J. ROZMAN et al.: MEASUREMENT OF BASIC HEMODYNAMICS DURING MULTIPOST TRANSCUTANEOUS ...
309–319
MEASUREMENT OF BASIC HEMODYNAMICS DURING
MULTIPOST TRANSCUTANEOUS EXTERNAL EAR
STIMULATION: A TWO-CASE STUDY
MERITEV OSNOVNE HEMODINAMIKE MED VE^TO^KOVNO
TRANSKUTANO STIMULACIJO ZUNANJEGA U[ESA: [TUDIJA
NA DVEH OSEBAH
Janez Rozman
1,2*
, Katarina Miklavec
2
, Ingrid Rozman
3
, Anja Emri
4
,
Tomislav Mirkovi}
5
, Samo Ribari~
2
1
Center for Implantable Technology and Sensors, ITIS d. o. o. Ljubljana, Lepi pot 11, 1000 Ljubljana, Slovenia
2
Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Zalo{ka 4, 1000 Ljubljana, Slovenia
3
The Family Study and Research Centre, Dvor 12, 1210 Ljubljana-[entvid, Slovenia
4
Medical Chamber of Slovenia, Dunajska cesta 162, 1000 Ljubljana, Slovenia
5
Department of Anaesthesiology and Surgical Intensive Therapy, University Medical Centre Ljubljana, Zalo{ka 2, 1000 Ljubljana, Slovenia
Prejem rokopisa – received: 2023-10-26; sprejem za objavo – accepted for publication: 2024-04-04
doi:10.17222/mit.2023.1032
The objectives of the investigation were to assess the short-term responses of the cardio-vascular system on the multipost
transcutaneous stimulation (tANS) of the external ear (EE). The scope was to measure the forefinger photopleths (FPPG), toe
photopleths (TPPG), aortic phonocardiogram (APCG), mitral phonocardiogram (MPCG) and brachial arterial blood pressure
(BABP), assuming that they could be altered with the tANS. For the tANS, stimulator, two silicone ear plugs with four platinum
electrodes each, and a large common electrode (CE), were used. Trials were carried out with two female volunteers, aged
25 years and 28 years. To capture the heart sounds, two customized electronic stethoscopes (transducers) were used. BABP was
measured using a pressure transducer and blood-pressure appliance. To measure the FPPGs, a pulse oximeter and SpO2 finger
clip were used. To measure the TPPGs, another pulse oximeter and customized SpO2 foot clip was used. Signals were gathered
using a high-performance data-acquisition system. An offline analysis was made just before and just after the start of the tANS.
To record the pulsations in the right brachial artery, the 2D ultrasound mode (B) of the ultrasound device was used before and
during the tANS. Then, diagrams showing the vein cross-sectional area over time were constructed. The results show that vascu-
lar time intervals between heart sounds S1 and S2, captured as APCG and systolic peaks of the FPPG in the second volunteer,
were slightly larger during the separate tANS of the left white (LW) and (RW) EE post than before the tANS. Furthermore, vas-
cular time intervals between the heart sounds S1 and S2, captured as MPCG and systolic peaks of the TPPG in the second vol-
unteer, were slightly smaller during the separate tANS of LW and RW EE post than before the tANS. Finally, tANS of the LW
post elicited a slightly lower heart rate than the one measured when LW was not stimulated. In contrast, the tANS of the RW
post elicited a slightly higher heart rate than the one measured when RW was not stimulated. It was also shown that the pattern
of the vein cross-sectional area over time with tANS was different compared to both the FPPG and TPPG.
Keywords: external ear stimulation, hemodynamics, measurement, signal acquisition
Cilj raziskave je bil ovrednotiti kratkoro~ne odzive sr~no-`ilnega sistema na ve~to~kovno transkutano stimulacijo (tANS)
zunanjega u{esa (EE). Raziskava je obsegala meritve fotopletismogramov na palcu desne roke (FPPG), fotopletismogramov na
palcu leve noge (TPPG), aortnih fonokardiogramov (APCG), mitralnih fonokardiogramov (MPCG) in brahialnega arterijskaga
krvnega tlaka (BABP) predpostavljajo~, da se bodo spremenili vsled tANS. Za tANS so bili uporabljeni stimulator, dva u{esna
~epka iz silikona s po {tirimi platinastimi ektrodami in velika skupna elektroda (CE). Meritve so bile opravljene na dveh
prostovoljkah starih 25 let in 28 let. Za zajemanje zvokov srca sta bila uporabljena dva posebej izdelana elektronska stetoskopa
(transducer). BABP pa je bil merjen s pretvornikom tlaka in merilcem krvnega tlaka. Za meritve FPPG je bil uporabljen pulzni
oksimeter z naprstnim SpO2 senzorjem. Za meritve TPPG pa je bil uporabljen drugi pulzni oksimeter s posebnim SpO2
senzorjem na no`nem palcu. Signali so bili digitalizirani z zmogljivim sistemom za zajemanje podatkov. Kasnej{a analiza
podatkov je bila narejena tik pred za~etkom in takoj po kon~ani tANS. Za bele`enje pulziranja desne brahijalne arterije je bil
uporabljen 2D ultrazvo~ni na~in (B) ultrazvo~ne naprave in sicer pred in med tANS. Nato sta bila konstruirana diagrama, ki sta
prikazovala presek arterije v odvisnosti od ~asa. Rezultati so pokazali, da so bili ~asovni intervali med zvoki srca S1 in S2 zajeti
kot APCG in sistoli~nimi vrhi pri drugi prostovoljki, rahlo dalj{i tako med tANS levega belega (LW) kot tudi desnega (RW)
mesta na EE, kot pred tANS. Nadalje so bili ~asovni intervali med zvoki srca S1 in S2 zajeti kot MPCG in sistoli~nimi vrhi pri
isti prostovoljki, rahlo kraj{i tako med tANS levega belega (LW) kot tudi desnega (RW) mesta na EE, kot pred tANS. Razen
navedenega je pri{lo v ~asu tANS mesta LW do rahlega zmanj{anja frekvenc sr~nega utripa kot je bil v ~asu brez tANS.
