David L. Snyder, MD, Tufts Medical Center, Boston MA
Wearable medical technology provides valuable information and functionality for patients. The first wearable medical device was eyeglasses with convex lenses, invented in Italy during the 13th century. Their development for the visually impaired paved the way for other wearable devices to address medical problems—from hearing aids to insulin pumps. Modern commercial devices have expanded on a simple pedometer and altimeter technology to track physical activity in the context of promoting a healthy lifestyle as a form of primary prevention. And if we expand our scope to include minimally invasive implantable devices, then the potential for patient benefit is even greater. For example, cardiac pacemakers and defibrillators can sense, interpret, and intervene on pathological electrical activity in the heart to ultimately save lives.
The current wearable medical technology market includes devices like watches, available to the public, that have pulse oximetry, electrocardiography, and sleep tracking capabilities. But what makes modern devices truly special is their capacity to collect vast amounts of data. Wearable biosensors can transmit surveillance data and integrate real-time communication with physicians. This data gives physicians more insight into their patient’s disease course and increases the potential for more personalized care. It is no surprise then that the wearable medical device market is estimated to be worth almost 90 billion dollars by 20271.
"The devices themselves are catching up with the trend towards commercially appealing high-tech by becoming sleeker, providing more options"
For chronic pain, a wearable device likely to dominate the market is the transcutaneous electrical nerve stimulation (TENS) unit—a non-pharmacological, therapeutic electrical stimulation device that addresses localized, neuropathic pain. Neuropathic pain is defined as pain that is derived from injury or insult to the physical nerve, commonly seen in chronic conditions like peripheral vascular disease, direct trauma, or chronic nerve impingement from degenerative lumbar spine disease. Patients describe the sensation as burning or “pins and needles,” and it can be accompanied by an exaggerated or inappropriate response to minimally painful or non-painful stimuli. Neuropathic pain is estimated to have a prevalence ranging between 3 percent and 17 percent in the general population2.
There are two theories for the effectiveness of transcutaneous electrical stimulation. The first is the local release of endogenous endorphins3 which are natural hormones created by the body that, when released, bind to opioid receptors causing an analgesic effect. The second is the blockage of pain signal transmission through local nerve stimulation, which modifies pain perception— known commonly as Gate Control theory. This idea is based on the concept that peripheral nerves connect to the spine like roads merging into a highway. By overwhelming or saturating the “on-ramp,” one prevents the painful stimulus from reaching the brain and eliminating its perception. This is supported by studies that show effective analgesia in patients with stimulation of the opposite, unaffected limb5..
However, the jury is still out on the effectiveness of TENS units6,7. Unfortunately, it is not possible to conduct an appropriately blinded study to compare TENS units against controls. However, because of the opioid epidemic, TENS units are becoming more popular as patients and physicians look for alternatives to pharmaceuticals8. The devices themselves are catching up with the trend towards commercially appealing high-tech by becoming sleeker, providing more options: different modes and intensities, incorporating Bluetooth® capabilities, integrating with smartphone applications, highlighting personalized aesthetics with color choices, and packaging that rivals the latest smartphone9. This has all ultimately led to a more marketable product.
The future of wearable and implantable medical technology in pain medicine goes beyond diagnostics and monitoring to include the deployment of immediate, automated therapies. Current devices like smart insulin pumps can sense biomarkers and make automated therapeutic adjustments to insulin infusion rates, preventing dangerous dips and peaks in blood glucose levels. Spinal cord stimulators maybe next to incorporate these higher levels of active neuromodulation by detecting the release of known biomarkers of pain like Substance P or differentiating between painful and non-painful electrical patterns in nerve transmission like how cardiac defibrillators detect malignant arrhythmias10.
When considering technology and pain medicine, we must consider devices that may help fight the opioid epidemic. It seems that such devices are currently being conceived11: implantable drug delivery systems for naloxone, an opioid receptor antagonist, with diagnostic sensing of physiologic and chemical biomarkers of life-threatening respiratory depression. This could be a gamechanger in reducing opioid-related morbidity and mortality. We know that the timely administration of intranasal naloxone by police and first responders is associated with the reduction in deaths from opioid overdose12. An automated device could improve the timely administration of this life-saving medication. Perhaps future iterations could go beyond preventing complications of opioid overdose to improving the management of opioid addiction with medications like suboxone and methadone in response to real-time biomarkers.
The world of wearable and implantable medical technologies is an exciting frontier for patients, physicians, and engineers alike. As the available technology gets smarter and smaller, the functional potential grows. Current chronic pain patients are suffering from their disease and, like many other chronic conditions, a paucity of novel therapies are available to address it. But wearable and minimally invasive implantable devices may provide answers and, more importantly, relief.