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Fundamentals and Applications of Fluid Mechanics and Acoustics in Biomedical Engineering

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A special issue of Bioengineering (ISSN 2306-5354).

Deadline for manuscript submissions: closed (1 September 2023) | Viewed by 24583

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Prof. Dr. Ephraim Gutmark

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Guest Editor

Ohio Regents Eminent Scholar, University of Cincinnati, Cincinnati, OH 45221-0070, USA
Interests: computational biomedical engineering; Computational Fluid Dynamics (CFD); Flow-Structure Interaction (FSI); biomedical measurement techniques; respiratory system; voice; hemodynamics; medical devices
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Dr. Iris Little

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Guest Editor

Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229, USA
Interests: computational methods to assess pathophysiology of aortic and airway disease; turner syndrome; growth disorders; pubertal disorders
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Special Issue Information

Dear Colleagues,

The field of biomedical engineering has recently experienced important advances in experimental, computational, and analytical research in fluid mechanics as well as acoustics. New imaging modalities, advanced instrumentation, and efficient computational methodologies have enabled these advances. The findings contribute to a better understanding of physiological processes in the circulatory and respiratory systems, as well as phonation, and have already led to new therapies that will promote better human health. The early diagnosis of diseases, monitoring of their progression, patient-specific treatments, surgical planning, and new medical devices are some examples of these transformative achievements.

This Special Issue will focus on original research papers on and comprehensive reviews of the “Fundamentals and Novel Applications of Fluid Mechanics and Acoustics in Biomedical Engineering”. It will highlight recent developments in these areas and encourage further scientific contributions and discussions. Topics of interest for this Special Issue include, but are not limited to, the following:

General Topics
1. Advanced computational biomechanical applications, such as computational fluid dynamics, flow–structure interaction, and the immerse boundary method.
2. Innovative experimental and imaging techniques in bioflows and bioacoustics relevant to the human body.
3. Device development and translational technology.
Hemodynamics
1. Multiscale and multiphysics modeling of the cardiovascular system.
2. Cardiovascular imaging (flow, wall motion, and impact on tissue).
3. Experiments on and modeling of cardiovascular and cerebral blood flow.
4. Medical devices, valvular dynamics, and wave propagation.
Respiratory system
1. Airway collapsibility in obstructive sleep apnea (OSA).
2. Nasal and oral breathing.
3. Airway resistance and Starling resistor.
Voice and Speech Production, and General Acoustics
1. Aerodynamics of voice production.
2. Biomechanics of the larynx and interaction with flow.
3. Acoustics-based diagnostics of medical conditions.

Prof. Dr. Ephraim Gutmark
Dr. Iris Little
Guest Editors

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Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Bioengineering is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

hemodynamics
cardiovascular flow
sleep apnea
airway
voice
bioacoustics
CFD
FSI
bioflows

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Fundamentals and Novel Applications of Fluid Mechanics, Biomechanics, and Acoustics in Biomedical Engineering, 2nd Edition in Bioengineering

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Editorial

Jump to: Research, Review

4 pages, 158 KiB

Open AccessEditorial

Fundamentals and Applications of Fluid Mechanics and Acoustics in Biomedical Engineering

by Iris Little and Ephraim Gutmark

Bioengineering 2024, 11(11), 1125; https://doi.org/10.3390/bioengineering11111125 - 8 Nov 2024

Viewed by 626

Abstract

The field of biomedical engineering has experienced important recent advances in experimental, computational, and analytical research in fluid mechanics and acoustics [...] Full article

(This article belongs to the Special Issue Fundamentals and Applications of Fluid Mechanics and Acoustics in Biomedical Engineering)

Research

Jump to: Editorial, Review

19 pages, 8415 KiB

Open AccessArticle

Modeling Anisotropic Electrical Conductivity of Blood: Translating Microscale Effects of Red Blood Cell Motion into a Macroscale Property of Blood

by Alireza Jafarinia, Vahid Badeli, Thomas Krispel, Gian Marco Melito, Günter Brenn, Alice Reinbacher-Köstinger, Manfred Kaltenbacher and Thomas Hochrainer

Bioengineering 2024, 11(2), 147; https://doi.org/10.3390/bioengineering11020147 - 1 Feb 2024

