Case Report
Visualization of Complex Processes in Cardiovascular System
during Electrical Auricular Vagus Nerve Stimulation
Vaiva Šiauˇci
¯
unait
˙
e
1,
* , Minvydas Ragulskis
1,
* , Alfonsas Vainoras
2
, Babak Dabiri
3
and Eugenijus Kaniusas
3
Citation: Šiauˇci
¯
unait
˙
e, V.; Ragulskis,
M.; Vainoras, A.; Dabiri, B.; Kaniusas,
E. Visualization of Complex Processes
in Cardiovascular System during
Electrical Auricular Vagus Nerve
Stimulation. Diagnostics 2021, 11,
2190. https://doi.org/10.3390/
diagnostics11122190
Academic Editor: Nikolaos Fragakis
Received: 30 October 2021
Accepted: 21 November 2021
Published: 25 November 2021
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4.0/).
1
Department of Mathematical Modelling, Kaunas University of Technology, 51368 Kaunas, Lithuania
2
Cardiology Institute, Lithuanian University of Health Sciences, 44307 Kaunas, Lithuania; alfavain@gmail.com
3
Institute of Electrodynamics, Microwave and Circuit Engineering, Vienna University of Technology,
1040 Vienna, Austria; babak.dabiri.razlighi@tuwien.ac.at (B.D.); eugenijus.kaniusas@tuwien.ac.at (E.K.)
* Correspondence: vaiva.siauciunaite@ktu.lt (V.Š.); minvydas.ragulskis@ktu.lt (M.R.)
Abstract:
The analysis of human physiological systems from the point of view of complex systems
theory remains a very ambitious task. The complexity of the problem often encourages the use of
innovative mathematical methods analyzing the processes that take place in space and time. The main
goal of this paper is to visualize the cardiovascular system during auricular vagus nerve stimulation
(aVNS) using the matrix differences to evaluate the dynamic signal interfaces by cointegrating the
initial signal data into the matrices during each case. Algebraic relationships between RR/JT and
JT/QRS cardiac intervals are used not only to track the cardiovascular changes during aVNS but
also to characterize individual features of the person during the transit through the therapy. This
paper presents the computational techniques that can visualize the complex dynamical processes
taking place in the cardiovascular system using the electrical aVNS therapy. Four healthy volunteers
participated in two verum and two placebo experiments. We discovered that the body’s reaction to
the stimulation was very different in each of the cases, but the presented techniques opened new
possibilities for a novel interpretation of the dynamics of the cardiovascular system.
Keywords: auricular vagus nerve stimulation; electrocardiography; cardiac intervals
1. Introduction
The vagus nerve (VN) is the longest cranial nerve in the human body and it is involved
in the regulation of multiple systems [
1
]. Historically, the vagus nerve has been studied as
an efferent nerve and as an antagonist of the sympathetic nervous system. Most organs
receive parasympathetic afferents through the vagus nerve and sympathetic afferents
through the splanchnic nerves. Together with the sympathetic nervous systems, the
parasympathetic nervous system is responsible for the regulation of vegetative functions
by acting in opposition to each other [
2
]. Due to this wide influence on multiple systems
and its important role in maintaining homeostasis, stimulating the VN to modulate the
function of related organs has long drawn the attention of investigators [3].
The external ear is the only place on the body where VN sends its only peripheral
branch. In fact, the auricular branch of VN surfaces as the afferent auricular VN (aVN) and,
thus, forms a cutaneous receptive field in the pinna of the ear. This field is susceptible to
external stimuli in terms of peripheral nerve stimulation. In particular, the aVN allows for
an easy external access via electrical stimulation in terms of aVNS, which then connects,
directly and favorably, the applied stimuli to the brainstem, as shown in Figure 1B. The
brainstem even mediates aVNS input to higher brain regions via extensive projections to
second and third order neurons within the brain [
4
]. The auricle, and especially its aVN
endings, might become a powerful direct gateway to modulate various brain functions,
offering the most affordable non-invasive manipulation of the central nervous system.
As shown
in Figure 1A, the middle region of the pinna, the central concha, is mostly
Diagnostics 2021, 11, 2190. https://doi.org/10.3390/diagnostics11122190 https://www.mdpi.com/journal/diagnostics
