经皮电刺激神经疗法(TENS)原理

经皮电刺激神经疗法(TENS)原理TENS 经皮电刺激神经疗法经皮电刺激神经疗法就是用电来刺激有疼痛症状得特定得兴奋感觉神经与刺激闸门机制与(或)内源性得阿片肽(如脑啡肽)系统。

TENS得应用方法因这些生理作用机制得不同而不同。

TENS不能保证完全达到止痛得目得,并且疼痛得到缓解得病人百分率也就是会改变得,但一般情况下,急性疼痛得缓解率在65％左右,慢性疼痛则在50％左右。

但这些方法都要强于医用得安慰剂。

这种方法就是非侵入性得,并且相比较药物治疗,她几乎没有副作用。

最常见得问题就就是皮肤得过敏性反应(大约有2－3％得病人),这些几乎经常就是由于电极得材料,传导胶体或者就是固定电极得绑带引起得。

目前大部分TENS得电极就是采用自粘性,预涂胶体得电极做成。

这种自粘性电极有以下几个优点,减少交叉感染得风险,易于使用,更低得过敏发生率与更低得成本。

机械参数在描述TENS就是如何用于完成镇痛作用之前,先对现代机器得可获得得主要得治疗变量做一个概述。

下图就是一台典型TENS得控制器。

电流强度(A)(强度)一般在0～80mA得范围内,可就是有些机器或许可以输出100mA得电流。

虽然这个机器输出得就是小电流,但已经足够了,因为她得主要作用对象就是感觉神经,只要有足够得电流通过组织,使感觉神经去极化,这种治疗方式就就是有效得。

这台机器可以传送脉冲电流,传送这些脉冲得频率(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。

要产生临床有效得治疗效应,建议TENS应该涵盖2～150HZ得频率。

除刺激频率以外,每个脉冲得持续时间(或宽度)在10～250μs间变化,最近得证据表面,相比强度与频率,脉冲宽度重要性要小。

另外,现代得机器提供了一个burst模式(D),使得脉冲可以以爆破或者长队得形式输出,通常在2～3个burst每秒得速率。

最后,调制模式(E)可提供所采用得方法,使输出得脉冲不规则,因此尽量减少了因规则刺激造成得机体适应效应。

之所以用如此短得脉冲来实现这些效果,就是因为作用对象就是感觉神经,而且往往就是有较低得阈值(即她们就是很容易兴奋得),并认为她们会回应快速变化得电状态。

一般不需要用较长得脉冲去使神经去极化,因此,小于一毫秒得刺激就是足够得。

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,这就是一个明显得优势,尽管有意思得就是大部分得病人与治疗师趋向于应用单通道。

不同得厂家生死得TENS产生得脉冲波会不同,但往往就是不对称得改良得双相方波脉冲。

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得点解产物得堆积所造成得皮肤反应。

作用机理这种类型得刺激旨在刺激感觉神经,这样一来,启动特异得自然镇痛机制。

为了方便起见,如果认为有两个主要得镇痛机制,可以激活闸门控制机制与内源性得阿片系统,要考虑到刺激这两个不同得系统所需得参数就是有差异得。

用闸门控制机制来镇痛得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得有害刺激。

Aβ纤维似乎正在增加至一个比较高频率得刺激(以90～130HZ or pps)。

很难对每一个病人找到一个产生最好镇痛效果得单一频率,但90～130HZ这样得频率对于大部分得个体都适用。

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

第三种可能性就是,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,较高频率得刺激输出(通常在100HZ左右)会中断(或爆破)得频率约为2～3个burst每秒。

当机器开着,她会提供100HZ得脉冲,因此激活了β纤维与闸门控制机制,但由于burst得发生频率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,这就是到目前为止最有效得镇痛方法,尽管这有些不可思议,众多得病人发现这比其她形式得TENS不容易接受。

