to 4 Hz) with a motor-level output (twitch ms. contraction). It causes the release of B-endorphin which binds to the A-delta and C fiber receptor sites to block the transmission of pain. It is effective in treatment of chronic pain. (Fig.5 a &b)  **Fig.(5a&b) : Stimulation by Acupuncture or Low TENS** **[4. Brief Intense TENS:]** The aim of intense TENS is to activate small diameter Aδ (A delta) cutaneous afferents by delivering TENS over peripheral nerves arising from the site of pain at an intensity which is just tolerable to the patient. It has a frequency (100- 150Hz), phase duration (150-250µsec) and short treatment duration (less than 15 min)\' It is best used for intense pain (e.g. post surgical). (Fig. 6) C:\\Users\\Marwa Taher\\Pictures\\Saved Pictures\\TENS & peripheral mechanism.png **Fig. 6: Peripheral mechanism of pain relief by TENS** Recently, new features are added to the TENS devices such as modulated frequency, modulated amplitude, and modulated duration. (Fig. 7a&b)  **Fig.7a&b: TENS modulations** **[Physiological effects of TENS:]** The main physiologic effect of TENS is pain relief through: 1\. Gate control theory (modulated by High TENS) 2\. Endogenous-Opioid mechanism (modulated by Acupuncture-like TENS) 3\. Peripheral mechanism (modulated by intense TENS) **[Therapeutic uses of TENS:]** l\. Control of acute or chronic pain 2\. Management of post-surgical pain 3\. Acute or chronic myofascial pain. 4\. Reduction of post-traumatic acute pain 5\. Acute or chronic pain of musculoskeletal disorders and soft tissue injuries (e.g. LBP, arthritis) 6\. Neurologic pain (e.g. trigeminal neuralgia) **[Recent uses of TENS:]** 1. Muscle strength 2. Improve cutaneous blood flow 3. Wound healing 4. Fracture healing (non-united fracture) **[Contraindications for the use of TENS:]** -Stimulation of the abdominal, lumber and pelvic region during pregnancy -Over the carotid sinus - Pacemaker -Cancer -Deep venous thrombosis -Metal implant **[Complications:]** 1\. Skin irritation due to electrolyte or long sensation 2\. Neurotic addiction to stimulation. **[Advantages of TENS]**: 1\. Non-invasive 2\. Easy to operate and apply 3\. Has few side effects 4\. Patients can administer by themselves 5\. Cheap. **[Medium frequency currents]** Medium frequency currents are alternating currents with a frequency in the kilohertz range, and often referred to as kilohertz frequency alternating currents. The most popular current in this range is interferential current and Russian current. Nowadays more currents have been introduced as Aussie current. - ***Interferential current*** - ***Russian current, Aussie current*** **[Interferential current (IFC) ]** **[Introduction]** The original concept of interferential therapy was developed by Austrian physician Dr. Hans Nemec , who proposed that the crossing of two slightly different medium frequency alternating currents within the tissue, will create a third frequency current of greater intensity in the deeper tissue. **[Definition:]** - The transcutaneous application of alternating medium-frequency electrical currents, amplitude modulated at low frequency for therapeutic purposes. - IFC is derived from the interference of two symmetrical but asynchronous, kilohertz frequency, sinusoidal alternating currents resulting in a single treatment, or interference, current with properties uniquely different than the original input currents. - In other words interferential therapy utilizes two medium frequency currents which pass through the tissues simultaneously. They are set up so that their paths cross; and in simple terms they interfere with each other. This interference gives rise to an interference or beat frequency, which has the characteristics of low- frequency stimulation. (Fig. 8) C:\\Users\\Marwa Taher\\Pictures\\Saved Pictures\\interferential 1.png **Fig.8: Generation of amplitude modulated interference wave** ***[Production of interferential current:]*** - When two asynchronous kilohertz frequency (1 to 10 KHz) sinusoidal currents are directed to intersect or interfere, the waves are periodically in synch or in phase with each other, and the amplitudes of the two currents will sum together. This is termed **constructive interference**. - Equally periodic, the currents will be out of phase, resulting in **destructive interference**, and the amplitudes will negate each other. As the two currents go in and out of synch, the amplitude of the interference current gradually increases and decreases. Because of the modulation of amplitude, IFC is referred to as **amplitude modulated AC**. (Fig.9)  **Fig.9: Interference of two currents to form IF** - IFC is produced by mixing two medium-frequency currents that are slightly out of phase, either by applying them so that they \'interfere\' within tissues **(Quadripolar)** , or alternatively by mixing them within the stimulator prior to application **(Premodulated or bipolar**). (Fig.10) C:\\Users\\Marwa Taher\\Pictures\\Saved Pictures\\interferential 4.png **Fig.10: Bipolar & Quadripolar techniques** - One current is normally of fixed frequency, for example at 4000 Hz, and the other current is adjustable, for example between 4000 and 4200 Hz. [**Principle of interferential therapy**:] - The basic principle