Experimental measurement and numerical modelling of dye washout for investigation of blood residence time in ventricular assist devices

Molteni, Alessandra; Masri, Zubair Ph; Low, Kenny; Yousef, Haitham N.S.; Sienz, Johann; Fraser, Katharine

doi:10.1177/0391398817752877

Cited by 16 publications

(13 citation statements)

References 51 publications

(68 reference statements)

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“…It therefore appears that washout is governed largely by the device geometry and pump flow rate. The time required for 95% washout was comparable to that found in the HVAD, which features a secondary flow path similar to the HM3 . Notably, the implemented scalar only characterizes washout of a fully soluble quantity, neglecting effects like mechanical interaction with the wall or biological interaction between blood components.…”

Section: Discussionmentioning

confidence: 83%

Fluid Dynamics in the HeartMate 3: Influence of the Artificial Pulse Feature and Residual Cardiac Pulsation

et al. 2018

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Ventricular assist devices (VADs), among which the HeartMate 3 (HM3) is the latest clinically approved representative, are often the therapy of choice for patients with end-stage heart failure. Despite advances in the prevention of pump thrombosis, rates of stroke and bleeding remain high. These complications are attributed to the flow field within the VAD, among other factors. One of the HM3's characteristic features is an artificial pulse that changes the rotor speed periodically by 4000 rpm, which is meant to reduce zones of recirculation and stasis. In this study, we investigated the effect of this speed modulation on the flow fields and stresses using high-resolution computational fluid dynamics. To this end, we compared Eulerian and Lagrangian features of the flow fields during constant pump operation, during operation with the artificial pulse feature, and with the effect of the residual native cardiac cycle. We observed good washout in all investigated situations, which may explain the low incidence rates of pump thrombosis. The artificial pulse had no additional benefit on scalar washout performance, but it induced rapid variations in the flow velocity and its gradients. This may be relevant for the removal of deposits in the pump. Overall, we found that viscous stresses in the HM3 were lower than in other current VADs. However, the artificial pulse substantially increased turbulence, and thereby also total stresses, which may contribute to clinically observed issues related to hemocompatibility.

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Section: Discussionmentioning

confidence: 83%

Fluid Dynamics in the HeartMate 3: Influence of the Artificial Pulse Feature and Residual Cardiac Pulsation

et al. 2018

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“…A comparison between experiments and CFD was performed only by analyzing the pressure heads. Although the validation of pressure heads is not as valuable as a full validation of the velocity or turbulent kinetic energy field, it is an appropriate and commonly used validation method 16 , 18 , 23 , 44 to analyze the suitability of a numerical model. The validation of the H–Q curve holds as a first step of flow validation, since an incorrectly computed flow field will also lead to incorrectly computed pressure heads.…”

Section: Resultsmentioning

confidence: 99%

Influence of turbulent shear stresses on the numerical blood damage prediction in a ventricular assist device

2019

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The blood damage prediction in rotary blood pumps is an important procedure to evaluate the hemocompatibility of such systems. Blood damage is caused by shear stresses to the blood cells and their exposure times. The total impact of an equivalent shear stress can only be taken into account when turbulent stresses are included in the blood damage prediction. The aim of this article was to analyze the influence of the turbulent stresses on the damage prediction in a rotary blood pump’s flow. Therefore, the flow in a research blood pump was computed using large eddy simulations. A highly turbulence-resolving setup was used in order to directly resolve most of the computed stresses. The simulations were performed at the design point and an operation point with lower flow rate. Blood damage was predicted using three damage models (volumetric analysis of exceeded stress thresholds, hemolysis transport equation, and hemolysis approximation via volume integral) and two shear stress definitions (with and without turbulent stresses). For both simulations, turbulent stresses are the dominant stresses away from the walls. Here, they act in a range between 9 and 50 Pa. Nonetheless, the mean stresses in the proximity of the walls reach levels, which are one order of magnitude higher. Due to this, the turbulent stresses have a small impact on the results of the hemolysis prediction. Yet, turbulent stresses should be included in the damage prediction, since they belong to the total equivalent stress definition and could impact the damage on proteins or platelets.

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“…The residence time in the very high normal stress regions (>1000 Pa) in these works can be estimated as 0.003 17 and 0.06 ms, 19 in contrast with average times of 0.87-2.1 ms in the cell deformation regions found here, and with average total times of 144 and 84 ms in the HVAD and HMII respectively. 42 There are no experimental studies which measured thresholds for haemolysis with normal stress exposure times around 1 ms.…”

Section: Discussionmentioning

confidence: 99%

Normal fluid stresses are prevalent in rotary ventricular assist devices: A computational fluid dynamics analysis

et al. 2018

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Despite the evolution of ventricular assist devices, ventricular assist device patients still suffer from complications due to the damage to blood by fluid dynamic stress. Since rotary ventricular assist devices are assumed to exert mainly shear stress, studies of blood damage are based on shear flow experiments. However, measurements and simulations of cell and protein deformation show normal and shear stresses deform, and potentially damage, cells and proteins differently. The aim was to use computational fluid dynamics to assess the prevalence of normal stress, in comparison with shear stress, in rotary ventricular assist devices. Our calculations showed normal stresses do occur in rotary ventricular assist devices: the fluid volumes experiencing normal stress above 10 Pa were 0.011 mL (0.092%) and 0.027 mL (0.39%) for the HeartWare HVAD and HeartMate II (HMII), and normal stresses over 100 Pa were present. However, the shear stress volumes were up to two orders of magnitude larger than the normal stress volumes. Considering thresholds for red blood cell and von Willebrand factor deformation by normal and shear stresses, the fluid volumes causing deformation by normal stress were between 2.5 and 5 times the size of those causing deformation by shear stress. The exposure times to the individual normal stress deformation regions were around 1 ms. The results clearly show, for the first time, that while blood within rotary ventricular assist devices experiences more shear stress at much higher magnitudes as compared with normal stress, there is sufficient normal stress exposure present to cause deformation of, and potentially damage to, the blood components. This study is the first to quantify the fluid stress components in real blood contacting devices.

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Experimental measurement and numerical modelling of dye washout for investigation of blood residence time in ventricular assist devices

Cited by 16 publications

References 51 publications

Fluid Dynamics in the HeartMate 3: Influence of the Artificial Pulse Feature and Residual Cardiac Pulsation

Fluid Dynamics in the HeartMate 3: Influence of the Artificial Pulse Feature and Residual Cardiac Pulsation

Influence of turbulent shear stresses on the numerical blood damage prediction in a ventricular assist device

Normal fluid stresses are prevalent in rotary ventricular assist devices: A computational fluid dynamics analysis

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