Nasprotno pa je pri{lo v ~asu tANS mesta RW do rahlega pove~anja ritma srca kot je bil v ~asu brez tANS. Rezultati so tudi
pokazali, da je bil ~asovni potek sprememb povr{ine prereza arterije v odvisnosti od ~asa med tANS razli~en tako od poteka
FPPG kot tudi od poteka TPPG.
Klju~ne beside: stimulacija zunanjega u{esa, hemodinamika, meritev, zajemanje signala
Materiali in tehnologije / Materials and technology 58 (2024) 3, 309–319 309
UDK 616.288:612.063 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 58(3)309(2024)
*Corresponding author's e-mail:
jnzrzmn6@gmail.com (Janez Rozman)

1 INTRODUCTION
Electrical nerve stimulation is the most often used
technique to provide external control over body systems
that are normally under the control of the nervous sys-
tem.
1
Surgically implanted devices currently used for the
stimulation of vagus nerve afferents have many disad-
vantages. It was presumed, however, that most of them
can be overcome using the novel method of trans-
cutaneous vagus nerve stimulation tVNS.
2
Thus, tVNS
devices that target the auricular (tANS) portion of the
vagus nerve may have the potential to be implemented
for rehabilitation, and treatment of physiological and
mental disorders.
3
Namely, tANS technology targets
afferents within the auricular branch of the vagus nerve
that can be accessed from the external ear (EE).
4
Some
studies reported effects of the tANS on the regulation of
autonomic function through measurements of the heart
rate, heart-rate variability, blood pressure, and related
physiological quantities in healthy volunteers and in vas-
cular hypertensive patients.
5
One non-invasive procedure used to describe the
heart-function dynamics is phonocardiography (PCG). It
is the graphical representation of heart sounds providing
information useful to reveal abnormalities in the move-
ment of the heart wall, closure of the valves, or the leak-
age of blood flow.
6
In this regard, the PCG can be uti-
lized to auscultate and distinguish four sounds during the
heart cycle, i.e., S1, S2, S3, and S4, that arise from open-
ing and closing of a valve.
7
Traditional positions of heart
auscultation at the thorax are the following: the mitral
area above the cardiac apex, the tricuspid area above the
fourth and fifth intercostal space along the left sternal
border, the pulmonic area above the second intercostal
space along the left sternal border and aortic area above
the second intercostal space along the right sternal bor-
der. Heart sounds are complex and non-stationary subtle
body sounds. They can be described by their intensity,
pitch, position, quality and timing in the heart cycle.
8
Loudness of the heart is usually measured in decibels
(dB) based on how far away a tested person is. To assess
the heart function, a heart-sound activity detection
framework has been developed by Varghees et al.
9
The
authors captured PCG signals that included four heart
sounds: S1, S2, S3 and S4. They also identified average
heart sound durations, the time delay between heart
sounds, and the duration of heart cycles. Finally, they
identified normal frequency ranges of heart sounds (S1
(50–150) Hz, S2 (50–200) Hz, S3 (50–90) Hz, and S4
(50–80) Hz). Fast Fourier transform (FFT) was used for
automatic heart-sound signal analysis. In healthy sub-
jects, the two heart sounds, S1 and S2, are the most fre-
quently used in the PCG analysis.
10
S1 results from the
closing of the mitral and tricuspid valves. The sound pro-
duced by the closure of the mitral valve is termed M1,
and the sound produced by the closure of the tricuspid
valve is termed T1. M1 is the main component of S1 and
is much louder than T1. S2, however, is produced by the
closure of the aortic and pulmonic valves where the clo-
sure of the aortic valve is termed A2, and the closure of
the pulmonic valve is termed P2. A2 is normally much
louder than P2 and is the main component of S2. In gen-
eral, heart valves have been considered passive structures
that only function in response to the hemodynamic
forces generated by heart contractions.
11
However, under
physiological conditions, autonomic sympathetic nerves
and the vagus nerve modulate the mechanical properties
of heart valves. However, little focus has been given to
the regulation of heart valves by the autonomic nervous
system.
12
As the mitral valve is exposed to high mechani-
cal forces during each heart cycle, it can be hypothesized
that under such physiological conditions, mitral valve
tissue stiffness varies in response to autonomic nervous
agents and that the leaflet tone and valve function are
modulated. Therefore, there is a need to identify the role
of the autonomic nerve in the regulation of mitral valve
mechanical properties.