Cited by 1 | Viewed by 1806

Abstract

Cardiovascular diseases are a leading global cause of mortality. The current standard diagnostic methods, such as imaging and invasive procedures, are relatively expensive and partly connected with risks to the patient. Bioimpedance measurements hold the promise to offer rapid, safe, and low-cost alternative diagnostic methods. In the realm of cardiovascular diseases, bioimpedance methods rely on the changing electrical conductivity of blood, which depends on the local hemodynamics. However, the exact dependence of blood conductivity on the hemodynamic parameters is not yet fully understood, and the existing models for this dependence are limited to rather academic flow fields in straight pipes or channels. In this work, we suggest two closely connected anisotropic electrical conductivity models for blood in general three-dimensional flows, which consider the orientation and alignment of red blood cells (RBCs) in shear flows. In shear flows, RBCs adopt preferred orientations through a rotation of their membrane known as tank-treading motion. The two models are built on two different assumptions as to which hemodynamic characteristic determines the preferred orientation. The models are evaluated in two example simulations of blood flow. In a straight rigid vessel, the models coincide and are in accordance with experimental observations. In a simplified aorta geometry, the models yield different results. These differences are analyzed quantitatively, but a validation of the models with experiments is yet outstanding. Full article

(This article belongs to the Special Issue Fundamentals and Applications of Fluid Mechanics and Acoustics in Biomedical Engineering)

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18 pages, 3753 KiB

Open AccessArticle

Vibro-Acoustic Platelet Activation: An Additive Mechanism of Prothrombosis with Applicability to Snoring and Obstructive Sleep Apnea

by Daniel E. Palomares, Phat L. Tran, Catherine Jerman, Moe Momayez, Pierre Deymier, Jawaad Sheriff, Danny Bluestein, Sairam Parthasarathy and Marvin J. Slepian

Bioengineering 2023, 10(12), 1414; https://doi.org/10.3390/bioengineering10121414 - 12 Dec 2023

Cited by 1 | Viewed by 1652

Abstract

Introduction: Obstructive sleep apnea (OSA) and loud snoring are conditions with increased cardiovascular risk and notably an association with stroke. Central in stroke are thrombosis and thromboembolism, all related to and initiaing with platelet activation. Platelet activation in OSA has been felt to be driven by biochemical and inflammatory means, including intermittent catecholamine exposure and transient hypoxia. We hypothesized that snore-associated acoustic vibration (SAAV) is an activator of platelets that synergizes with catecholamines and hypoxia to further amplify platelet activation. Methods: Gel-filtered human platelets were exposed to snoring utilizing a designed vibro-acoustic exposure device, varying the time and intensity of exposure and frequency content. Platelet activation was assessed via thrombin generation using the Platelet Activity State assay and scanning electron microscopy. Comparative activation induced by epinephrine and hypoxia were assessed individually as well as additively with SAAV, as well as the inhibitory effect of aspirin. Results: We demonstrate that snore-associated acoustic vibration is an independent activator of platelets, which is dependent upon the dose of exposure, i.e., intensity x time. In snoring, acoustic vibrations associated with low-frequency sound content (200 Hz) are more activating than those associated with high frequencies (900 Hz) (53.05% vs. 22.08%, p = 0.001). Furthermore, SAAV is additive to both catecholamines and hypoxia-mediated activation, inducing synergistic activation. Finally, aspirin, a known inhibitor of platelet activation, has no significant effect in limiting SAAV platelet activation. Conclusion: Snore-associated acoustic vibration is a mechanical means of platelet activation, which may drive prothrombosis and thrombotic risk clinically observed in loud snoring and OSA. Full article

(This article belongs to the Special Issue Fundamentals and Applications of Fluid Mechanics and Acoustics in Biomedical Engineering)

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21 pages, 9934 KiB

Open AccessArticle

On the Alignment of Acoustic and Coupled Mechanic-Acoustic Eigenmodes in Phonation by Supraglottal Duct Variations

by Florian Kraxberger, Christoph Näger, Marco Laudato, Elias Sundström, Stefan Becker, Mihai Mihaescu, Stefan Kniesburges and Stefan Schoder

