Abstract

Background Despite the evolution of Ventricular Assist Devices (VADs), VAD patients still suffer from complications, often due to damage to the blood by fluid dynamic stress. To date, most numerical models for blood damage are functions of the scalar shear stress (SSS), the second invariant of the strain rate. Since rotary VADs are assumed to exert mainly shear stress, the measurements of blood damage for these models are obtained from shear flow experiments. However, measurements of cell deformation show elongational and shear stress deform cells differently, and then potentially damage cells differently. Aim The aim of this work was to use computational fluid dynamics (CFD) to assess the significance of elongational stress, in comparison with shear stress, in rotary VADs.MethodsCFD was used to calculate flow fields in a centrifugal and an axial VAD. The velocity of the blood defined the reference frame, with both stresses computed from the transformed strain rate. Firstly, volumes of the VADs experiencing shear or elongational stress above threshold values were found. And secondly, the cell deformation index (DI= (L-W)/ (L+W); given the cell’s length, L, and width, W) was set to 0.5, and the regions of the VADs producing DI > 0.5 due to shear or elongation stress were compared.Results Compared with elongation stress, blood in the VADs experiences higher shear stress over a larger volume. However, when comparing the stress using a threshold value for cell deformation, elongational stress occurs in a smaller but significant volume of both VADs (significant elongational stress volumes: centrifugal 0.2 cm3, axial 0.15 cm3, compared with significant shear stress volumes: centrifugal 0.3 cm3, axial 0.5 cm3). Conclusion Although shear stress volumes are larger than elongational volumes for both VADs, the latter are still significant in size. Crucially, given that the axial design reduces the significant elongational stress volume, but increases that for shear stress, more experimental data is needed on elongational stress-induced damage, with which to inform the design of new VADs.
LanguageEnglish
Pages405 - 405
Number of pages1
JournalThe International Journal of Artificial Organs
Volume40
Issue number8
StatusPublished - 6 Sep 2017
Event44th ESAO and 7th IFAO Congress, 2017, Vienna - Vienna, Austria
Duration: 6 Sep 20179 Sep 2017

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Heart-Assist Devices
Shear stress
Blood
Hydrodynamics
Strain rate
Elongation
Shear flow
Fluid dynamics
Numerical models
Flow fields
Computational fluid dynamics

Cite this

@article{6f7cb35c2060495398c3b3d2bdfe83dc,
title = "Numerical Comparison of Shear and Elongational Stresses in Rotary Ventricular Assist Devices",
abstract = "Background Despite the evolution of Ventricular Assist Devices (VADs), VAD patients still suffer from complications, often due to damage to the blood by fluid dynamic stress. To date, most numerical models for blood damage are functions of the scalar shear stress (SSS), the second invariant of the strain rate. Since rotary VADs are assumed to exert mainly shear stress, the measurements of blood damage for these models are obtained from shear flow experiments. However, measurements of cell deformation show elongational and shear stress deform cells differently, and then potentially damage cells differently. Aim The aim of this work was to use computational fluid dynamics (CFD) to assess the significance of elongational stress, in comparison with shear stress, in rotary VADs.MethodsCFD was used to calculate flow fields in a centrifugal and an axial VAD. The velocity of the blood defined the reference frame, with both stresses computed from the transformed strain rate. Firstly, volumes of the VADs experiencing shear or elongational stress above threshold values were found. And secondly, the cell deformation index (DI= (L-W)/ (L+W); given the cell’s length, L, and width, W) was set to 0.5, and the regions of the VADs producing DI > 0.5 due to shear or elongation stress were compared.Results Compared with elongation stress, blood in the VADs experiences higher shear stress over a larger volume. However, when comparing the stress using a threshold value for cell deformation, elongational stress occurs in a smaller but significant volume of both VADs (significant elongational stress volumes: centrifugal 0.2 cm3, axial 0.15 cm3, compared with significant shear stress volumes: centrifugal 0.3 cm3, axial 0.5 cm3). Conclusion Although shear stress volumes are larger than elongational volumes for both VADs, the latter are still significant in size. Crucially, given that the axial design reduces the significant elongational stress volume, but increases that for shear stress, more experimental data is needed on elongational stress-induced damage, with which to inform the design of new VADs.",
author = "Khoo, {Dominica Pi Ying} and Harinderjit Gill and Andrew Cookson and Katharine Fraser",
year = "2017",
month = "9",
day = "6",
language = "English",
volume = "40",
pages = "405 -- 405",
journal = "The International Journal of Artificial Organs",
issn = "0391-3988",
publisher = "Wichtig Publishing",
number = "8",