Oximeters used in pulse oximetry
13
often provide a
patient’s heart rate via an assessment of the arterial blood
pulsations. Pulse oximeters are also able to visualize a
blood-volume change in the tissue caused by the passage
of blood, and this is called a plethysmographic trace. It
can resemble an arterial pressure waveform and is ap-
proximated by the ratio of the stroke volume output to
the compliance of the arterial tree. In clinical practice,
photoplethysmography (PPG) is routinely used to moni-
tor cardiac-induced blood volume changes at peripheral
body sites, such as the finger, forehead, earlobe, and
toe.
14
A normal PPG is characterized by a sharp systolic
upstroke and peak and by a prominent dicrotic notch on
the downward portion of the PPG. With compromised
blood flow through an artery, however, the dicrotic notch
can be lost or reshaped. A photoplethysmograph is often
used to measure an optical PPG. It offers a simple and
inexpensive method to detect blood-volume changes in
the microvascular bed of tissue and to measure toe blood
pressure.
15
In critically ill or hemodynamically unstable patients,
however, there is a frequent need for hemodynamic mon-
itoring such as cardiac output, oxygen saturation, and
stroke volume variation. Hemodynamic monitoring is a
procedure used in the repeated assessment of circulatory
function to check blood circulation and to evaluate how
well a heart is working over time.
16
The results of a
hemodynamic test demonstrate how much blood a heart
can pump and how well blood travels through the blood
vessels. They can thus identify problems and suggest
possibilities to address them. With this regard, the ultra-
sound mode that is normally used to study vasculature is
the two-dimensional (2-D) (B) mode. It uses the echo
from solid structures to display 2-D images of the walls
of blood vessels.
17
Data obtained by the most sophisti-
cated duplex ultrasound instrument can show macro-
vascular features of vascular physiology including imag-
ing and flow velocity profiles.
J. ROZMAN et al.: MEASUREMENT OF BASIC HEMODYNAMICS DURING MULTIPOST TRANSCUTANEOUS ...
310 Materiali in tehnologije / Materials and technology 58 (2024) 3, 309–319

The present study was aimed at testing whether the
multi post tANS of afferent nerve fibres within the auric-
ular branch of the vagus nerve can be used as a method
for the external modulation of basic hemodynamic func-
tion. The main goal was to identify, record and analyse
the short-term responses of the cardio-vascular system
on the multipost tANS. The specific goal was to retain
the characteristics of the main events within the mea-
sured signals and to analyse them if they contained
extractable information resulting from the tANS. With
regard to the cardio-vascular system, the aim was to
measure the forefinger photopleths (FPPG), toe photo-
pleths (TPPG), PCG, and Brachial artery blood pressure
(BABP), assuming that all can be altered with the tANS.
2 EXPERIMENTAL PART
2.1 Protocol Approval, Subject Consent and Subject
Health Status
This study was conducted on two female volunteers,
aged 25 and 28 years. Anthropometric data for the first
volunteer: age 25 years, height 174 cm, weight 63 kg,
non-smoker, systolic blood pressure 115 mmHg and
heart rate 60/min. Anthropometric data for the second
volunteer: age 28 years, height 160 cm, weight 50 kg,
non-smoker, systolic blood pressure 110 mmHg and
heart rate 56/min. Both were in top physical condition
and were free from any known cardio-vascular disease.
They were recruited by asking them to participate in the
study. Each participant was recruited for the study at dif-
ferent times. We carried out the study approved by the
National Medical Ethics Committee, Ministry of Health,
Republic of Slovenia (No. 0120-297/2018/6).
2.2 Medical isolation and noise reduction
The entire setup was connected to the human by con-
sidering the class safety standard (IEC 60601: Interna-
tional Product Safety Standards for Medical Devices). To
accomplish the galvanical isolation between the mains
supply section and that of the measuring setup section,
the highest quality vintage 500 VA isolation transformer
(supplied in 1966 with the STM-200-b studio Reel-to-
Reel Mono Tape Recorder for professional use,
Mechanikai Laboratórium (ML), Budapest, Hungary),
was used. The isolation transformer used has a leakage
current of 15 μA which was within the range of trans-
formers rated for medical applications (between 10 and
50 μA). This power supply isolation also enabled a break
of the ground loops and thereby the elimination of noise
in the measuring setup. To additionally inhibit the noise
transmitted through the grid power cable and high-fre-
quency interference signals generated by the electronic
device itself, the CE Certified Single-Phase 220V AC,
15A, EMI Power Supply Filter (EMI Filter) with
Dual-Stage S Purification (CW4L2-I5A-S, Canny Well
Co., Ltd., No. 333, Jen Chian St., Shu-Lin 23855, Tai-
wan, China) was used.
