• No results found

Review: Development of Blood Flow through the Heart Valve Leaflet in Experimental Model

N/A
N/A
Protected

Academic year: 2020

Share "Review: Development of Blood Flow through the Heart Valve Leaflet in Experimental Model"

Copied!
5
0
0

Loading.... (view fulltext now)

Full text

(1)

AbstractHeart is a complex structure unit which pumps the blood throughout the body at a relevant high fluid velocity and pressure. The heart valve leaflet ensures the unidirectional flow of blood during a complete cardiac cycle. Many researches study on the structure and working principle of heart using both experimental and numerical principles and result a strong and value findings. Undeniable, experimental modeling of heart valve leaflet gives a better understanding toward heart function and thus enhances the development in biomechanics as well as artificial heart valve. This paper provided the detail review about the development in modeling of heart structure and heart valve leaflet experiments with respect to its method, material used and limitations.

Index Term— Blood Flow, Heart Valve Leaflet, Ventricle, Biomechanics

I. INTRODUCTION

The efficiency of a heart as a blood pumping unit measured not only on the force created by muscle during contraction, but also highly depends on the correct functioning of its heart valves. Most of the mammalian’s heart consists of four heart valves, every heart valves working periodically to ensure unidirectional flow of blood during cardiac cycle. A heart consists of four chambers, two of the valves located in between the upper and lower chambers (atrium and ventricle) on each side of heart: the tricuspid valve on the right; mitral valve on the left. Another two valves situated at the exit of ventricles: the pulmonary valve at the exit of right ventricle into pulmonary artery; aortic valve at the exit from the left

F. A. Mohd Azrul Hisham Mohd Adib from Sport & Human Engineering Group (SHEG), Faculty of Mechanical Engineering, Universiti Malaysia

Pahang, Pahang, Malaysia

azrul@ump.edu.my

S. B Kok Yin Hui from Faculty of Mechanical Engineering, Universiti Malaysia Pahang, Pahang, Malaysia

Cassandra_kyh@hotmail.com

T. C Nur Hazreen Mohd Hasni (MD), from Department of Surgery, Hospital Tengku Ampuan Afzan, Pahang, Malaysia.

F. D Mohamad Yazid Mohamad Yassin from Faculty of Mechanical Engineering, Universiti Malaysia Pahang, Pahang, Malaysia

ventricle into the aorta. From anatomically studies, heart valves can be categories into two types;

semilunar and atrio-ventricular regarding on their location in within the heart. Pulmonary valve (PV) and aortic valve (AV) are semilunar valves which prevent backflow of blood into ventricles. They form nearly a perfect circle and have three similarly sized leaflets and are called semilunar due to their half-moon shape. The major difference between AV and PV, besides the dimensions of leaflets, is that the AV has coronary ostioles behind two of the leaflets in the aortic wall, thus AV has comparative thicker fibrous structure than the PV [1]. Atrio-ventricular valves (also known as cuspid valves) refer to tricuspid valves and mitral valves which prevent the backflow of blood from ventricle to atrium during systole. They are more structurally complex as they are not formed of equal sized leaflets and do not have symmetrical geometries [1]. The number of leaflet can be identified from the naming: tricuspid valve made up of three leaflets; mitral valve (also known as bicuspid valves) made up of two leaflets. They are anchored to the inner wall of the ventricle by chordae tendineae. Chordae tendineae are attached to the papillary muscle to create tension for better holding of valve, which prevent the valve from inverting to the atrium during systole.

Fig. 1. Example experimental model from previous a) Ventricle model; b) Left ventricle model [4]

I. EXPERIMENTAL SETUP

In order to improve the understanding toward the heart valves function, the present study employs either experimental or numerical approaches or both. Experimental setup facilitates the understanding of a heart functions, thus numerous models have been developed by using different materials and methods to study about valve leaflet, blood flow and formation of

Review: Development of Blood Flow through the

Heart Valve Leaflet in Experimental Model

(2)

vortices in heart. The experiment methods and their limitation are summarized here.