}

TY - JOUR

T1 - Numerical Comparison of Shear and Elongational Stresses in Rotary Ventricular Assist Devices

AU - Khoo, Dominica Pi Ying

AU - Gill, Harinderjit

AU - Cookson, Andrew

AU - Fraser, Katharine

PY - 2017/9/6

Y1 - 2017/9/6

N2 - Background Despite the evolution of Ventricular Assist Devices (VADs), VAD patients still suffer from complications, often due to damage to the blood by fluid dynamic stress. To date, most numerical models for blood damage are functions of the scalar shear stress (SSS), the second invariant of the strain rate. Since rotary VADs are assumed to exert mainly shear stress, the measurements of blood damage for these models are obtained from shear flow experiments. However, measurements of cell deformation show elongational and shear stress deform cells differently, and then potentially damage cells differently. Aim The aim of this work was to use computational fluid dynamics (CFD) to assess the significance of elongational stress, in comparison with shear stress, in rotary VADs.MethodsCFD was used to calculate flow fields in a centrifugal and an axial VAD. The velocity of the blood defined the reference frame, with both stresses computed from the transformed strain rate. Firstly, volumes of the VADs experiencing shear or elongational stress above threshold values were found. And secondly, the cell deformation index (DI= (L-W)/ (L+W); given the cell’s length, L, and width, W) was set to 0.5, and the regions of the VADs producing DI > 0.5 due to shear or elongation stress were compared.Results Compared with elongation stress, blood in the VADs experiences higher shear stress over a larger volume. However, when comparing the stress using a threshold value for cell deformation, elongational stress occurs in a smaller but significant volume of both VADs (significant elongational stress volumes: centrifugal 0.2 cm3, axial 0.15 cm3, compared with significant shear stress volumes: centrifugal 0.3 cm3, axial 0.5 cm3). Conclusion Although shear stress volumes are larger than elongational volumes for both VADs, the latter are still significant in size. Crucially, given that the axial design reduces the significant elongational stress volume, but increases that for shear stress, more experimental data is needed on elongational stress-induced damage, with which to inform the design of new VADs.

AB - Background Despite the evolution of Ventricular Assist Devices (VADs), VAD patients still suffer from complications, often due to damage to the blood by fluid dynamic stress. To date, most numerical models for blood damage are functions of the scalar shear stress (SSS), the second invariant of the strain rate. Since rotary VADs are assumed to exert mainly shear stress, the measurements of blood damage for these models are obtained from shear flow experiments. However, measurements of cell deformation show elongational and shear stress deform cells differently, and then potentially damage cells differently. Aim The aim of this work was to use computational fluid dynamics (CFD) to assess the significance of elongational stress, in comparison with shear stress, in rotary VADs.MethodsCFD was used to calculate flow fields in a centrifugal and an axial VAD. The velocity of the blood defined the reference frame, with both stresses computed from the transformed strain rate. Firstly, volumes of the VADs experiencing shear or elongational stress above threshold values were found. And secondly, the cell deformation index (DI= (L-W)/ (L+W); given the cell’s length, L, and width, W) was set to 0.5, and the regions of the VADs producing DI > 0.5 due to shear or elongation stress were compared.Results Compared with elongation stress, blood in the VADs experiences higher shear stress over a larger volume. However, when comparing the stress using a threshold value for cell deformation, elongational stress occurs in a smaller but significant volume of both VADs (significant elongational stress volumes: centrifugal 0.2 cm3, axial 0.15 cm3, compared with significant shear stress volumes: centrifugal 0.3 cm3, axial 0.5 cm3). Conclusion Although shear stress volumes are larger than elongational volumes for both VADs, the latter are still significant in size. Crucially, given that the axial design reduces the significant elongational stress volume, but increases that for shear stress, more experimental data is needed on elongational stress-induced damage, with which to inform the design of new VADs.

M3 - Meeting abstract

VL - 40

SP - 405

EP - 405

JO - The International Journal of Artificial Organs

T2 - The International Journal of Artificial Organs

JF - The International Journal of Artificial Organs

SN - 0391-3988

IS - 8

ER -