Bioengineering 2023, 10(12), 1369; https://doi.org/10.3390/bioengineering10121369 - 28 Nov 2023

Cited by 5 | Viewed by 1177

Abstract

Sound generation in human phonation and the underlying fluid–structure–acoustic interaction that describes the sound production mechanism are not fully understood. A previous experimental study, with a silicone made vocal fold model connected to a straight vocal tract pipe of fixed length, showed that vibroacoustic coupling can cause a deviation in the vocal fold vibration frequency. This occurred when the fundamental frequency of the vocal fold motion was close to the lowest acoustic resonance frequency of the pipe. What is not fully understood is how the vibroacoustic coupling is influenced by a varying vocal tract length. Presuming that this effect is a pure coupling of the acoustical effects, a numerical simulation model is established based on the computation of the mechanical-acoustic eigenvalue. With varying pipe lengths, the lowest acoustic resonance frequency was adjusted in the experiments and so in the simulation setup. In doing so, the evolution of the vocal folds’ coupled eigenvalues and eigenmodes is investigated, which confirms the experimental findings. Finally, it was shown that for normal phonation conditions, the mechanical mode is the most efficient vibration pattern whenever the acoustic resonance of the pipe (lowest formant) is far away from the vocal folds’ vibration frequency. Whenever the lowest formant is slightly lower than the mechanical vocal fold eigenfrequency, the coupled vocal fold motion pattern at the formant frequency dominates. Full article

(This article belongs to the Special Issue Fundamentals and Applications of Fluid Mechanics and Acoustics in Biomedical Engineering)

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18 pages, 24683 KiB

Open AccessArticle

An Investigation of Acoustic Back-Coupling in Human Phonation on a Synthetic Larynx Model

by Christoph Näger, Stefan Kniesburges, Bogac Tur, Stefan Schoder and Stefan Becker

Bioengineering 2023, 10(12), 1343; https://doi.org/10.3390/bioengineering10121343 - 22 Nov 2023

Cited by 4 | Viewed by 1274

Abstract

In the human phonation process, acoustic standing waves in the vocal tract can influence the fluid flow through the glottis as well as vocal fold oscillation. To investigate the amount of acoustic back-coupling, the supraglottal flow field has been recorded via high-speed particle image velocimetry (PIV) in a synthetic larynx model for several configurations with different vocal tract lengths. Based on the obtained velocity fields, acoustic source terms were computed. Additionally, the sound radiation into the far field was recorded via microphone measurements and the vocal fold oscillation via high-speed camera recordings. The PIV measurements revealed that near a vocal tract resonance frequency f_R, the vocal fold oscillation frequency f_o (and therefore also the flow field’s fundamental frequency) jumps onto f_R. This is accompanied by a substantial relative increase in aeroacoustic sound generation efficiency. Furthermore, the measurements show that f_o-f_R-coupling increases vocal efficiency, signal-to-noise ratio, harmonics-to-noise ratio and cepstral peak prominence. At the same time, the glottal volume flow needed for stable vocal fold oscillation decreases strongly. All of this results in an improved voice quality and phonation efficiency so that a person phonating with f_o-f_R-coupling can phonate longer and with better voice quality. Full article

(This article belongs to the Special Issue Fundamentals and Applications of Fluid Mechanics and Acoustics in Biomedical Engineering)

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23 pages, 3813 KiB

Open AccessArticle

Time-Dependent Fluid-Structure Interaction Simulations of a Simplified Human Soft Palate

by Peng Li, Marco Laudato and Mihai Mihaescu

Bioengineering 2023, 10(11), 1313; https://doi.org/10.3390/bioengineering10111313 - 14 Nov 2023

Cited by 2 | Viewed by 1327

Abstract

Obstructive Sleep Apnea Syndrome (OSAS) is a common sleep-related disorder. It is characterized by recurrent partial or total collapse of pharyngeal upper airway accompanied by induced vibrations of the soft tissues (e.g., soft palate). The knowledge of the tissue behavior subject to a particular airflow is relevant for realistic clinic applications. However, in-vivo measurements are usually impractical. The goal of the present study is to develop a 3D fluid-structure interaction model for the human uvulopalatal system relevant to OSA based on simplified geometries under physiological conditions. Numerical simulations are performed to assess the influence of the different breathing conditions on the vibrational dynamics of the flexible structure. Meanwhile, the fluid patterns are investigated for the coupled fluid-structure system as well. Increasing the respiratory flow rate is shown to induce larger structural deformation. Vortex shedding induced resonance is not observed due to the large discrepancy between the flow oscillatory frequency and the natural frequency of the structure. The large deformation for symmetric breathing case under intensive respiration is mainly because of the positive feedback from the pressure differences on the top and the bottom surfaces of the structure. Full article