2.3 Multipost transcutaneous stimulation set-up
For the multi post tANS, the certified microproces-
sor-controlled stimulator (Model SM9079, Shenzhen
L-Domas Technology Ltd., Shenzhen, Guangdong,
China) was used. The pattern of the stimuli train was se-
lected from a palette of patterns available with the
stimulator. The proprietary stimulating pulse was sym-
metrical, current-regulated rectangular and dual direc-
tional stimulating pulse pair. The parameters selected at
the stimulator were the following:
Frequency f = 45.5 Hz,
Stimulating phase width tc = 200 μs,
Anodic phase width ta = 200 μs,
On time (pulse train duration) 3.32 s,
Time gap between pulses train 2.8 s.
To deliver the stimuli to a particular post at the EE,
the negative output of the stimulator was connected to
the corresponding electrode using a custom-developed
switching unit. The common anode (CE), however, was
connected to the positive output of the stimulator. For the
multipost tANS, the two silicone ear plugs, having four
platinum electrodes each, were developed. They were
mounted onto the frame of the headphones and inserted
J. ROZMAN et al.: MEASUREMENT OF BASIC HEMODYNAMICS DURING MULTIPOST TRANSCUTANEOUS ...
Materiali in tehnologije / Materials and technology 58 (2024) 3, 309–319 311
Figure 1: Stimulating system: a) stimulating plug, b) frame of head-
phones with stimulating plugs, c) electrical stimulator, d) switching
unit, e) common anode

into the EE such that each cathode was in contact with
the predefined post at the EE. The reusable CE was
crafted using a 2-mm-thick, 300-mm-long and
25-mm-wide ribbon made of highly water-absorptive
sponge that was stitched below the stainless-steel mesh
and Velcro tape. The geometric surface of the anode was
approximately 7500 mm
2
. When wetted, the approxi-
mately 3-mm-thick anode contacted the skin as a homo-
geneous conductive solution. The components of the
stimulating system are shown in Figure 1.
Despite the fact that the tANS was delivered via a
battery-powered stimulator, tANS generated relatively
large electric fields that propagated through the body to-
wards the sensors of the measuring set-up. Fortunately,
the sensors applied were out of the galvanic contact with
the skin so the signals recorded could not be contami-
nated by electrical artefacts. To eliminate any potential
interference, the neck was selected as the location to at-
tach the CE and the subject grounded. Thus, the location
was away from the sensors, and it separated galvanically
the head from the body via thick bone and other tissues
at a relatively small cross-section of the neck.
2.4 Measuring devices and procedures
To build the multi-channel measuring set-up, various
custom-designed and commercially available devices
were used. To capture heart sounds (PCG), two cus-
tom-developed transducers were used. Brachial arterial
blood pressure (BABP) was measured using a pressure
transducer and commercial blood-pressure appliance. To
measure the forefinger pleths (FPPG), a pulse oximeter
and an adult SpO2 finger clip were used. To measure the
toe pleths (TPPG), a pulse oximeter and customized
photo-plethysmography foot clip were used. To record
the blood flow in the brachial artery, the most advanced
portable diagnostic ultrasound device was used. Signals
were gathered using a high-performance I/O data-acqui-
sition system and portable computer.
2.4.1 Auscultation of heart sounds
To capture the PCG that came from the heart valves,
two custom-developed transducers shown in Figure 2a
were used (frequency range 20–20,000 Hz, analogue
voltage output 0.2–1 V). To distinguish types of sounds
namely, S1 and S2,
18
two transducers were placed at the
standard heart auscultation positions shown in Figure 3.
The first transducer was placed at the aortic heart
auscultation position located at the 2
nd
right intercostal
space of the ribs near the sternum. The second transducer
was placed at the mitral or apex heart auscultation posi-
tion located at the 5
th
left intercostal space of the ribs and
in the middle of the clavicular line. To reduce the effect
of high-frequency noises, the PCG signals were filtered
using a low-pass filter (LPF) Butterworth, 10–300 Hz, 3
rd
with cut-off frequency of 300 Hz.
19,20
The transducers
were used to potentially differentiate types of particular
valve sounds that may be modified with the tANS. For
the calibration of both transducers, a portable sound-
pressure calibrator (AWA6221A, Hangzhou Aihua In-
struments Co., Ltd., Zhejiang, China) which provided a
normal sound pressure level of 94 dB was used. The gain
of each transducer was then trimmed until the same
value as the normal sound-pressure level was obtained.
The transducers were calibrated at room conditions of
approximately 15 dB. For the frequency-response tests,
however, a sine tone sweeping between 20 Hz and 1000
Hz was delivered to the transducers and the response was
measured using the digital oscilloscope (InstruStar
ISDS205A, Harbin ViMu Electronic Technology Co.,
Ltd., Harbin, China). To accomplish a FFT, the win-
dow-weighting function and range of waveform data that
provided the best results in signal processing were se-
lected. During the recording of heart sounds, the
low-pass Butterworth filter at 1000 Hz was selected.
2.4.2 Measurement of brachial arterial blood pressure
The BABP was measured using a pressure transducer
(Type 4-327-C, Range: 0–400 mmHg, Beckman Instru-
ments Inc., Fullerton, CA, U.S.A.) shown in Figure 2b,
that was situated serially between the proprietary cuff
and commercial blood-pressure appliance (Oberarm-
Blutdruckmessgerät MD 12450, salvatec, Essen, Ger-
many). The appliance corresponds to standards for
non-invasive blood-pressure measuring devices (EN
1060-1:1995+A1:2002 and EN 1060-3:1997+A1:2005).
