经皮电刺激神经疗法(TENS)原理之令狐文艳创作

经皮电刺激神经疗法（TENS）原理令狐文艳TENS 经皮电刺激神经疗法经皮电刺激神经疗法是用电来刺激有疼痛症状的特定的兴奋感觉神经和刺激闸门机制和（或）内源性的阿片肽（如脑啡肽）系统。

TENS的应用方法因这些生理作用机制的不同而不同。

TENS不能保证完全达到止痛的目的，并且疼痛得到缓解的病人百分率也是会改变的，但一般情况下，急性疼痛的缓解率在65％左右，慢性疼痛则在50％左右。

但这些方法都要强于医用的安慰剂。

这种方法是非侵入性的，并且相比较药物治疗，他几乎没有副作用。

最常见的问题就是皮肤的过敏性反应（大约有2－3％的病人），这些几乎经常是由于电极的材料，传导胶体或者是固定电极的绑带引起的。

目前大部分TENS的电极是采用自粘性，预涂胶体的电极做成。

这种自粘性电极有以下几个优点，减少交叉感染的风险，易于使用，更低的过敏发生率和更低的成本。

机械参数在描述TENS是如何用于完成镇痛作用之前，先对现代机器的可获得的主要的治疗变量做一个概述。

下图是一台典型TENS 的控制器。

电流强度（A）（强度）一般在0～80mA的范围内，可是有些机器或许可以输出100mA的电流。

虽然这个机器输出的是小电流，但已经足够了，因为他的主要作用对象是感觉神经，只要有足够的电流通过组织，使感觉神经去极化，这种治疗方式就是有效的。

这台机器可以传送脉冲电流，传送这些脉冲的频率（脉冲频率B）通常在1～2个脉冲每秒到200或者250个脉冲每秒间变化。

要产生临床有效的治疗效应，建议TENS应该涵盖2～150HZ的频率。

除刺激频率以外，每个脉冲的持续时间（或宽度）在10～250μs间变化，最近的证据表面，相比强度和频率，脉冲宽度重要性要小。

另外，现代的机器提供了一个burst模式（D），使得脉冲可以以爆破或者长队的形式输出，通常在2～3个burst每秒的速率。

最后，调制模式（E）可提供所采用的方法，使输出的脉冲不规则，因此尽量减少了因规则刺激造成的机体适应效应。

之所以用如此短的脉冲来实现这些效果，是因为作用对象是感觉神经，而且往往是有较低的阈值（即他们是很容易兴奋的），并认为他们会回应快速变化的电状态。

一般不需要用较长的脉冲去使神经去极化，因此，小于一毫秒的刺激是足够的。

大部分机器提供两通道，两副电极可以同时刺激。

在某些情况下，这是一个明显的优势，尽管有意思的是大部分的病人和治疗师趋向于应用单通道。

不同的厂家生死的TENS产生的脉冲波会不同，但往往是不对称的改良的双相方波脉冲。

双相性脉冲意味着通常没有净直流电成分，从而避免了由于电极下的点解产物的堆积所造成的皮肤反应。

作用机理这种类型的刺激旨在刺激感觉神经，这样一来，启动特异的自然镇痛机制。

为了方便起见，如果认为有两个主要的镇痛机制，可以激活闸门控制机制和内源性的阿片系统，要考虑到刺激这两个不同的系统所需的参数是有差异的。

用闸门控制机制来镇痛的方法涉及激活感觉纤维，这样做，减少了从“C”纤维从脊髓向高级中枢传输的有害刺激。

Aβ纤维似乎正在增加至一个比较高频率的刺激（以90～130HZ orpps）。

很难对每一个病人找到一个产生最好镇痛效果的单一频率，但90～130HZ这样的频率对于大部分的个体都适用。

另一种方法是刺激Δ纤维，一种以较低频率（2～5HZ）刺激会优先作出反应的纤维，将启动阿片机制，并通过脊髓释放一种内源性的阿片（脑磷脂）来镇痛，从而减轻有害感觉通路的激化作用。

第三种可能性是，由雇用burst模式在同一时间刺激两种神经类型。

在这种情况下，较高频率的刺激输出（通常在100HZ 左右）会中断（或爆破）的频率约为2～3个burst每秒。

当机器开着，他会提供100HZ的脉冲，因此激活了β纤维和闸门控制机制，但由于burst的发生频率2～3HZ，会兴奋Δ纤维，从而刺激了阿片系统。

对于某些病人来说，这是到目前为止最有效的镇痛方法，尽管这有些不可思议，众多的病人发现这比其他形式的TENS不容易接受。

TENS模式传统TENS通常使用的刺激相对较高的频率（90～130HZ），并使用相对窄的脉冲宽度（开始约100ms），但如上所述，在目前正在进行的研究项目文献中很少由支持脉冲时间操纵的。

