TENS Under the Hood: Past and Future

07/29/2020 • Shai Gozani M.D., Ph.D.

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This is the last post in our series exploring how TENS (Transcutaneous Electrical Nerve Stimulation) devices work. Our intention has been to go “under the hood” of these valuable pain relief devices to help you understand their operation.  We explored key technical specifications and operating principles. We hope this information is useful when deciding on a TENS device for your particular needs.

In the final post we “close the hood” and take a step back to briefly consider the history and future of TENS technology.  Read on to learn about electrical eels, the Magneto-Electric machine, Dr. Normal Shealy and likely directions for TENS innovation.

A Brief History of Electrotherapy

TENS is a branch of electrotherapy which means the treatment of disease using electricity, as opposed to drugs or chemicals.  Although this may seem like a novel idea that belongs in the 21st century, electrotherapy dates back thousands of years to the ancient Romans and Greeks. Physicians in ancient Greece discovered that electrical impulses emitted from electric eels in foot baths relieved pain, arthritis and improved blood circulation.  Amazingly, electric eels can generate up to 600 volts in a discharge.

Other than the use of electric leeches in the dark ages, little further happened in electrotherapy until the 18th and 19th centuries when physiologists discovered that many biological systems, such as the heart and nervous system, utilized electrical signaling.  This led to an explosion of commercial electrotherapy devices that were peddled for every possible ailment, including pain.  Among the most popular such devices was the Magneto–Electric machine that was developed in the US and initially commercialized in the 1850s.

Magneto–Electric Machine, circa 1854 – 1870

The manufacturer claimed that the device could relieve pain, as well as cure cancer, tuberculosis, diabetes, gangrene, heart disease, tetanus, and others.  An operator turned the crank which generated an alternating current to the patient through the two handles, with the magnitude proportional to the rotational speed.  As the proud owner of a Magneto-Electric machine, I doubt the health claims but can confirm that it still generates quite a jolt after 150 years.

Modern TENS Devices

The modern TENS device is credited to Dr. Normal Shealy in the early 1970s.  As a neurosurgeon, Dr. Shealy was initially motivated to develop a screening technique for predicting which chronic pain patients would respond to implantable stimulators before proceeding to surgery. However, it quickly became apparent that a significant percentage of patients attained substantial pain relief from TENS alone.  Dr. Shealy inspired the development of several early commercial TENS devices including the Neuromod® device manufactured and sold by Medtronic, Inc. in the 1970s.

Neuromod TENS Device from Medtronic, Inc.

A comparison of the Neuromod and other TENS units from the 1970s with modern TENS shows that today’s devices have become smaller, transitioned from analog to digital electronics, replaced dials and knobs with push buttons and LCDs, and adopted better battery technology.  However, their fundamental operation has not changed.  In typical use, the pain sufferer still attaches the device to electrodes on the skin via lead wires, dials up the intensity, and the device proceeds to stimulate for some period of time.  Quell® wearable pain relief technology, launched in 2015, represented the first fundamental innovation in TENS technology in decades.

The Future of TENS Technology

Lacking a crystal ball, we can only offer educated guesses as to how TENS technology will evolve in the near future.  First, we anticipate that the devices will become increasingly wearable, along the lines of Quell.  To maximize the pain relief benefits of TENS, the devices must fit into to the user’s life rather than the other way around.  Wearable devices allow users to go about their daily activities uninterrupted and even use TENS while sleeping.  However, achieving true wearability is difficult.  It requires development of small but powerful devices that are discreet and comfortable.  It requires smart devices which automate the manual tasks that users must undertake with typical TENS.  Automation is challenging and requires sophisticated algorithms and body sensors, such as accelerometers.  And, as for other wearables like smart watches, adequate battery life is critical.

Another direction for TENS technology is integration with mobile devices.  Like Quell, several TENS devices support Bluetooth and communicate with mobile apps running on Apple and Android smartphones and tablets.  At a basic level, these mobile apps serve as a sophisticated remote control.  However, the potential benefits of mobile apps go much further.  For example, they can help guide users to optimally use the associated device, monitor and motivate adherence to improve pain relief, track user reported outcomes such as pain relief and quality of life which can provide feedback to the user and their physician, and connect users with others in the pain community to help break the isolation felt by so many pain sufferers.  The possibilities are unlimited, and we expect that substantial innovation will occur with TENS associated mobile apps.

Finally, we believe that more high quality clinical studies will be conducted to confirm and expand on the clinical utility of TENS for pain in general, and chronic pain specifically.  Although TENS devices have been used for five decades and thousands of studies have been conducted, controversy remains over their efficacy.  Unfortunately this has led insurance companies to withhold reimbursement thus limiting access for many individuals in need of pain relief.  The inconclusive evidence on TENS can be attributed to low study fidelity, which means that many of the clinical studies were performed with ineffective TENS devices at inadequate doses.  These issues have been identified by thought leaders in TENS research and some studies conducted over the past five years have improved and yielded definitive positive results.

Concluding Remark

TENS has been used for five decades and helped millions of people suffering from pain.  Although the field has not historically been one of great innovation, recent trends are encouraging.  TENS represents a safe, non-pharmacological approach to pain management.  Given the dual challenges of the chronic pain and opioid misuse epidemics, TENS holds great promise and has a bright future.

If you would like to read more posts in the TENS Under the Hood series, please click here.

©2020 NeuroMetrix, Inc. All Rights Reserved.


About The Author
Shai Gozani M.D., Ph.D.
Shai Gozani M.D., Ph.D.

Dr. Gozani is an expert in non-invasive neurostimulation. He received his M.D. degree from Harvard Medical School and the Harvard-MIT Division of Health Science and Technology. Dr. Gozani earned his Ph.D. in Neurobiology, M.S. in Electrical Engineering & Computer Science and B.A. in Computer Science from the University of California at Berkeley. Following his studies, Dr. Gozani conducted post-doctoral research at Harvard Medical School and MIT. He holds 36 U.S. patents and has authored over 30 articles in scientific and clinical peer-reviewed journals. Dr. Gozani is founder, president and CEO of NeuroMetrix, Inc.; which designs and manufactures Quell.


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