The pressure transducer and the appliance were cali-
brated occasionally using the reference values provided
by a digital non-invasive sphygmomanometer calibrator
(SLK-BXY-250, Shelok, Shaanxi, China). In an off-line
analysis of the BABP trajectory, the value of the systolic
blood pressure was taken from the trajectory at the point
in which the first BABP oscillation was detected. The
value of the diastolic pressure, however, was taken from
the trajectory at the point at which the oscillation starts
to disappear.
2.4.3 Measurement of forefinger photopleths
To measure the FPPG, a pulse oximeter (Nellcor
N-595, Tyco Healthcare Group LP, Nellcor Puritan
Bennett Division, Pleasanton, CA, U.S.A.) and an adult
SpO2 finger clip attached on the right forefinger (Nellcor
DS-100A, Tyco Healthcare Group LP, Nellcor Puritan
Bennett Division, Pleasanton, CA, U.S.A.) shown in Fig-
ure 2c were used.
2.4.4 Measurement of toe photopleths
To measure the TPPG, a pulse oximeter (Nellcor
N-600, Tyco Healthcare Group LP, Nellcor Puritan
Bennett Division, Pleasanton, CA, U.S.A.) instrumented
with the customized photo-plethysmography foot clip
shown in the Figure 2d was used. For this purpose, an
IR/LED pair and photosensor were removed from the an-
imal ear clip SpO2 sensor (CSL032H, Oximax Animal
Ear Clip SpO2 Sensor for Nellcor N-595, Shenzhen
YKD Technology Co., Ltd., Guangdong, China), was at-
J. ROZMAN et al.: MEASUREMENT OF BASIC HEMODYNAMICS DURING MULTIPOST TRANSCUTANEOUS ...
312 Materiali in tehnologije / Materials and technology 58 (2024) 3, 309–319

tached to the two halves of the tube made of carbon fibre
so to face the lower and upper sides of the toe, respec-
tively. By doing so, a photosensor of the toe clip was ef-
fectively shielded from direct light and the optical path
from IR/LED pair to the photosensor was in an almost
straight line. For the measurements, the foot clip was at-
tached around the left toe.
2.4.5 Measurement of pulsations in brachial artery
To record the blood flow in the brachial artery of the
right arm in the first volunteer, two-dimensional (2-D)
ultrasound mode (B), which uses the echo from solid
structures to display 2-D images of the walls of blood
vessels, was accomplished. For these purposes, the most
advanced portable diagnostic ultrasound device (Venue
Go™ Point of Care Ultrasound, ©GENERAL ELEC-
TRIC COMPANY, U.S.A.), was used before and during
the tANS. The transducer used was a linear array, which
produced an array of parallel, high-frequency ultrasound
while preserving detailed structural definition to a depth
for the superficial brachial artery. The transducer was po-
sitioned along the brachial artery using water-soluble ul-
trasound transmission gel (Ultragel, AquaUltra Basic,
Ultragel Hungary 2000 Ltd., Budapest, Hungary) and
held in place. The position of the transducer was ad-
justed until the clearest picture was obtained. The instru-
ment was then switched automatically to pulse wave
Doppler mode and the mean velocity and cross-sectional
luminal area were measured simultaneously. Accord-
ingly, the diameter of arteries that varied with blood flow
status and over the cardiac cycle, was displayed and re-
corded with motion. Records were then opened using the
VLC media player free software and processed using
ImageJ-win64 software. Processing was performed
within three steps: Extraction of frames at a specific in-
terval opened with VLC software, Image analysis and
Data processing. Results were used to construct dia-
grams showing a train of blood pulses expressed as vein
cross-sectional area over time.
2.4.6 Signal acquisition
All signals obtained from the conditioning circuits
were gathered at 20 kHz with 24-bit resolution using a
high-performance I/O data-acquisition system (DAC)
(DEWE-43a, DEWESOFT d. o. o., Republic of Slo-
venia) as shown schematically in Figure 3. A DAC has
eight differential analogue channel inputs and a USB 2.0
interface. The stimulating intensity i
c
was assessed con-
tinuously by measurement of a voltage drop across the
precision serial resistor of 10Ù in the switching module
connected to the stimulator output. During the acquisi-
tion, each signal was filtered using the low-pass filter
that was selected based on the frequency band of the par-
ticular signal (see legend of Figure 3). Finally, data were
stored on a portable computer (Lenovo W541, Lenovo,
Beijing, China) to permit subsequent frequency analysis
using software (DewesoftX). Figure 3 shows a sche-
matic diagram of the components comprising the system
while the legend below Figure 3 depicts the measured
quantities and filtering applied.
