(601ap) Relationship Between Turbulent Quantities and Hemolysis

Mesude Ozturk^b, Edgar A. O’Rear^a,b and Dimitrios V. Papavassiliou^b

^aUniversity of Oklahoma Bioengineering Center, Norman, OK, USA and ^bDepartment of Chemical, Biological and Materials Engineering, University of Oklahoma, Norman, OK, USA

Examining the turbulence effects on red blood cell (RBC) trauma is of major importance when designing prosthetic heart devices that are often used as an efficient treatment to heart failure.  Ventricular assist devices (VAD) are a commonly used prosthetic heart devices and they introduce an efficient therapy to the patients who are in advanced level of sickness to wait for a heart donor or who are not suitable for transplantation [1]. Ventricular assist devices are being used for therapy of patients for their heart transplantation initially, but now they are used as lifetime support [1]. Development and optimization of better designs of VAD devices will help patients to recover fast and return their normal life.  Optimization of VAD devices to avoid hemolysis, therefore, depends on understanding and predicting the effect of turbulent stresses on RBCs. In this work, computational fluid dynamics (CFD) was used to calculate flow characteristics and to relate them to cell damage. The CFD simulations are designed to simulate prior, well documented experiments. In order to understand better the structure and effects of turbulence on the cells, we compared the hemolysis observed for 5 Couette viscometer experiments [2] and 4 capillary tube experiments [3] to the characteristics of turbulence in the flow. There is no clear consensus on which turbulence features exactly are causing blood damage, and prior work has focused on wall stresses, and on Reynolds stresses, and on turbulence length scales associated with the dissipation of the turbulent kinetic energy, i.e., the Kolmogorov length scales (KLS) of the flow. The argument for the case of a stress-related hemolysis mechanism is that there is a threshold stress beyond which the RBC membranes undergo trauma, while the argument for the KLS is that the RBCs need to be in areas of the flow where the turbulence eddies are small enough to transfer energy to the RBCs and cause damage to them. These dissipation scales are very difficult to obtain experimentally, since measuring the dissipation of turbulent kinetic energy requires accurate measurements of the fluctuating velocity gradient in all three space directions. With CFD, we calculated all of the aforementioned quantities using a finite-volume based scheme and the k-epsilon model for turbulence. We examined carefully the relation between calculated Kolmogorov length scales and Reynolds stresses with the observed levels of hemolysis in each experiment. Commonly used hemolysis models that are based on time of exposure and stress, e.g., the Giersiepen et al. [4] and the Heuser et al. [5] models, were also evaluated against the calculated results and the experimental findings. Finally, we have searched for relationships with hemolysis predictions and different characteristics of turbulent flow conditions, such as the total surface area of turbulent eddies with different KLS. It appears that this is the parameter that is more strongly related with the appearance of hemolysis. Implications for the design of medical devices will be discussed in the presentation.

References

1.         Givertz, M.M., Ventricular Assist Devices Important Information for Patients and Families. American heart asscoiation, 2011.

2.         Sutera, S.P. and M.H. Mehrjardi, Deformation and Fragmentation of Human Red Blood Cells in Turbulent Shear Flow. Biophysical journal, 1975. 15.

3.         Kameneva, M.V., et al., Effects of Turbulent Stresses upon Mechanical Hemolysis: Experimental and Computational Analysis. ASAIO Journal, 2004. 50: p. 418-423.

4.         Giersiepen, M., et al., Estimation of shear stress-related blood damage in heart valve prostheses-in vitro comparison of 25 aortic valves. The International Journal of Artificial Organs, 1990. 13(5): p. 300-306.

5.         Heuser, G. and R. Opitz, A Couette Viscometer for Short Time Shearing of Blood. Biorheology, 1980. 17: p. 17-24.