Bioelectronic medicine, or electroceuticals, is a rapidly developing therapeutic field in which biomedical devices are used electrically to block, record, or stimulate neural activity as an alternative to drugs.
The rapid evolution of technology enables dramatic improvements in what treatments and diagnostic tools are available to both human clinicians and vets. Bioelectronics have been used to help improve the lives of human patients with disabilities and diseases for quite some time. An example many people will be familiar with is the portable glucose monitor, which allows diabetic patients to measure – and consequently have greater control over – their blood sugar levels. In neurology, electrical stimulation used to treat patients with Parkinson’s disease, epilepsy and essential tremor. Bioelectronics has even allowed the blind to see.
In patients with debilitating diseases like arthritis, vagus nerve stimulation (VNS) is used to activate the cholinergic anti-inflammatory pathway in the vagus nerve, which results in reduced inflammations.
Pharmaceutical and surgical intervention are not always as effective as we would like or desirable, especially in species that are extremely sensitive to drugs, such as horses. Bioelectronic medicine allows us to intervene to help patients without the risks associated with other interventions. A prime target for such interventions is the cervical vagus nerve, which innervates various visceral organs and muscles, including the pharynx, larynx, heart, lungs, and gastrointestinal tract.
There are a numerous existing and potential impacts of this research, spanning diagnosis, monitoring and treatments, for veterinary patients as well as humans.
In equine veterinary practice, recurrent laryngeal neuropathy (RLN) is frequently seen. The term ‘laryngeal paralysis’ is sometimes used, but recurrent laryngeal neuropathy is a more accurate term, as immobility of both sides of the larynx is not present. As the nerve’s function declines, the muscles that open the larynx start to weaken with a consequent narrowing of the airway. This results in sounds being emitted, ranging from a whistle to a roar or gasping noise, especially at speed. Since air intake can be affected, horses often perform poorly when exercising.
The most commonly used existing treatment is aimed at restoring the diameter of the airway by ‘tying back’ the larynx in an open position at surgery. However, the success rate is only around 50% and many horses develop complications following surgery, including chronic lower airway disease (because their swallowing is affected) or the surgery fails and needs to be repeated. These complications can be career ending in competition horses. A significant progress in treatment has involved electrical stimulation of the affected muscle in the larynx. Functional Electrical Stimulation (FES) is used to directly stimulate the weakened muscle so that it contracts more strongly, both when stimulated electrically, but also with normal nerve stimulation.
In particular, the goal of FES is to produce a contraction that mimics a natural muscle contraction, without the need for the ‘tie back’ procedure, so that horses retain the ability to swallow effectively (thereby preventing the lower airway disease). There have been significant improvements in FES technology over the last decade, including the miniaturisation of implants. Eight weeks of stimulation in completely denervated muscle has been shown to halt muscle atrophy and increase the diameter of muscle fibres.
|Functional electrical stimulation following nerve injury in a large animal model||Muscle & Nerve||2019|
|Functional electrical stimulation leads to increased volume of the aged thyroarytenoid muscle||The Laryngoscope||2018|
|Reversing Age Related Changes of the Laryngeal Muscles by Chronic Electrostimulation of the Recurrent Laryngeal Nerve||PLoS One||2016|