2.4.7 Experimental Procedures
A 45-minute trial was divided into four 5-minute se-
quences where i
C
was delivered separately onto each of
the four posts either at the left or the right EE, respec-
J. ROZMAN et al.: MEASUREMENT OF BASIC HEMODYNAMICS DURING MULTIPOST TRANSCUTANEOUS ...
Materiali in tehnologije / Materials and technology 58 (2024) 3, 309–319 313
Figure 2: Measuring setup: a) Transducers for auscultation of phono-cardiographic signal, b) BABP pressure sensor, c) Forefinger clip SpO2 sen-
sor, d) Customized toe SpO2 sensor

tively. The four sequences were separated with 5-minute
shams where the tANS was not delivered onto any of po-
sitions. The 45-minute trial also started and ended with
the 5-minute sham segment. Quantities i
c
, APCG,
MPCG, FPPG, and TPPG were acquired continuously
throughout the entire trial. The BABP, however, was ac-
quired approximately at the middle of each four 5-min-
ute sequence.
The trials were carried out under the same (and as
steady as possible) conditions with two healthy female
volunteers, age 25 and 28. The subjects were instructed
to avoid stress/tense and physical activity before the trial.
Consumption of alcohol was prohibited before the trial.
Consumption of a large meal later than an hour before
the trial was prohibited. The subjects were asked to lay
supine on the pedicure chair with arms at about heart
level. The subjects were asked not to talk and to remain
as still as possible. Stimulating and all testing positions
were degreased with 70 % isopropyl alcohol and allowed
to dry. The subjects were instructed to relax and rest
their elbows while the BABP cuff was wrapped around
the left arm. Washers were adhered to the transducers.
Transducers were placed at the two standard heart
auscultation posts. A SpO2 clip sensor was attached to
the right forefinger and placed on the left toe. Head-
phones with stimulating plugs were placed onto the
head. The CA was placed on the neck. The intensity i
c
of
the stimuli delivered to the posts LW or RV was set at the
level just below when discomfort was detected. Muscles
in the vicinity of the brachial artery were relaxed so the
mechanical limitation of instantaneous brachial arterial
flow was avoided. The experiment was ended while min-
imizing i
c
and turning the stimulator off. The subjects re-
mained lying supine so stimulating and sensory compo-
nents were removed. The skin at the EE posts and the
skin at the cervical neck was degreased and dried.
2.4.8 Offline Signal Analysis
Offline signal analysis was carried out using a porta-
ble computer (Lenovo W541, Lenovo, Beijing, China)
and the aforementioned software DewesoftX. Any peri-
ods containing motion artefacts that could not be consid-
ered as captured signals were deleted. It was presumed
that some potentially useful information about the state
of the heart valves and arteries during and after tANS,
would likely be obtained from the analysis. The BABP,
FPPG, APCG, MPCG and TPPG, were analysed from
traces during the BABP timeframe just before and just
after the start of the tANS.
3 RESULTS
The results of the assessment are depicted in Figure
4, Figure 5 and Figure 6. Figure 4 depicts the relation-
J. ROZMAN et al.: MEASUREMENT OF BASIC HEMODYNAMICS DURING MULTIPOST TRANSCUTANEOUS ...
314 Materiali in tehnologije / Materials and technology 58 (2024) 3, 309–319
Figure 3: Schematic diagram of the experiment
Legend
Mark Devices and conditions Input Measured Signal Symbol Unit Low Pass/Order
a
Stimulating posts R, Y, B,
W
N/A N/A N/A post N/A
b Stimulating post selector N/A N/A N/A selector N/A
c Common anode N/A N/A N/A anode N/A
d Electrical stimulator 0 tANS intensity ic mA Bessel, 1 kHz, 4th
e Personal computer N/A N/A PC N/A N/A
f
Auscultation transducer at
aortic position
1 Aortic phono-cardiographic APCG dB
Butterworth, 10–300 Hz,
4th
g
Auscultation transducer
at mitral position
4 Mitral phono-cardiographic MPCG dB
Butterworth, 10–300 Hz,
4th
h Acquisition system N/A N/A DAC N/A N/A
i
Pressure transducer at
blood pressure appliance
7
Brachial artery blood pres-
sure
BABP mmHg Bessel, 10 Hz, 4th
j Power Supply Filter N/A N/A N/A N/A N/A
k Pulse oximeter I 9
Forefinger
photo-plethysmographic
FPPG mmHg Bessel, 10Hz, 4th
l Pulse oximeter II 14
Toe
photo-plethysmographic
TPPG mmHg Bessel, 10Hz, 4th
m Isolation transformer N/A N/A N/A N/A N/A

ship between FPPG, TPPG, BABP, APCG and MPCG,
before and during the tANS.
9,21
Precisely, the results are
represented through waveforms of the quantities APCG,
MPCG, BABP, FPPG and TPPG that were recorded in
the second volunteer before and during the tANS of the
post LW located at the bottom of the left EE. Table 1
shows vascular time interval VTT1 elapsed between the
first heart sound S1 and vascular time interval VTT2
elapsed between the second heart sound S2 and systolic
peak in the FPPG signal before the tANS, vascular time
interval VTT3 elapsed between the first heart sound S1
and vascular time interval VTT4 elapsed between the
second heart sound S2 and systolic peak in the FPPG
signal during the tANS. Table I also shows a vascular
time interval VTT1 elapsed between the first heart sound
S1 and vascular time interval VTT2 elapsed between the
second heart sound S2 and systolic peak in the TPPG
signal before the tANS, vascular time interval VTT3
elapsed between the first heart sound S1 and vascular
time interval VTT4 elapsed between the second heart
sound S2 and systolic peak in the TPPG signal during
the tANS.