(This article belongs to the Special Issue Fundamentals and Applications of Fluid Mechanics and Acoustics in Biomedical Engineering)

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20 pages, 3882 KiB

Open AccessArticle

Assessment of Rheological Models Applied to Blood Flow in Human Thoracic Aorta

by Alexander Fuchs, Niclas Berg, Laszlo Fuchs and Lisa Prahl Wittberg

Bioengineering 2023, 10(11), 1240; https://doi.org/10.3390/bioengineering10111240 - 24 Oct 2023

Cited by 5 | Viewed by 1555

Abstract

Purpose: The purpose of this study is to assess the importance of non-Newtonian rheological models on blood flow in the human thoracic aorta. Methods: The pulsatile flow in the aorta is simulated using the models of Casson, Quemada and Walburn–Schneck in addition to a case of fixed (Newtonian) viscosity. The impact of the four rheological models (using constant hematocrit) was assessed with respect to (i) magnitude and deviation of the viscosity relative to a reference value (the Newtonian case); (ii) wall shear stress (WSS) and its time derivative; (iii) common WSS-related indicators, OSI, TAWSS and RRT; (iv) relative volume and surface-based retrograde flow; and (v) the impact of rheological models on the transport of small particles in the thoracic aorta. Results: The time-dependent flow in the thoracic aorta implies relatively large variations in the instantaneous WSS, due to variations in the instantaneous viscosity by as much as an order of magnitude. The largest effect was observed for low shear rates (tens s⁻¹). The different viscosity models had a small impact in terms of time- and spaced-averaged quantities. The significance of the rheological models was clearly demonstrated in the instantaneous WSS, for the space-averaged WSS (about 10%) and the corresponding temporal derivative of WSS (up to 20%). The longer-term accumulated effect of the rheological model was observed for the transport of spherical particles of 2 mm and 2 mm in diameter (density of 1200 kg/m³). Large particles’ total residence time in the brachiocephalic artery was 60% longer compared to the smaller particles. For the left common carotid artery, the opposite was observed: the smaller particles resided considerably longer than their larger counterparts. Conclusions: The dependence on the non-Newtonian properties of blood is mostly important at low shear regions (near walls, stagnation regions). Time- and space-averaging parameters of interest reduce the impact of the rheological model and may thereby lead to under-estimation of viscous effects. The rheological model affects the local WSS and its temporal derivative. In addition, the transport of small particles includes the accumulated effect of the blood rheological model as the several forces (e.g., drag, added mass and lift) acting on the particles are viscosity dependent. Mass transport is an essential factor for the development of pathologies in the arterial wall, implying that rheological models are important for assessing such risks. Full article

(This article belongs to the Special Issue Fundamentals and Applications of Fluid Mechanics and Acoustics in Biomedical Engineering)

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14 pages, 24344 KiB

Open AccessArticle

Impact of Variation in Commissural Angle between Fused Leaflets in the Functionally Bicuspid Aortic Valve on Hemodynamics and Tissue Biomechanics

by Elias Sundström and Justin T. Tretter

Bioengineering 2023, 10(10), 1219; https://doi.org/10.3390/bioengineering10101219 - 18 Oct 2023

Cited by 5 | Viewed by 2186

Abstract

In subjects with functionally bicuspid aortic valves (BAVs) with fusion between the coronary leaflets, there is a natural variation of the commissural angle. What is not fully understood is how this variation influences the hemodynamics and tissue biomechanics. These variables may influence valvar durability and function, both in the native valve and following repair, and influence ongoing aortic dilation. A 3D aortic valvar model was reconstructed from a patient with a normal trileaflet aortic valve using cardiac magnetic resonance (CMR) imaging. Fluid–structure interaction (FSI) simulations were used to compare the effects of the varying commissural angles between the non-coronary with its adjacent coronary leaflet. The results showed that the BAV with very asymmetric commissures (

