What is the Tens?
In the field of Physiotherapy, we can find many resources to reduce pain in patients using physical agents, and without doubt, one of the most used is TENS.
As the name implies, Electro transcutaneous nerve stimulation ( TENS) is a machine that can relieve pain quickly, in the prolonged application on patients with alias anywhere in the body, related to traumatic or nervous effects. Undoubtedly, the most important thing to consider about TENS is its basic physiological foundation by which it arises, which is the well-known Pain Gate system.
This nervous phenomenon is on which the TENS waves are based to generate the effect of pain reduction, it refers to the human brain can generate control over the pathways that transmit pain, closing or opening its doors, to allow feeling or avoid it. Undoubtedly, this procedure is unconscious and there is no way to handle it at will, but clearly, we can do it with external stimuli such as TENS.
The gate theory says that if the brain is being distracted, it loses the ability to pay attention to the pain caused by the source of the trauma, so it does not feel the pain. In this way the TENS works on nerve stimulations, to make the brain pay attention to these small waves, and not the source of pain so that the nociceptive pathways are completely blocked.
Obviously, when designing the TENSthey took into account the process by which the brain adapts quickly, and if so, it would stop paying “attention” to the TENS waves, and we would feel the pain again.
That is why this wonderful device can quickly vary the intensity and frequency of its wave so that the brain never adapts to its functioning, and always takes the impulses as totally new stimulations, not generating accustoming and “forgetting” the pain.
How is the Tens applied?
Basically, the TENS must be used on the area affected by the trauma, and its application is really simple since, with its electrodes that adhere to the skin, we can place them anywhere in the body. Obviously, for headaches, this process does not work, since we cannot place the electrodes in the skull.
For trauma pain, the application of TENS electrodes they can be invading the affected area, generating analgesia in the indicated place, or around the affected area, in order to block the channels of the nociceptive pathways to the brain. In the same way, in failed surgical processes or in nerve injuries, where there was no nerve section, the electrodes are placed between the lesion itself and the brain, near the affected area, to interrupt the nociceptive waves towards the central nervous system.
As the TENS is a device that transmits electricity, obviously we will handle parameters related to the area of electromagnetism, so we will have to take into account that its parameters will have:
Frequency of the impulse: Here is an important factor regarding the application of TENS waves , since the frequency can vary between 1 and 1000, but we find several authors that Siegel_EMS-TENS_2explain that less frequent waves are the best for the treatment of pain, and that between 1 and 100 Hz would be the point of maximum relief. Research conducted by Sjölund and Eriksson in 1981 gives us a frequency of 80 Hz as the ideal to combat pain.
Pulse duration: The pulse of the wave generated with the TENS should last between 60 and 150 µsec, and never but never exceed 200 µsec.
Frequency or spectrum modulation: Frequency modulation is key to the achievement of a result, and we can basically use high-frequency TENS at low amplitude to quickly generate relief and prevent nerve tissue from getting used to this process.
Burst frequency: At this point, a lot of emphases must be placed because the result of the application depends on it. Basically, if we give 100 Hz impulses, we can insert them into the so-called “wave trains” that cause the body to receive stimuli of 2 or 5 Hz, but with hidden waves of 100 Hz.
This allows it to be more penetrated into body tissue with optimal analgesic results. In this case, if the wave is 100 Hz, the stimulation time will be 125 msec, in which 75msec is of maintenance of the wave, 25 of the descent of the same to not generate an abrupt cut and 25 of rest, to allow the fibers to recover and repolarize.
Tens of Application Techniques
The TENS can be applied in two ways that clearly apply highly recommended effects on pain relief. On the one hand, the Conventional application establishes that high-frequency TENS at low amplitude effects rapid pain relief, but of short duration in patients. Undoubtedly, I know that in this case the amplitude should be fair, and should be looked for until the degree of paraesthesia is most satisfactory for the patient.
On the other hand, the burst application explains that in this method the wave trains between 2 and 5 Hz can produce pain relief effects and analgesia but only after 30 minutes of application, but the effect will last until almost 8 hours after the session.
The TENS is an incredible device that allows physiotherapists to quickly relieve the pain of their patients, especially those of traumatic origin, with a non-invasive mode of use, where the patient’s integral health is taken into account, and that does not generate adverse effects in its application, but without doubt, there are direct indications to the use of TENS .
