Medical devices to deliver transcutaneous electrical stimulation using interferential current to treat constipation

Keywords::

• bowel motility
• electrotherapeutics
• physical therapy
• physiotherapy

Transcutaneous electrical stimulation (TES) is a well-known method used by physiotherapists to treat pain and muscle injury. Interferential current (IFC) is a special type of TES using two currents that cross and produce a beating effect [1]. TES-IFC has been used for over 20 years to treat bladder over-activity and urinary incontinence and to strengthen the pelvic floor [2–5]. When used for urinary incontinence, TES also produced diarrhea, leading physiotherapist Janet Chase, who specialized in incontinence, to test TES on children with chronic constipation [6]. Since that study, published in the year 2005, IFC has been used to treat a number of bowel motility disorders including dyspepsia [7], irritable bowel syndrome [8], slow transit constipation in children [9–14] and adults [11] and constipation in children with myelomeningocele (a type of spina bifida) [15]. In the colon, TES-IFC increased the colonic motility, sped up colonic transit, increased the sensation of the urge to defecate, increased the defecation frequency and reduced soiling and bloating.

There are many TES devices on sale. Physiotherapists use devices that are plugged into AC (220/240 V) power. Battery-operated devices that can be used at home are available on the Internet. There is a wide range of quality products available but only a few are able to deliver IFC.

Our initial studies on constipation used a device, common in physiotherapy clinics, the Metron Vectorsurge (Australia). This device can deliver current via two or four electrodes. It delivers interferential, premodulated, TENS and Russian stimulation. It delivers IFC at 2500, 4000 or 10,000 Hz carrier frequency. This device is plugged into the AC power supply and allows complete control by the clinician. Because it is difficult for patients to attend clinic every day, treatment was given three-times a week for 20 min and the total number of sessions was 12. Using the stimulation parameters that produced diarrhea during bladder treatment, we gave stimulation using two channels (channel one at 4000 Hz, channel two varying from 4080–4150 Hz, at a comfortable setting of 20–30 mAmps) using 4 cm × 4 cm carbon rubber electrodes. TES-IFC increased defecation and stopped soiling in five of eight children with chronic constipation and improvements lasted for more than 3 months in some children [6]. In a larger group, there were similar improvements and a slight increase in transit speed and improved quality of life [9–10,16]. Colonic contractions increased [16] and improvements lasted up to 2 years [17]. A recent detailed review of our studies is available free online [101].

Battery-operated IFC devices became available in the mid-2000s. With these, the patient/parent can give stimulation at home, allowing daily stimulation for a longer time (commonly 1 h). Eleven children, who previously had stimulation three-times a week without success, underwent daily treatment for 2 months, leading to an increase in defecation frequency into the normal range in nine children [12]. In a larger group of 32 children, with treatment-resistant constipation, when given daily stimulation for 3–6 months, more than half of the children showed increased defecation into the normal range and stopped soiling [13].

Three battery-operated IFC devices have been reported for bowel stimulation. Firstly we used Fuji Dynamics IF 4160 (Hong Kong). From the year 2008–2012, we used the model FD09. This delivered current from a 9 V rechargeable battery. In the mid of 2012, a new model was released, FD-10, that uses four 1.5 V single-use batteries or can be plugged into AC power. We only used the FD-10 on AC power to provide enough current for 1 h of treatment. This device is available in Australia and UK. Other groups have used NOVIN model 510 A (Isfahan, Islamic Republic of Iran) [15,18] and Ito EU-940 (Germany) [8] with good results. A comparison among the output of the devices would be useful.

Electrical current delivery depends on the electrodes and many types are available. Electrodes can be long-use types made of carbon rubber and used with suction [8] or with wet sponge pads [6] or can be silicon-coated disposable electrodes [13]. Different sizes have been used including 2.3 × 3.5 cm and 4 × 4 cm. They have been placed with two electrodes on the front and two on the back, at the level of the belly button [8–10,13,15–16,101] or over the lower pelvic zone [18] or with four on the back [7]. For home use, it is important that patients should be trained in electrode use. If they use disposable electrodes, it is important that they are sticky and should create a good contact with the skin. Body hair should be removed for best results.

To produce the highest level evidence, randomized-control trials (RCTs) are required. Two RCTs have been performed [9–10,15]. It is not easy to perform a blinded study for a treatment that can be felt by the patient, that lasts for months and is delivered at home by the patient. Some of the major points of concern are: How can you blind the person delivering the treatment?; How can you blind the patient?; What placebo can be used?; and what features can be measured to get an objective measure of improvement? Patients can record through diaries but for the evidence-base it is preferable to have objective measures also. Those measures used so far, include transit studies [16], gastric emptying [7], anorectal manometry [15] or colonic manometry [16] to measure the rate of movement through the bowel or strength or frequency of contractions. Questionnaires are also used to measure the changes in bowel symptoms or quality of life [9,15].

