Comparative Effect of Vagal Stimulation on Heart Rate, Blood Pressure, and Skin Hydration at Different Anatomical Sites in Prehypertensive Individuals: A Pilot Study

Abstract

Introduction: Prehypertension is the precursor to high Blood Pressure (BP), which can lead to severe consequences such as cardiovascular disease, stroke, acute myocardial infarction, heart failure, peripheral arterial disease, and cerebrovascular complications, ultimately resulting in mortality. Vagal stimulation is frequently employed by therapists, along with various therapeutic exercises, to treat or manage Heart Rate (HR) and BP in prehypertensive individuals. The vagus nerve plays a vital role in maintaining internal physiological balance, known as homeostasis, which includes reflex pathways that regulate cardiac function. Auricular neuromodulation of the vagus nerve can be achieved through stimulation of the ear lobule, cymba concha, or tragus in the outer ear. Aim: To compare and determine the optimal anatomical site for vagal stimulation, specifically the ear lobule, cymba concha, or tragus, to improve HR, BP, and skin hydration in prehypertensive individuals. Materials and Methods: The present pilot study conducted a pre-post comparative analysis in the Outpatient Department (OPD) of Physiotherapy at the Institute of Applied Medicines and Research Centre, Ghaziabad, Uttar Pradesh, India. The study duration was nine months, from January 2022 to September 2022. A total of 30 subjects aged 30-55 years were divided into three groups (10 participants in each group: A, B, and C) using sealed envelopes. Group A received vagal stimulation on the ear lobule, Group B received vagal stimulation on the cymba concha, and Group C received vagal stimulation on the tragus. Baseline measurements were taken prior to treatment, including HR, BP, and skin hydration. Vagal stimulation was administered using a low-frequency Transcutaneous Electrical Nerve Stimulation (TENS) machine at 25 Hertz and a pulse width of 120 ms. The stimulus was continuously applied for 30 minutes, five days a week, for four weeks. After a 10-minute relaxation period, HR, BP, and skin hydration were measured both pre and post-intervention. The data was statistically analysed using Statistical Package for Social Sciences (SPSS) version 24.0, employing paired t-tests to compare means within groups and Analysis of Variance (ANOVA) to compare between the three groups. Results: There were no statistical differences in the baseline among all three groups. Group C, which received vagal stimulation on the tragus, demonstrated statistically significant improvements in BP and skin hydration. The t-value and p-value for Systolic Blood Pressure (SBP) were 11.513 and p<0.001, for Diastolic Blood Pressure (DBP) were 10.411 and p<0.001, for HR were 15.231 and p<0.001, and for skin hydration were 9.474 and p<0.001, respectively. When comparing HR, BP, and skin hydration among the groups using one-way ANOVA f- value and p-value showed significant difference between the groups in all parameters. Conclusion: The study concludes that vagal stimulation on the tragus is a superior intervention compared to vagal stimulation on the cymba concha or ear lobule for controlling HR, BP, and skin hydration in prehypertensive individuals.