Basically, we can’t use the tension people who have installed mark steps, because electric waves can alter its operation and therefore, generate a heart attack. On the other hand, the use of pregnant women is also prohibited, and this is because it is not known or wanted to do experiments to know how electro stimulation affects babies in gestation.
Tens in Pain Control
The use of TENS in the treatment of pain is a byproduct of the work done by Melzack and Wall in 1965, which describes the Pain Gate Theory. In this theory, the electric current applied to the nerve endings in the skin, travels to the brain through selective nerve fibers (A-fibers). These fibers pass through the spinal cord gelatinous substance and which contains specialized cells (T cells) in the neural transmission and that A-fibers assist in the conduction of ascending pain sensations to the thalamus (“pain center” of the brain).
The small C fibers, which carry the pain signal, have a lower transmission speed than the A fibers, whose signal normally reaches the brain before the transmission of the C fibers, thus blocking the painful sensation. T cells are considered as gates through which signals must pass, while the transmission overhead of fibers A blocks the slower transmission of fibers C.
Tension Modes and Parameters
Conventional or High-Frequency Mode
According to Kitchen (2003), this type of stimulation aims to selectively activate wide-diameter Aβ fibers without simultaneously activating Aγ and C fibers, of small diameters and related to pain. It is characterized by a high frequency, from 60 to 100 PPS, and by a low amplitude of stimulation, less than 100 μs, with a sensory intensity which causes comfortable skin paraesthesia, without muscle contraction and activates the pain modulating door at the level of the medulla (in the case of women).
For the kitchen (2003) the frequency is between 10 and 200 PPS with a duration of 100-200 μs, the placement of the electrodes should be on the place of pain or dermatome, the duration of the treatment as necessary, the start and the term for it pain relief is fast, less than 30 minutes after being connected and after switching off, respectively.
The conventional mode of TENS is effective in the treatment of acute soft tissue injury, pain associated with musculoskeletal disorders, postoperative, inflammatory and myofascial pain (STARKEY, 2001).
Tens acupuncture or burst or low-frequency mode:
It consists of low pulse frequencies, 2 to 4 PPS, with a long pulse duration of 100 to 300 μs and motor level intensity activating motor fibers and small diameter nociceptors. According to Starkey (2001: 237), that mode ” stimulates the pituitary gland to release chemicals that stimulate the production of β-endorphins that reduce pain.” This occurs because the pituitary gland releases adrenocorticotropic hormone and β-lipotropin that in turn release β-endorphins that bind to the Aβ and C fibers, blocking the passage of pain.
Stimulation in this mode should cause comfortable muscle contraction to the patient, the duration of treatment is approximately 30 minutes, the electrodes must be placed on the motor point, on the pain or myotome, and its analgesia lasts hours after being disconnected. Low TENS can be used for chronic pain, pain caused by deep tissue injury, myofascial pain and muscle spasm (KITCHEN, 2003).
The Tens is released in high pulse rate, greater than 100 PPS, and long-lasting pulse, 300 to 1,000 μs and intensity at the motor level, with treatment duration between 15 to 30 minutes, pain relief after treatment is less than 30 minutes, and it is recommended to reduce pain before therapeutic exercises. Pain relief with this mode is obtained by forming a negative feedback loop inside the central nervous system that generally inhibits the release of substance P, a neurotransmitter that causes pain
electrode placement methods for TENS include:
Direct placement on the skin, in the painful place or around it, the channels being arranged in parallel;
Adjacent placement, in which the electrodes are applied in the vicinity of the pain, with the electrodes parallel or perpendicular to the pain center;
Placement in stimulation points such as motor, trigger and acupuncture points;
Placement in dermatomes, one electrode being placed in the root of the corresponding nerve and the other in the distal termination of the dermatome;
Placement at the level of the spinal cord, the electrode is placed parallel to the spinal column, between the transverse processes;
Indications and Contraindications
TENS, in general, is used in the treatment of acute pain, as in the cases of postoperative, obstetric pain, dysmenorrhea, musculoskeletal pain, bone fracture, and dental procedures. It is also used, in cases of chronic pain such as lumbago, arthritis, Coto and phantom pain, neuralgia, peripheral nerve injury, facial pain, metastatic bone pain, and angina pectoris.
Contraindications include pain of unknown origin, in people with pacemakers or heart disease, epilepsy, in the first trimester of pregnancy, on the carotid sinus, damaged or dysesthetic skin or internally in the mouth