Similarly, Figure 5 depicts the relationship between
FPPG, TPPG, BABP, APCG and MPCG, before and dur-
ing the tANS.
9
The results are represented through wave-
forms of the quantities APCG, MPCG, BABP, FPPG,
and TPPG that were recorded in the second volunteer be-
fore and during the tANS of the post RW located at the
bottom of the right EE. Table 1 shows vascular time in-
terval VTT1 elapsed between the first heart sound S1
and vascular time interval VTT2 elapsed between the
second heart sound S2 and systolic peak in the FPPG
signal before the tANS, vascular time interval VTT3
elapsed between the first heart sound S1 and vascular
time interval VTT4 elapsed between the second heart
sound S2 and systolic peak in the FPPG signal during the
tANS. Table I also shows a vascular time interval VTT1
elapsed between the first heart sound S1 and vascular
time interval VTT2 elapsed between the second heart
sound S2 and systolic peak in the TPPG signal before the
tANS, vascular time interval VTT3 elapsed between the
first heart sound S1 and vascular time interval VTT4
elapsed between the second heart sound S2 and systolic
peak in the TPPG signal during the tANS.
Figure 6 shows an ultrasound image of pulsing the
right brachial artery indicated with arrows, and a train of
pulsing vein cross-sectional area over time in the first
volunteer. Figure 6a shows the brachial artery pulsing
without tANS, while Figure 6b shows brachial artery
pulsing with tANS of the W post at the left EE. Finally,
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Materiali in tehnologije / Materials and technology 58 (2024) 3, 309–319 315
Figure 4: Relationship between APCG and MPCG, FPPG and TPPG, vascular time interval VTT1 between the first heart sound S1, vascular
time interval VTT2 between the second heart sound S2, and the corresponding systolic peak in the FPPG and TPPG signals before and during
multipost tANS of the LW in the second volunteer. Recorded quantities: a) i
c,
(b) APCG, c) MPCG, d) BABP, s) FPPG, and f) TPPG.

J. ROZMAN et al.: MEASUREMENT OF BASIC HEMODYNAMICS DURING MULTIPOST TRANSCUTANEOUS ...
316 Materiali in tehnologije / Materials and technology 58 (2024) 3, 309–319
Figure 5: Relationship between APCG and MPCG, FPPG and TPPG, vascular time interval (VTT1) between the first heart sound S1, vascular
time interval (VTT2) between the second heart sound S2, and the corresponding systolic peak in the FPPG and TPPG signals before and during
multipost tANS of the RW in the second volunteer. Recorded quantities: a) i
c,
b) APCG, c) MPCG, d) BABP, s) FPPG, and f) TPPG.
Table 1: Vascular time intervals between heart sounds and systolic peaks, heart-sound amplitudes and heart-cycle durations in the second volun-
teer before and during the tANS, respectively.

Figure 6c shows the encircled vein as an important pro-
cessing step of both video recordings.
4 DISCUSSION
In this study we evaluated the effects of multipost
tANS on the dynamics in heart activity and blood flow in
two volunteers during tANS at predefined posts of the
EE and listed potential effects on related hemodynamic
functions. The overall hypothesis of the study was that
the tANS of predefined posts on the left and right EE can
have a measurable effect on heart sounds and some
hemodynamic functions in healthy female volunteers.
The main difference between our study and the stud-
ies of others is that in our study the tANS can be deliv-
ered to posts on the EE via multiple combinations of four
electrodes mounted at predefined positions on a silicone
plug.
22
In addition, optimum working electrochemical
conditions of platinum cathodes used for the tANS were
well defined considering Faradaic reactions as shown in
Section 2.3 tANS set-up. As a result, skin irritation at the
tANS posts was never observed. Furthermore, the charge
density injected by the CE was lower than that injected
by the cathode, so skin irritation stimulating effects were
never observed.
The greatest weakness of the paradigm, however, was
that i
c
density and tANS efficiency were both dependent
predominantly on the pressure produced by the silicone
plug and less on small changes in the position of the plug
within the EE.
23
Furthermore, trials were carried out and
analysed by the same investigator, which might have re-
sulted in some biases. However, the numerical data of
the captured signals based on offline signal analysis
shown in Table 1, minimized subjective interpretation.
The study was intended mainly to obtain initial informa-
tion on the efficiency of the multipost tANS so the num-
ber of subjects tested and measurements performed were
low. Accordingly, the results obtained should be consid-
ered as a basis to gain further research activities that may
result in clinically valuable conclusions. A discussion on
the particular entity measured is presented below.
Body sounds contain important information about
human physiological and psychological conditions.
24
A
non-invasive capture of biomedical signals is relatively
simple and inexpensive; however, body sounds are usu-
ally barely audible. Most contact transducers available
are capable of capturing body sounds that are mainly lo-
cated within the frequency spectrum, ranging from 20 Hz
to 1.3 kHz.
25
Besides, the loudness of captured heart
sounds varies with the auscultation positions.
26
However,
modern biomedical signal-processing techniques are able
to accurately characterize significant features of the heart
sounds contained within the PCGs.