刺激以正常的强度传递，绝对有但不会不舒服。

30分钟或许是最小限度的有效时间，根据需要可以尽可能长时间的延长治疗时间。

镇痛最重要的是在刺激的过程中，并且有一个有限的延续效应――即机器关掉后，疼痛仍然可以得到缓解。

电针型TENS使用频率较低的刺激（2～5HZ）和较宽的脉冲（200～250ms）。

这种使用强度通常比传统的TENS强度大，但仍然不是病人的极限，但是相当明确的，强有力的感觉。

如前所述，30分钟是有治疗效果的最少治疗时间。

需要有一段时间来刺激阿片的分泌达到足够的量，因此镇痛效果的起效可能会比传统模式慢。

一旦有足够的阿片释放，他将在刺激停止后依然持续发挥作用。

许多病人觉得以低频率在一天中不时的刺激是一个有效的策略。

他的延续作用可能会持续好几个小时。

短暂强刺激型TENS这是一个TENS模式，可以用来实现快速镇痛，但有些病人可能会觉得刺激的强度太剧烈，无法坚持忍受到出现治疗效果的那段时间。

脉冲频率应用高（90～130HZ）和脉冲持续时间也高（200ms以上）。

电流接近于病人容忍的水平，这样他们就不会再想把机器调的更高。

这样，能量传递给病人相对其他模式时高。

建议在这样的刺激强度下的治疗，15～30分钟是最普遍使用的治疗时间。

触发模式TENS如上所述，机器发送传统的TENS，但burst模式打开，因此以2～3burst每秒的频率发放来中断电刺激。

刺激强度必须在相对高的情况下，虽然不如短暂强烈型TENS那样高，更像电针型lo TENS的强度。

频率的选择以上各种模式指南，它可能不适合去确定特定的频率用来达到某一特定效果。

如果用一个单一的频率作用于每一个人，将容易很多，但研究并不支持这个观点。

病人（或者治疗师）需要去发现最有效的镇痛频率，操作频率盘或按钮是最好的发现最佳频率的方法，如果不进行调节把盘和按钮放置一边，这样的话很难达到最佳效果。

刺激强度如上面发现的，不可能用多少微安来描述治疗电流强度。

最有效的强度指标是参照病人在治疗时的感觉。

通常来说，Hi TENS的治疗强度是让患者有明确的但无痛的刺激感，Lo TENS 的治疗强度则是强烈的但无痛的刺激感。

电极放置：对于这种治疗方法，为了获得最大的治疗效益，把刺激电极放置在疼痛的相应脊髓水平。

把电极放置在损伤的任何一侧或疼痛区域，以获得最好的镇痛效果，是最常见的做法。

研究还报道了其他一些有效的放置方法，大多数是放置在相当的神经根水平：刺激适当神经根刺激外周神经刺激运动点刺激触发点或针刺点刺激适当的（同一脊神经支配的）皮区，肌肉区，骨区如果疼痛的来源是模糊的，散在的或者是特别广泛的，可以同时使用两个通道，2通道应用也可以有效的处理局部＋牵涉痛的联合疼痛，每一个通道用于一个部位。

