Transcutaneous Electric Nerve Stimulation (TENS) for Vagal Modulation

A Pilot Study of Auricular Microstimulation to Determine if it Improves Vagal Modulation

This study is to determine if the auricular microstimulator produces the expected increase in HRV.

The aim of this proposal is to determine if utilizing an affordable tool like microstimulation utilizing a transcutaneous electric nerve stimulator (TENS) unit and applying the stimulation to the ear though an ear clip does improve vagal modulation. This can be easily done at home by utilizing the microstimulation for 2 hours/day and measuring vagal modulation before and after. Previous research investigating this had participants use the unit for 2 hours as well (Chelimsky et al., 2019), however the data from this study was inconclusive, and therefore this study aims to demonstrate effectiveness of the unit usage on heart rate variability (HRV).

Although functional gastrointestinal disorders (FGID) affect 10%-20% of children and adolescents. 1-3 the pathophysiology remains unknown. The multiple current hypotheses include visceral hypersensitivity, altered brain-gut connections, dysbiosis, genetic and epigenetic factors, and increased gut permeability among others. 4 Since the vagus nerve links the brain to the gut, many studies of adult subjects have evaluated the cardiovagal modulation in this group of disorders. The cardiovagal modulation can be measured by heart rate variability (HRV). HRV evaluates the heart rate fluctuation over a period of time. HRV is considered a reliable tool to look at parasympathetic function, baroreflex function, and parasympathetic to sympathetic balance.5, 6 High-frequency (hf) HRV is a marker of vagal modulation. The low-frequency (lf) HRV probably reflects cardiac autonomic outflow from the baroreflex or parasympathetic regulation, rather than sympathetic modulation, although this is still being discussed.6, 7

A meta-analysis of adult subjects with irritable bowel syndrome (IBS) showed decreased cardiovagal modulation.8 One study compared children aged 7-10 years of age with functional abdominal pain or IBS to healthy subjects. They found no difference in cardiovagal and cardiac sympathetic modulation.9 However, a study of young adolescents with different chronic pain syndromes, including chronic abdominal pain, showed decreased cardiovagal modulation.10 These findings are similar to those in many adult syndromes with chronic pain, such as chronic pelvic pain,11 complex regional pain syndrome,12 fibromyalgia,13 and chronic neck pain.14

Although future research would aim to investigate vagal modulation in those specifically with FGID, for preliminary data purposes we are testing the unit's effects on heart rate variability regardless of having/not having an FGID diagnosis.

Inclusion Criteria:

• Female
• 12 - 21 years old
• Either diagnosed OR not diagnosed with chronic idiopathic nausea, functional abdominal pain, dyspepsia and/or irritable bowel syndrome.
• English speaking

Exclusion Criteria:

• Patients who are unable to stand upright during the heart rate variability recording
• Patients with a known bleeding disorder
• Patients with swollen, infected, inflamed, or other skin eruptions on outer ear
• Patients with epilepsy
• Patients with any implanted cardiac pacemaker or defibrillator
• Patients with serious arterial circulatory problems in the lower limbs
• Patients with abdominal or inguinal hernia
• Patients who are pregnant
• Any unstable medical condition, such as renal disease, uncontrolled diabetes, etc.
• Requires new medication during the 4 weeks of the study that may affect the gastrointestinal symptoms, vagal modulation or immune response.
• Practices over 1 hour of aerobic activity a day
• Daily practice of abdominal breathing (yoga)