27
With this relation,
the captured S1 and S2 sound can be used to determine
the heart sound type and to detect potentially modified
heart sounds. The amplitude of S1 may provide some
valuable information about myocardial contractility abil-
ity.
28
It was shown that transducers developed enabled a
high-quality auscultation of S1 and S2. The hypothesis
that the tANS has a measurable effect on heart sounds
was confirmed.
An artery of interest for the work was the brachial ar-
tery as the major blood vessel of the upper arm. It was
presumed that tANS can elicit a measurable difference in
the BABP pressure. This hypothesis was not confirmed.
Results showed that vascular time intervals VVT1,
VVT2, VVT3 and VVT4 between heart sounds S1 and
S2, captured as APCG and systolic peaks measured as
FPPG in the second volunteer, were slightly larger dur-
ing the separate tANS of both posts, once for the LW and
once for the RW than before the tANS. It was also shown
that during the tANS of the LW post, heart cycles S1-S1
and S2-S2 contained within the APCG, became slightly
larger and, thus, the heart rhythm became slightly lower.
Besides, they both became slightly louder. During the
tANS of the RW post, however, heart cycles S1-S1 and
S2-S2 contained within the APCG, became slightly
smaller and, thus, the heart rhythm became slightly
higher. Furthermore, S1 became slightly quieter while S2
became slightly louder. The hypothesis that tANS of the
LW and RW has a measurable effect on the forefinger
photopleths was confirmed.
Results showed that vascular time intervals VVT1",
VVT2", VVT3" and VVT4" between heart sounds S1
and S2, captured as MPCG and systolic peaks measured
as TPPG in the second volunteer, were slightly smaller
during the separate tANS of both posts, once for the LW
and once for the RW than before the tANS.
J. ROZMAN et al.: MEASUREMENT OF BASIC HEMODYNAMICS DURING MULTIPOST TRANSCUTANEOUS ...
Materiali in tehnologije / Materials and technology 58 (2024) 3, 309–319 317
Figure 6: Ultrasound image of the right Brachial artery pulsing and
vein cross-sectional area over time in the first volunteer: a) without
tANS, b) with tANS of the RW post, c) Phase of processing

It was also shown that during the tANS of the LW
post, heart cycles S1-S1 and S2-S2 contained within the
MPCG became slightly larger and, thus, the heart rhythm
slightly lower. Besides, both heart sounds S1 and S2 be-
came louder. During the tANS of the RW post, however,
heart cycles S1-S1 and S2-S2 contained within the
MPCG, became slightly smaller and, thus, the heart
rhythm became slightly higher. Furthermore, both, S1
and S2 became slightly quieter. The hypothesis that
tANS of the LW and RW has a measurable effect on the
toe photopleths was confirmed.
The paper details how changes in pulsations of the
brachial artery potentially elicited with the tANS were
obtained using an ultrasound transducer. The exact dy-
namics between the brachial artery pulsations and blood
pressure are actually complex. Namely, blood vessels
have viscoelastic properties that allow the diameter to
vary with a pulsating pressure generated by the left ven-
tricle contractions. It was shown in Figure 6a that the
pattern of the right brachial artery pulsing expressed with
a train of pulsing vein cross-sectional area over time
without tANS, was different to the brachial artery puls-
ing with tANS of the W post at the left EE. It was also
shown that the pattern of the proprietary vein cross-sec-
tional area over time with tANS was different compared
to both the FPPG and TPPG. Accordingly, the hypothe-
sis that tANS has a measurable effect on pulsations in
the brachial artery was confirmed.
Previous studies have indicated that the performance
and autonomic function could be enhanced with the
tANS and that tANS may be a promising treatment for
some neuropsychiatric disorders.
29,30
With this relation
the directions of our future work can include tANS using
a matrix of electrodes and multiple combinations of elec-
trodes to stimulate multiple posts on the EE and fine-tun-
ing of the tANS parameters.
22
5 CONCLUSIONS
It was shown that differences in all vascular time in-
tervals and heart-cycle durations, obtained without tANS
and with tANS of both posts, the LW and RW, were actu-
ally small but were consistent.
It can be concluded that tANS of the LW post elicited
slightly lower heart rate than the one measured when LW
was not stimulated. In contrast, it can be concluded that
the tANS of the RW post elicited a slightly higher heart
rate than the one measured when RW was not stimulated.
Accordingly, the research involving tANS can pro-
mote the method potentially useful to re-establish imbal-
ance or lack of autonomic nervous modulation of heart
valve function. One particular challenge arose from the
study was to determine if valvar motion during diastole
and/or systole is influenced by the innervation that was
modulated by the multipost tANS.
However, to place a methodology into service in a
clinical environment, it should be tested in a larger group
of subjects and trials.
Acknowledgement
The authors wish to acknowledge the Program team
(Research core funding No. P3-0171 by the Slovenian
Research and Innovation agency, Ministry of Higher Ed-
ucation, Science and Innovation, Republic of Slovenia)
at the Institute of Pathophysiology, Faculty of Medicine,
University of Ljubljana, Republic of Slovenia for provid-
ing language help, writing assistance, proof reading the
article and editing the manuscript.
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