禁忌症不理解物理治疗师的指导的病人或者不协作的病人孕妇的躯干，腹部或骨盆。

TENS用于产痛例外。

带起搏器的病人对电极，凝胶体或绑带有过敏反应的病人皮肤条件：比如皮炎，湿疹病人目前或者最近出血或有循环障碍，比如组织局部出血，血栓及相关条件电极放在颈部或颈动脉窦注意事项如果有反常的皮肤反应，电极要放在更适宜的位置确保有效的刺激电极不能放在眼部患有癫痫症的病人需咨询相关医生，并由治疗师做出判断避免儿童的骨骺活跃区在分娩时使用腹部电极会干扰胎儿的监测设备Transcutaneous Electrical Nerve Stimulation (TENS) TENS is a method of electrical stimulation which primarily aims to provide a degree of pain relief (symptomatic) by specifically exciting sensory nerves and thereby stimulating either the pain gate mechanism and/or the opioid system. The different methods of applying TENS relate to these different physiological mechanisms. Success is not guaranteed with TENS, and the percentage of patients who obtain pain relief will vary, but would typically be in the region of 65%+ for acute pains and 50%+ for more chronic pains. Both of these are better than the placebo effect.The technique is non invasive and has few side effects when compared with drug therapy. The most commoncomplaint is an allergic type skin reaction (about 2-3% of patients) and this is almost always due to the material of the electrodes, the conductive gel or the tape employed to hold the electrodes in place. Most TENS applications are now made using self adhesive, pre gelled electrodes which have several advantages including reduced cross infection risk, ease of application, lower allergy incidence rates and lower overall cost.Machine parameters:Before attempting to describe how TENS can be employed to achieve pain relief, the main treatment variables which are available on modern machines will be outlined. The location of these controls on a typical TENS machine is illustrated in the diagram.The current intensity (A) (strength) will typically be in the range of 0 - 80 mA, though some machines may provide outputs up to 100mA. Although this is a small current, it is sufficient because the primary target for the therapy is the sensory nerves, and so long as sufficient current is passed through the tissues to depolarise these nerves, the modality can be effective.The machine will deliver ‘pulses’ of electrical energy, and the rate of delivery of these pulses (the pulse rate (B) will normally be variable from about 1 or 2 pulses per second (pps) up to 200 or 250 pps. To be clinically effective, it is suggested that the TENS machine should cover a rate from about 2 – 150Hz.In addition to the stimulation rate, the duration (or width) of each pulse (C) may be varied from about 40 to 250 micro seconds (ms). (a micro second is a millionth of a second). Recent evidence would suggest that this is possibly a less important control that the intensity or the frequency.In addition, most modern machines will offer a BURST mode(D)in which the pulses will be allowed out in bursts or ‘trains’, usually at a rate of 2 - 3 bursts per second. Finally, a modulation mode (E) may be available which employs a method of making the pulse output less regular and therefore minimising the accommodation effects which are often encountered with this type of stimulation.The reason that such short duration pulses can be used to achieve these effects is that the targets are thesensory nerves which tend to have relatively low thresholds ( i.e. they are quite easy to excite) and that they will respond to a rapid change of electrical state. There is generally no need to apply a prolonged pulse in order to force the nerve to depolarise, therefore stimulation for less than a millisecond is sufficient.Most machines offer a dual channel output - i.e. two pairs of electrodes can be stimulated simultaneously. In some circumstances this can be a distinct advantage, though it is interesting that most patients and therapists tend to use just a single channel application.The pulses delivered by TENS stimulators vary between manufacturers, but tend to be asymmetrical biphasic modified square wave pulses. The biphasic nature of the pulse means that there is usually no net DC component, thus minimising any skin reactions due to the build up of electrolytes under the electrodes. Mechanism of Action :The type of stimulation delivered by the TENS unit aims to excite (stimulate) the sensory nerves, and byso doing, activate specific natural pain relief mechanisms. For convenience, if one considers that there are two primary pain relief mechanisms which can be activated : the Pain Gate Mechanism and the Endogenous Opioid System, the variation in stimulation parameters used to activate these two systems will be briefly considered.Pain relief by means of the pain gate mechanism involves activation (excitation) of the A beta 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 A beta fibres appear to appreciate being stimulated at a relatively high rate (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.An alternative approach is to stimulate the A delta fibres which respond preferentially to a much lower rate of stimulation (in the order of 2 - 5 Hz), which will activate the opioid mechanisms, and provide painrelief by causing the release of an endogenous opiate (encephalin) in the spinal cord which will reduce the activation of the noxious sensory pathways.A third possibility is to stimulate both nerve types at the same time by employing a burst mode stimulation. In this instance, the higher frequency stimulation output (typically at about 100Hz) is interrupted (or burst) at the rate of about 2 - 3 bursts per second. When the machine is ‘on’, it will deliver pulses at the 100Hz rate, thereby activating the A beta fibres and the pain gate mechanism, but by virtue of the rate of the burst, each burst will produce excitation in the A delta fibres, therefore stimulating the opioid mechanisms. For some patients this is by far the most effective approach to pain relief, though s a sensation, numerous patients find it less acceptable than the other forms of TENS.TENS ModesTraditional TENS (Hi TENS, Normal TENS)Usually use stimulation at a relatively high frequency (90 - 130Hz) and employ a relatively narrow pulse width (start at about 100ms) though as mentionedabove, there is less support for manipulation of the pulse width in the current research literature. The stimulation is delivered at ‘normal’ intensity- definitely there but not uncomfortable. 