120^{\circ}

degree commissural angle) reduces the aortic opening area during peak systole and with a jet that impacts on the right posterior wall proximally of the ascending aorta, giving rise to elevated wall shear stress. This manifests in a shear layer with a retrograde flow and strong swirling towards the fused leaflet side. In contrast, a more symmetrical commissural angle (

180^{\circ}

degree commissural angle) reduces the jet impact on the posterior wall and leads to a linear decrease in stress and strain levels in the non-fused non-coronary leaflet. These findings highlight the importance of considering the commissural angle in the progression of aortic valvar stenosis, the regional distribution of stresses and strain levels experienced by the leaflets which may predispose to valvar deterioration, and progression in thoracic aortic dilation in patients with functionally bicuspid aortic valves. Understanding the hemodynamics and biomechanics of the functionally bicuspid aortic valve and its variation in structure may provide insight into predicting the risk of aortic valve dysfunction and thoracic aortic dilation, which could inform clinical decision making and potentially lead to improved aortic valvar surgical outcomes. Full article

(This article belongs to the Special Issue Fundamentals and Applications of Fluid Mechanics and Acoustics in Biomedical Engineering)

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15 pages, 10190 KiB

Open AccessArticle

Machine Learning-Based Segmentation of the Thoracic Aorta with Congenital Valve Disease Using MRI

by Elias Sundström and Marco Laudato

Bioengineering 2023, 10(10), 1216; https://doi.org/10.3390/bioengineering10101216 - 18 Oct 2023

Cited by 5 | Viewed by 2369

Abstract

Subjects with bicuspid aortic valves (BAV) are at risk of developing valve dysfunction and need regular clinical imaging surveillance. Management of BAV involves manual and time-consuming segmentation of the aorta for assessing left ventricular function, jet velocity, gradient, shear stress, and valve area with aortic valve stenosis. This paper aims to employ machine learning-based (ML) segmentation as a potential for improved BAV assessment and reducing manual bias. The focus is on quantifying the relationship between valve morphology and vortical structures, and analyzing how valve morphology influences the aorta’s susceptibility to shear stress that may lead to valve incompetence. The ML-based segmentation that is employed is trained on whole-body Computed Tomography (CT). Magnetic Resonance Imaging (MRI) is acquired from six subjects, three with tricuspid aortic valves (TAV) and three functionally BAV, with right–left leaflet fusion. These are used for segmentation of the cardiovascular system and delineation of four-dimensional phase-contrast magnetic resonance imaging (4D-PCMRI) for quantification of vortical structures and wall shear stress. The ML-based segmentation model exhibits a high Dice score (0.86) for the heart organ, indicating a robust segmentation. However, the Dice score for the thoracic aorta is comparatively poor (0.72). It is found that wall shear stress is predominantly symmetric in TAVs. BAVs exhibit highly asymmetric wall shear stress, with the region opposite the fused coronary leaflets experiencing elevated tangential wall shear stress. This is due to the higher tangential velocity explained by helical flow, proximally of the sinutubal junction of the ascending aorta. ML-based segmentation not only reduces the runtime of assessing the hemodynamic effectiveness, but also identifies the significance of the tangential wall shear stress in addition to the axial wall shear stress that may lead to the progression of valve incompetence in BAVs, which could guide potential adjustments in surgical interventions. Full article

(This article belongs to the Special Issue Fundamentals and Applications of Fluid Mechanics and Acoustics in Biomedical Engineering)

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14 pages, 2665 KiB

Open AccessArticle

The Effects of Negative Pressure Induced by Flow Separation Vortices on Vocal Fold Dynamics during Voice Production

by Weili Jiang, Xudong Zheng, Charles Farbos de Luzan, Liran Oren, Ephraim Gutmark and Qian Xue

Bioengineering 2023, 10(10), 1215; https://doi.org/10.3390/bioengineering10101215 - 18 Oct 2023