of the interferential therapy (IF) is to utilize the strong physiological effects of the low frequency electrical stimulation of muscle and nerve tissues at sufficient depth, without the associated painful and somewhat unpleasant side effects of such stimulation. The medium frequency currents penetrate the tissues with very little resistance, whereas the resulting interference current (low frequency) is in the range that allows effective stimulation of the biological tissues. The resistance (impedance) of the skin is inversely proportional to the frequency of the stimulating current. - In other words, the lower the stimulation frequency, the greater the resistance to the passage of the current, so more discomfort is experienced. The skin impedance at 50 Hz is approximately 3200 ohms, whilst at 4000 Hz it is reduced to approximately 40 ohms. The result of applying this latter frequency is that it will pass more easily through the skin, requiring less electrical energy input to the deeper tissues, giving rise to less discomfort.  **[The pattern of the interferential area may be static or dynamic:]** ***Static interference:*** - The area in which the produced interferential current remains stationary. This area of static interference gives an appearance of clove leaf as a result of the vector addition of two currents and it lies to 45º angles to the perpendicular lines from each electrode. (Fig.11) C:\\Users\\Marwa Taher\\Pictures\\Saved Pictures\\interfer 6.jpg **Fig.11: Static interference** ***Dynamic Interference***: - The area in which interference current is developed is moving in a to and fro manner through 45\". It is obtained by varying the current intensity in suitable manner. Current is varied from 50 to100%. This dynamic area of interference is also called as vector sweep, vector scan. It can also be rotated through 90º. (Fig.12)  C:\\Users\\Marwa Taher\\Pictures\\Saved Pictures\\interfer 5.png **Fig.12: Dynamic interference** **[Physiological and Therapeutic Effects of IFC:]** The current flowing between each pair of electrodes is insufficient to stimulate nerve and muscle directly until amplitude is modulated by interference. Interferential therapy thus reduces the stimulation of cutaneous sensory nerves near the electrodes whilst promoting the effect upon deep tissues. **The physiological effects depend on the factors such as the:** 1. Magnitude of the current. 2. Mode (constant/ sweep). 3. Frequency used. 4. The accuracy with which the electrodes are placed. 5. The pathological condition. **[The common effects produced are:]** ***1-Pain relief:*** The interferential current is used in management of acute and chronic pain of different origins, especially post traumatic pain and sympathetically-maintained pain as in shoulder hand syndrome and Raynaud\'s disease (spasm of the digital arteries producing pallor or cyanosis of fingers or toes). ***Mechanisms of pain control by interferential therapy:*** - Stimulation with the higher frequencies of about 100 Hz at the sensory level intensities stimulates pain gate mechanisms, thereby mask the pain symptoms. - Stimulation with lower frequencies up to 10 Hz at motor level intensities can be used to activate the Opioid mechanism, providing a degree of relief. - Decreased activity of the sympathetic ganglion and sympathetic nerves in cases of sympathetically-maintained pain. ***2-Motor stimulation:*** - Stimulation of the motor nerves to induce contraction of muscle can be achieved with a wide range of frequencies (10 -50 Hz). Clearly, stimulation at low frequency (1 - 10 Hz) will result in a series of twitches, whilst stimulation at 50 Hz will result in a tetanic contraction. The choice of treatment parameters will depend on the desired effect. - **If IF is used as neuromuscular stimulation, it can be used for**: a. Relaxation of muscle spasm. b. Prevention and retardation of disuse atrophy. c. Muscle re-education. d. Maintenance of range of motion ***3-Reduction of edema:*** - Chronic post-traumatic edema can be reduced by the use of interferential stimulation. This effect may be attributed to milking of the venous and lymphatic return through electrically-evoked contraction. The beat frequency is of approximately 15 Hz or a sweep of 10-25 Hz is often used. ***4. Increase blood flow:*** - Increased vasodilatation is noticed following interferential stimulation due to its effect on the parasympathetic nerve fibers for increased blood flow. So, interferential stimulation is used in treatment of circulatory disorders. Moreover, depressing the activity of certain cervical and lumbo-sacral sympathetic ganglia in patients with increased arterial constrictor tone, increases circulation as in Raynaud\'s disease. ***5. Stimulation of soft tissue healing and repair:*** - The interferential current accelerates ossification, so may be used to enhance fracture healing. Furthermore, it may be used also to accelerate wound healing by improving the cellular function and increasing cell proliferation. **[Indications of Interferential Current:]** **I -Peripheral vascular disease (PVD)** - **Vasoconstrictive disease (Raynaud\'s Disease)**: A disorder where the exposure to cold causes sudden contraction of small arteries supplying the fingers and