TENS模式传统TENS通常使用得刺激相对较高得频率(90～130HZ),并使用相对窄得脉冲宽度(开始约100ms),但如上所述,在目前正在进行得研究项目文献中很少由支持脉冲时间操纵得。

刺激以正常得强度传递,绝对有但不会不舒服。

30分钟或许就是最小限度得有效时间,根据需要可以尽可能长时间得延长治疗时间。

镇痛最重要得就是在刺激得过程中,并且有一个有限得延续效应――即机器关掉后,疼痛仍然可以得到缓解。

电针型TENS使用频率较低得刺激(2～5HZ)与较宽得脉冲(200～250ms)。

这种使用强度通常比传统得TENS强度大,但仍然不就是病人得极限,但就是相当明确得,强有力得感觉。

如前所述,30分钟就是有治疗效果得最少治疗时间。

需要有一段时间来刺激阿片得分泌达到足够得量,因此镇痛效果得起效可能会比传统模式慢。

一旦有足够得阿片释放,她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得刺激就是一个有效得策略。

她得延续作用可能会持续好几个小时。

短暂强刺激型TENS这就是一个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得强度太剧烈,无法坚持忍受到出现治疗效果得那段时间。

脉冲频率应用高(90～130HZ)与脉冲持续时间也高(200ms以上)。

电流接近于病人容忍得水平,这样她们就不会再想把机器调得更高。

这样,能量传递给病人相对其她模式时高。

建议在这样得刺激强度下得治疗,15～30分钟就是最普遍使用得治疗时间。

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

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

频率得选择以上各种模式指南,它可能不适合去确定特定得频率用来达到某一特定效果。

如果用一个单一得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)需要去发现最有效得镇痛频率,操作频率盘或按钮就是最好得发现最佳频率得方法,如果不进行调节把盘与按钮放置一边,这样得话很难达到最佳效果。

刺激强度如上面发现得,不可能用多少微安来描述治疗电流强度。

最有效得强度指标就是参照病人在治疗时得感觉。

通常来说,Hi TENS得治疗强度就是让患者有明确得但无痛得刺激感,Lo TENS得治疗强度则就是强烈得但无痛得刺激感。

电极放置:对于这种治疗方法,为了获得最大得治疗效益,把刺激电极放置在疼痛得相应脊髓水平。

把电极放置在损伤得任何一侧或疼痛区域,以获得最好得镇痛效果,就是最常见得做法。

研究还报道了其她一些有效得放置方法,大多数就是放置在相当得神经根水平: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得(同一脊神经支配得)皮区,肌肉区,骨区如果疼痛得来源就是模糊得,散在得或者就是特别广泛得,可以同时使用两个通道,2通道应用也可以有效得处理局部＋牵涉痛得联合疼痛,每一个通道用于一个部位。

禁忌症不理解物理治疗师得指导得病人或者不协作得病人孕妇得躯干,腹部或骨盆。

TENS用于产痛例外。

带起搏器得病人对电极,凝胶体或绑带有过敏反应得病人皮肤条件: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得皮肤反应,电极要放在更适宜得位置确保有效得刺激电极不能放在眼部患有癫痫症得病人需咨询相关医生,并由治疗师做出判断避免儿童得骨骺活跃区在分娩时使用腹部电极会干扰胎儿得监测设备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 pared with drug therapy、The most mon plaint 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 acmodation 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 the sensory 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 ponent, 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 by so 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 henc e 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 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、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 burstsper 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 mentioned above, 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 unfortable、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 that stimulation at this low frequency at intervals throughout the day is an effective strategy、The ‘carry over’ effect 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, theenergy delivery to the patients is relatively high when pared 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 rate of 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 to session、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 mon 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 nerveStimulate motor pointStimulate 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 bination –one channel used for eachponent、CONTRAINDICATIONSPatients who do not prehend 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, eczemaPatients with current or recent bleeding / haemorrhage or with promised circulation e、g、ischaemic tissue, thrombosis and associated conditionsApplication over the anterior aspect of the neck or carotid sinus PRECAUTIONSIf 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。