Cited by 2 | Viewed by 1357

Abstract

This study used a two-dimensional flow-structure-interaction computer model to investigate the effects of flow-separation-vortex-induced negative pressure on vocal fold vibration and flow dynamics during vocal fold vibration. The study found that negative pressure induced by flow separation vortices enhances vocal fold vibration by increasing aeroelastic energy transfer during vibration. The result showed that the intraglottal pressure was predominantly negative after flow separation before gradually recovering to zero at the glottis exit. When the negative pressure was removed, the vibration amplitude and flow rate were reduced by up to 20%, and the closing speed, flow skewness quotient, and maximum flow declination rate were reduced by up to 40%. The study provides insights into the complex interactions between flow dynamics, vocal fold vibration, and energy transfer during voice production. Full article

(This article belongs to the Special Issue Fundamentals and Applications of Fluid Mechanics and Acoustics in Biomedical Engineering)

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12 pages, 24354 KiB

Open AccessArticle

Blood Speckle Imaging: An Emerging Method for Perioperative Evaluation of Subaortic and Aortic Valvar Repair

by Elias Sundström, Michael Jiang, Hani K. Najm and Justin T. Tretter

Bioengineering 2023, 10(10), 1183; https://doi.org/10.3390/bioengineering10101183 - 12 Oct 2023

Cited by 3 | Viewed by 2205

Abstract

Background: This article presents the use of blood speckle Imaging (BSI) as an echocardiographic approach for the pre- and post-operative evaluation of subaortic membrane resection and aortic valve repair. Method: BSI, employing block-matching algorithms, provided detailed visualization of flow patterns and quantification of parameters from ultrasound data. The 9-year-old patient underwent subaortic membrane resection and peeling extensions of the membrane from under the ventricular-facing surface of all three aortic valve leaflets. Result: Post-operatively, BSI demonstrated improvements in hemodynamic patterns, where quantified changes in flow velocities showed no signs of stenosis and trivial regurgitation. The asymmetric jet with a shear layer and flow reversal on the posterior aspect of the aorta was corrected resulting in reduced wall shear stress on the anterior aspect and reduced oscillatory shear index, which is considered a contributing element in cellular alterations in the structure of the aortic wall. Conclusion: This proof-of-concept study demonstrates the potential of BSI as an emerging echocardiographic approach for evaluating subaortic and aortic valvar repair. BSI enhances the quantitative evaluation of the left ventricular outflow tract of immediate surgical outcomes beyond traditional echocardiographic parameters and aids in post-operative decision-making. However, larger studies are needed to validate these findings and establish standardized protocols for clinical implementation. Full article

(This article belongs to the Special Issue Fundamentals and Applications of Fluid Mechanics and Acoustics in Biomedical Engineering)

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19 pages, 4440 KiB

Open AccessArticle

Effect of Ligament Fibers on Dynamics of Synthetic, Self-Oscillating Vocal Folds in a Biomimetic Larynx Model

by Bogac Tur, Lucia Gühring, Olaf Wendler, Samuel Schlicht, Dietmar Drummer and Stefan Kniesburges

Bioengineering 2023, 10(10), 1130; https://doi.org/10.3390/bioengineering10101130 - 26 Sep 2023

Cited by 6 | Viewed by 1563

Abstract

Synthetic silicone larynx models are essential for understanding the biomechanics of physiological and pathological vocal fold vibrations. The aim of this study is to investigate the effects of artificial ligament fibers on vocal fold vibrations in a synthetic larynx model, which is capable of replicating physiological laryngeal functions such as elongation, abduction, and adduction. A multi-layer silicone model with different mechanical properties for the musculus vocalis and the lamina propria consisting of ligament and mucosa was used. Ligament fibers of various diameters and break resistances were cast into the vocal folds and tested at different tension levels. An electromechanical setup was developed to mimic laryngeal physiology. The measurements included high-speed video recordings of vocal fold vibrations, subglottal pressure and acoustic. For the evaluation of the vibration characteristics, all measured values were evaluated and compared with parameters from ex and in vivo studies. The fundamental frequency of the synthetic larynx model was found to be approximately 200–520 Hz depending on integrated fiber types and tension levels. This range of the fundamental frequency corresponds to the reproduction of a female normal and singing voice range. The investigated voice parameters from vocal fold vibration, acoustics, and subglottal pressure were within normal value ranges from ex and in vivo studies. The integration of ligament fibers leads to an increase in the fundamental frequency with increasing airflow, while the tensioning of the ligament fibers remains constant. In addition, a tension increase in the fibers also generates a rise in the fundamental frequency delivering the physiological expectation of the dynamic behavior of vocal folds. Full article