toes. - **Venous insufficiency**: Inability of veins to pump the blood towards the heart. - **Burger\'s disease:** It is a combination of thrombosis, inflammation and obliteration of small and medium sized arteries. The disease begins in distal small arteries and spreads upwards. **2-Facial nerve neuritis** **3-Orthopedic conditions:** -Joint sprains -Fracture complications like delayed union, non-union & retarded callous formation. -Osteoarthritis -Spondylosis -Frozen shoulder -Chondromalacia **4-Gynecological Problems:** -Stress incontinence -Urinary frequency -Pelvic floor dysfunction **5-Pain (All types of musculoskeletal pains)** -Low back pain -Sciatica -Brachial neuralgia -Phantom limb pain - Myalgia **6-Myositis, Bursitis, and tendonitis** **7-Muscle re-education and muscle strengthening** **[Contraindications:]** a. Malignant tumors b. Deep Vein Thrombosis c. Infective conditions d. Artificial pacemakers on the heart e. Pregnant Uterus f. Condition of hemorrhage g. Large open wounds; these will cause concentration of the current and distortion of the IF field h. Dermatological conditions i. Senile or confused patients **[Russian current]** - Russian current is Medium-frequency polyphasic AC. Russian current is simply a variation of alternating current. Conventional Russian current as described by Kots is a 2,500 Hz alternating sinusoidal current that is interrupted and delivered in short bursts. - This is termed burst modulatian and is a defining characteristic of Russian current. The bursts are delivered at 50 bursts per second with a burst duration of 10 msec and an interburst interval of 10 msec. - The original Russian 10/50/10 protocol calls for 10-second contraction time and 50-second off-time for 10 repetitions. Because the burst duration is equal to the interburst interval, Russian current is often described as having a 50% duty cycle.(Fig.13a&b)  C:\\Users\\Marwa Taher\\Pictures\\Saved Pictures\\russian 1.png **Fig.13a&b: Russian current with polyphasic alternating current**  ***Difference between low frequency and Russian current*** **[Aussie current]** Aussie current is a medium frequency polyphasic AC current with a frequency 1 KHz (1000 Hz). It is burst modulated with the bursts delivered at 50 bursts per second with burst duration of 4 msec and an interburst interval of 16 msec and duty cycle 20%. The cycle duration 1 msec and phase duration 500µsec. Both Aussie Current and Russian currents are used clinically for muscle strengthening. Aussie Current differs to Russian current by the duty cycle; \"Russian Current\" and \"Aussie Current\" both have a burst frequency of 50Hz, but their differences lie in their duty cycles.(Fig.14) C:\\Users\\Marwa Taher\\Pictures\\Saved Pictures\\russian 2.png **Fig.14: Aussie current** - Russian current\'s duty cycle is at 50% whereas Aussie Current has a duty cycle of 20%, meaning the duration of stimulus changes from 10ms with Russian Current to 4ms with Aussie current. The rationale behind this is that the lower duration caused the least discomfort to the patients. These differences can be seen below in. - When comparing between kilohertz (KHz) currents regarding force production and discomfort; 1KHz is best from the point of view of force production but that 4 kHz is best for minimizing discomfort. Dufy cycle also affects force production and discomfort, with a duty cycle of 20% found to be best for force production, whereas the least discomfort was produced with duty cycles around 50%. (Fig.15a&b)  C:\\Users\\Marwa Taher\\Pictures\\Saved Pictures\\aussie current.png **Fig.15a&b: Interferential, Russian and Aussie currents** **[Theoretical basis:]** Maximum electrical stimulation can cause nearly all motor units in a muscle to contract synchronously, which cannot achieved in voluntary contraction. This would allow stronger muscle contractions to occur with electrical stimulation and hence greater muscle hypertrophy. The frequency (pulse per second or in this case, burst per second) i.e. burst contains 10-25 cycles of alternating current. This would make the muscle respond with a twitch rather than a gradually increasing contraction. Gradually increasing the numbers of bursts interrupts the mechanical relaxation cycle of the muscle and causes more shortening to take place. ***[Advantages of the currents]*** - Because the current is fast oscillating alternating as soon as the nerve repolarizes, it is stimulated again producing a current that will maximally summate muscle contraction. - The higher frequency of the current reduces the resistance to the current, which make this current comfortable enough. - The interburst interval allows tolerance of greater current intensity. - Although it is medium frequency current the nerves are stimulated because it is interrupted to give a low frequency stimulation of 50 Hz. - It can achieve muscle hypertrophy by using currents of high intensities producing maximum tolerable muscle contraction are given in spells of a few seconds separated by somewhat longer rest periods. **[Indications:]** ***The primary indication is to strengthen the muscle groups.*** **[Contraindications:]** a. **Malignancy** b. **Hemorrhage** c. **Pacemaker** d. **Pregnancy** e. **Cancer** f. **Recent Radiotherapy**