User difficulties

For home-use, it is important that patients are trained to use the device correctly. Physiotherapists are trained to use the electrical therapy but for other clinicians, we found that it takes 5–10 patients to learn what to do. Ian Yik, a surgeon, reported that it took six patients for him to learn how to teach them, to use the portable machine correctly and to make sure that the patients had recorded their daily diary and passed it to the clinician [13]. We have surveyed patients and found that they have problems in choosing the right settings on devices and may connect the leads incorrectly so that currents do not cross.

Mechanism of action

It remains to be determined whether TES-IFC is acting via spinal pathways, sensory nerves, enteric nerves, interstitial cell of Cajal or hormonal systems. Motor control of the intestine is very complex [101]. Motor activity of the gut is determined by muscle cells, pacemaker cells (interstitial cells of Cajal), nerves and hormones. The intestine contains its own nerve cell network (the enteric nervous system) and has connections to the Central Nervous System (CNS) via the vagal, splanchnic and pelvic nerves. These carry sympathetic, parasympathetic and sensory nerve fibres [19]. Sympathetic innervation inhibits bowel motility, while parasympathetic innervation activates the bowel. [20]. Spinal nerves (S2-4) carry parasympathetic outflow to the rectum and internal anal sphincter, somatic innervation to the anal sphincter muscle (striated muscle) and sensory fibres to the CNS [19]. Direct electrical stimulation of these nerves (using implanted electrodes) is sufficient to activate bowel motility reflexes. For example, in patients with spinal injuries, sacral nerve stimulation initiates colonic contraction producing movement of feces into the anal canal, resulting in reflex pelvic floor relaxation and evacuation of the rectum [20]. TES-IFC would be expected to stimulate these nerves, but might also have effects within the intestine. Animal models are needed to investigate the mechanism of action.

Ward has studied IFC and thresholds for sensory nerves, pain and muscle contraction. He presented a detailed discussion of the myths and realities of IFC [1]. Interferential stimulators produce two independent currents applied by two pairs of electrodes, positioned diagonally. It is commonly claimed that there is a maximum stimulation in the region of intersection of the currents but Ward argues that the stimulus experienced by a nerve fiber may be continuous (unmodulated), fully modulated or partially modulated depending on the fiber location and orientation relative to the electrodes. The stimulation intensity experienced by nerve fibers has a maximum modulation if the fibers are oriented optimally and zero modulation when fibers are oriented along one of the current pathways [1]. Ward showed that stimulation of nerves that innervate striated muscle at 100 Hz or more, results in fatigue and reduction in torque in the muscle and can also inhibit the release of acetylcholine [21]. Ward also showed that that premodulated IFC, delivered via two large electrodes, may be clinically more effective than the traditional true IFC arrangement in terms of depth efficiency, torque production and patient comfort [22]. None of these factors have been measured for abdominal stimulation and bowel activity.

Future perspective

Transcutaneous stimulation of the intestine is a new use for an established but poorly characterized or understood method. In the next 5 years there should be an expansion in its use to increase intestinal motility and with that, many of the parameters for its use and mechanism of action should be addressed. This is a new field and there are many unknown opportunities for improvement in devices and treatment parameters. There are still many issues to resolve about the optimal use of IFC devices for bowel motility, including current settings, electrode position and treatment frequency. These aspects require active study. There is also much scope for future improvements in devices that are easier for patients to use, feedback that electrodes are delivering adequate current or which ones are not, determining optimal placement of electrodes, and for studies that determine where current goes, what are the best electrical parameters for stimulation, what time of day is best to do stimulation and which patients will benefit from IFC treatment.

It looks like TES-IFC could be a useful treatment for patients with bowel motility disorders and should add to the techniques available especially for treatment-resistant patients. The method can be used for children and the elderly, it is cheap (<US$500), non-invasive and has no side effects. We will also see the development of devices specifically for use on the bowel in the next few years.

Financial & competing interests disclosure

BR Southwell holds patents on the method of transcutaneous electrical stimulation to treat constipation. She has received Australian Government National Health and Medical Research (NHMRC) grants to study the effect of transcutaneous electrical stimulation on children with slow-transit constipation and with anorectal retention and to develop an electrical stimulation device specifically to treat constipation. She has received investment from the Medical Research Commercialization Fund to develop the device and created a startup company – GI Therapies (Melbourne, Australia) – to develop and test a prototype device. The author has no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.