(This article belongs to the Special Issue Fundamentals and Applications of Fluid Mechanics and Acoustics in Biomedical Engineering)

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22 pages, 4730 KiB

Open AccessArticle

Vortical Structures Promote Atheroprotective Wall Shear Stress Distributions in a Carotid Artery Bifurcation Model

by Nora C. Wild, Kartik V. Bulusu and Michael W. Plesniak

Bioengineering 2023, 10(9), 1036; https://doi.org/10.3390/bioengineering10091036 - 3 Sep 2023

Cited by 6 | Viewed by 1922

Abstract

Carotid artery diseases, such as atherosclerosis, are a major cause of death in the United States. Wall shear stresses are known to prompt plaque formation, but there is limited understanding of the complex flow structures underlying these stresses and how they differ in a pre-disposed high-risk patient cohort. A ‘healthy’ and a novel ‘pre-disposed’ carotid artery bifurcation model was determined based on patient-averaged clinical data, where the ‘pre-disposed’ model represents a pathological anatomy. Computational fluid dynamic simulations were performed using a physiological flow based on healthy human subjects. A main hairpin vortical structure in the internal carotid artery sinus was observed, which locally increased instantaneous wall shear stress. In the pre-disposed geometry, this vortical structure starts at an earlier instance in the cardiac flow cycle and persists over a much shorter period, where the second half of the cardiac cycle is dominated by perturbed secondary flow structures and vortices. This coincides with weaker favorable axial pressure gradient peaks over the sinus for the ‘pre-disposed’ geometry. The findings reveal a strong correlation between vortical structures and wall shear stress and imply that an intact internal carotid artery sinus hairpin vortical structure has a physiologically beneficial role by increasing local wall shear stresses. The deterioration of this beneficial vortical structure is expected to play a significant role in atherosclerotic plaque formation. Full article

(This article belongs to the Special Issue Fundamentals and Applications of Fluid Mechanics and Acoustics in Biomedical Engineering)

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Review

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86 pages, 41113 KiB

Open AccessReview

Computational Rhinology: Unraveling Discrepancies between In Silico and In Vivo Nasal Airflow Assessments for Enhanced Clinical Decision Support

by Sverre Gullikstad Johnsen

Bioengineering 2024, 11(3), 239; https://doi.org/10.3390/bioengineering11030239 - 28 Feb 2024

Cited by 2 | Viewed by 1703

Abstract

Computational rhinology is a specialized branch of biomechanics leveraging engineering techniques for mathematical modelling and simulation to complement the medical field of rhinology. Computational rhinology has already contributed significantly to advancing our understanding of the nasal function, including airflow patterns, mucosal cooling, particle deposition, and drug delivery, and is foreseen as a crucial element in, e.g., the development of virtual surgery as a clinical, patient-specific decision support tool. The current paper delves into the field of computational rhinology from a nasal airflow perspective, highlighting the use of computational fluid dynamics to enhance diagnostics and treatment of breathing disorders. This paper consists of three distinct parts—an introduction to and review of the field of computational rhinology, a review of the published literature on in vitro and in silico studies of nasal airflow, and the presentation and analysis of previously unpublished high-fidelity CFD simulation data of in silico rhinomanometry. While the two first parts of this paper summarize the current status and challenges in the application of computational tools in rhinology, the last part addresses the gross disagreement commonly observed when comparing in silico and in vivo rhinomanometry results. It is concluded that this discrepancy cannot readily be explained by CFD model deficiencies caused by poor choice of turbulence model, insufficient spatial or temporal resolution, or neglecting transient effects. Hence, alternative explanations such as nasal cavity compliance or drag effects due to nasal hair should be investigated. Full article

(This article belongs to the Special Issue Fundamentals and Applications of Fluid Mechanics and Acoustics in Biomedical Engineering)

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