30 minutes is probably the minimal effective time, but it can be delivered for as long as needed. The main pain relief is achieved during the stimulation, with a limited ‘carry over’ effect –i.e. pain relief after the machine has been switched off.Acupuncture TENS (Lo TENS, AcuTENS)Use a lower frequency stimulation (2-5Hz)with wider (longer) pulses (200-250ms). The intensity employed will usually need to be greater than with the traditional TENS - still not at the patients threshold, but quite a definite, strong sensation. As previously, something like 30 minutes will need to be delivered as a minimally effective dose. It takes some time for the opioid levels to build up with this type of TENS and hence the onset of pain relief may be slower than with the traditional mode. Once sufficient opioid has been released however, it will keep on working after cessation of the stimulation. Many patients find thatstimulation at this low frequency at intervals throughout the day is an effective strategy. The ‘carry over’ ef fect may last for several hours.Brief Intense TENS :This a TENS mode that can be employed to achieve a rapid pain relief, but some patients may find the strength of the stimulation too intense and will not tolerate it for sufficient duration to make the treatment worthwhile. The pulse frequency applied is high (in the 90-130Hz band) and the pulse width is also high (200ms plus). The current is delivered at, or close to the tolerance level for the patient - such that they would not want the machine turned up any higher. In this way, the energy delivery to the patients is relatively high when compared with the other approaches. It is suggested that 15 - 30 minutes at this stimulation level is the most that would normally be used.Burst Mode TENS :As described above, the machine is set to deliver traditional TENS, but the Burst mode is switched in, therefore interrupting the stimulation outflow at rateof 2 - 3 bursts / second. The stimulation intensity will need to be relatively high, though not as high as the brief intense TENS – more like the lo TENS.Return to TopFrequency Selection :With all of the above mode guides, it is probably inappropriate to identify very specific frequencies that need to be applied to achieve a particular effect. If there was a single frequency that worked for everybody, it would be much easier, but the research does not support this concept. Patients (or the therapist) need to identify the most effective frequency for their pain, and manipulation of the stimulation frequency dial or button is the best way to achieve this. Patients who are told to leave the dials alone are less likely to achieve optimal effects.Stimulation Intensity: As identified above, it is not possible to describe treatment current strength in terms of how many microamps. The most effective intensity management appears to be related to what the patient feels during the stimulation, and this may vary from session tosession. As a general guide, it appears to be effective to go for a ‘definitely there but not painful’ level for the normal (high) TENS, and a ‘strong but not painful’ level for the acupuncture (lo) mode.Electrode placement :In order to get the maximal benefit from the modality, target the stimulus at the appropriate spinal cord level (appropriate to the pain). Placing the electrodes either side of the lesion – or pain areas, is the most common mechanism employed to achieve this. There are many alternatives that have been researched and found to be effective –most of which are based on the appropriate nerve root level :Stimulation of appropriate nerve root(s) Stimulate the peripheral nerve Stimulate motor point Stimulate trigger point(s) or acupuncture point(s) Stimulate the appropriate dermatome, myotome or sclerotomeIf the pain source is vague, diffuse or particularly extensive, one can employ both channels simultaneously.A 2 channel application can also be effective for the management of a local + a referred pain combination –one channel used for each component. CONTRAINDICATIONSPatients who do not comprehend the physiotherapist’s instructions or who are unable to co-operateApplication of the electrodes over the trunk, abdomen or pelvis during pregnancy except if using TENS for labour pain(see recent changes to this guidance - DOWNLOAD TENS Guidelines During PREGNANCY document) Patients with a PacemakerPatients who have an allergic response to the electrodes, gel or tapeDermatological conditions e.g. dermatitis, eczema Patients with current or recent bleeding / haemorrhage or with compromised circulation e.g. ischaemic tissue, thrombosis and associated conditionsApplication over the anterior aspect of the neck or carotid sinusPRECAUTIONSIf there is abnormal skin sensation, the electrodes should preferably be positioned in a site other than this area to ensure effective stimulationElectrodes should not be placed over the eyesPatients who have epilepsy should be treated at the discretion of the physiotherapist in consultation with the appropriate medical practitionerAvoid active epiphyseal regions in childrenThe use of abdominal electrodes during labour may interfere with foetal monitoring equipment。