The use of computational fluid dynamics in the development of ventricular assist devices

Abstract

Progress in the field of prosthetic cardiovascular devices has significantly contributed to the rapid advancements in cardiac therapy during the last four decades. The concept of mechanical circulatory assistance was established with the first successful clinical use of heart-lung machines for cardiopulmonary bypass. Since then a variety of devices have been developed to replace or assist diseased components of the cardiovascular system. Ventricular assist devices (VADs) are basically mechanical pumps designed to augment or replace the function of one or more chambers of the failing heart.Computational Fluid Dynamics (CFD) is an attractive tool in the development process of VADs, allowing numerous different designs to be characterized for their functional performance virtually, for a wide range of operating conditions, without the physical device being fabricated. However, VADs operate in a flow regime which is traditionally difficult to simulate; the transitional region at the boundary of laminar and turbulent flow. Hence different methods have been used and the best approach is debatable. In addition to these fundamental fluid dynamic issues, blood consists of biological cells. Device-induced biological complications are a serious consequence of VAD use. The complications include blood damage (haemolysis, blood cell activation), thrombosis and emboli. Patients are required to take anticoagulation medication constantly which may cause bleeding. Despite many efforts blood damage models have still not been implemented satisfactorily into numerical analysis of VADs, which severely undermines the full potential of CFD. This paper reviews the current state of the art CFD for analysis of blood pumps, including a practical critical review of the studies to date, which should help device designers choose the most appropriate methods; a summary of blood damage models and the difficulties in implementing them into CFD; and current gaps in knowledge and areas for future work.

Hemolysis Prediction by using a Power-Law Mathematical Model in an Aortic Arterial Section

“…These models allow the identification of blood trauma regions in the design and evaluation of medical devices. Actually, CFD has been widely applied as tool in the blood damage prediction for implantable devices [6] [8] [9]. To finish: "These methods to quantify the blood trauma induced by artificial organs or implantable devices would reduce efforts and costs of design and development, and could be helpful in the assessments of clinical working conditions to minimize the impact of medical devices on blood cells" [3].…”

“…These models should describe the sustained blood damage by RBCs when they are under unsteady stress conditions, taking into account the load history. Computational fluid dynamics (CFD) is an important design tool to analyze the blood damage; because allows to determinate velocity profiles, shear stress, recirculation and stagnation zones of the blood flow [9].…”

Reynolds Stresses and Hemolysis in Turbulent Flow Examined by Threshold Analysis

“…Artificial hearts and ventricular assist devices create non-physiological blood flow conditions [1], such as turbulence [2,3], causing red blood cell (RBC) damage, an important consideration in the design of prosthetic heart devices. Turbulent flow means that irregular, random, chaotic, and multiscale flow conditions prevail with a wide range of time and length scales that cause harmful effects in blood, because of significant fluctuations in shear stresses and pressure.…”

“…Constants α, β, and C were determined from regression analysis applied to experimental data for shear stresses less than 255 Pa and exposure times less than 700 ms. Heuser and Opitz [10] obtained their set of coefficients using laminar flow in a Couette viscometer to determine hemolysis of porcine blood for exposure times less than 700 ms and shear stresses less than 255 Pa. Zhang et al [11] examined hemolysis of ovine blood for exposure times of less than 1500 ms and shear stresses between 50-320 Pa and obtained power law constants by fitting the hemolysis results to Equation (1). It has, however, been argued that since power law models were obtained by using viscometer experiments with steady, uniform laminar flow shear stress, the models often fail when capturing the general flow features of typical medical devices [26] which usually impose multiple, shorter term exposures.…”

Modelagem matemática da fluidodinâmica não-newtoniana e bifásica simplificada da hemólise induzida mecanicamente em sistemas de bombeamento centrífugo de sangue

“…Falando mais especificamente na aplicação de técnicas de dinâmica dos fluidos computacional ao universo das bombas de sangue, nota-se sua ampla utilização a partir do início dos anos 90, com estudos iniciais focados na avaliação de desempenho fluidodinâmico 6 , (Sukuma et al, 1996), (Frank et al, 2002), (Behbahani et al, 2009), , , (Fraser et al, 2011), . Há também alguns estudos sobre a distribuição da tensão de cisalhamento em diferentes regiões das bombas, particularmente para a análise de projetos ou implementação de melhorias (Untaroiu et al, 2005), (Kido et al, 2006), (Legendre et al, 2008a), , .…”