A. Left Ventricular Fluid Dynamics Model

The paper of Combined Experimental and Numerical Analysis of the Flow Structure into the Left Ventricle prepared by F.Domenichini, G.Querzoli, A.Cenedese and G.Pedrizzetti had described an experiment setup to study about the fluid dynamics in left ventricle. The three-dimensional flow dynamic is analyzed in terms of its vertical structure.The experimental setup is sketched in Fig. 2. A model ventricle is made from transparent silicon rubber and placed inside a Plexiglas chamber. The high degree transparency ensures the best observation and fluid movement pictures capture. The chamber is filled with water and connected to a piston-cylinder device which driven by a computer-controlled linear motor. The movement of piston creates pressure different in chamber and thus causes the contraction and relaxation of ventricle. The base of the model ventricle has two circular orifices which model the mitral and aortic opening respectively. To avoid backflow, two one-way valves are inserted in each tube. The circuit is closed by two tubes that connect the orifices to a constant head reservoir. When the piston started pumping, the mitral and aortic valves open simultaneously to allow flow of fluid into the ventricle [2].

Fig. 2. Experiment modeling of Left Ventricle Fluid Dynamic Model [2]

B. The behavior of Leaflet with Difference Thickness Model

The paper of A Two-dimensional Fluid-Structure Interaction Model of the Aortic Valve, prepared by J. De Hart, G.w.m. Peters, P.J.G. Schreurs and F.P.T Baaijens, had conducted an experiments to study the behavior and deformation of leaflet during systole and diastole regarding to different leaflets’

thickness. This experiment controlled the thickness of leaflets to 0.16mm and 0.3mm respectively. A piston is used for pumping to create fluid movement and allow deformation of leaflets. Fig.3(a) and (b) shows the experiment setup used in this paper. The purpose of using diffuser, reservoirs and steady pump is to create laminar fluid flow instead of turbulence. The piston moves within a closed cylinder and is connected to a control card. It is then connected to a diffuser and measuring section. The measuring section consists of single valve leaflet which made of EPDM rubber (Ethylene-Propylene-Diene Monomer) [3].

(a).

(b).

Fig. 3. a) Experiment modeling of The Behavior of Leaflet with Different Thickness Model [3]; b) Single leaflet is used in measuring section [3]

The advantages of EPDM rubber is its low swell-grade, incompressible and isotropic properties. The deformation of leaflet is studied and captured during fluid flow. The measuring section is connected with reservoir 1 and reservoir 2. The water level of reservoir 2 must be higher than the piping vertical height to ensure the system is under full water supplied. The piping is further connected to a steady pump and finally back to the piston [3].

C. Blood Flow Study through Mitral Valve Model

(3)

anterior leaflet during inflow of blood into the left ventricle. The experiment is explained in detailed through sketching in Fig. 5. It was performed in a re-circulating water channel in which the constant water movement was driven using a wheel which connected to an electrical motor. The idealized model of the left ventricle was built using Styrofoam board which shaped using hot-wire cutter.

Noted that the Styrofoam board used must be non-porous to ensure no water passed through. The leaflets of Mitral valve were made using compliant plastic sheet and is placed slightly overlap at the tip of valve. A clearance of 1mm was left between the bottom of the water channel and the lower part of the leaflets to facilitate their opening. Flow straightness are placed before the leaflet in order to stabilize the fluid flow into laminar. The fluid flow was studied through the adding of silver color glitter dust into the water and captured using a 12mega pixels digital camera. Glitter dust is colored, non-soluble and suitable to be used as seedling. The top of the model is uncovered, thus the flow of glitter dust can be observed directly [4].

Fig. 4. Experimental Modeling of Blood Flow Study Through Mitral Valve Model [4]

D. Flow Study through Flexible Conduits Model

The paper of validation of a Fluid-Structure Interaction numerical model of predicting flow transients in Arteries prepared by V. Knyanta, A.Ivankovic and A. Karac, focuses its study on the interaction between the flowing blood and the deforming arterial wall to blood flow behavior. Although this experiment studies on arteries instead of heart valve, however, the setup of model can be a reference. Most of the experiment models setup using solid and rigid material as the arterial wall, this is different with actual human arterial structure which is

flexible and allow deformation, thus the accuracy of experiment is doubtful.

In this paper, the flow transients such as pressure, axial stress and precursor wave speeds, mock artery deformations and oscillating frequency and fluid velocity and Poisson coupling effects were used as the basis of this validation. The experimental setup is as shown in Fig. 4. The fluid used is not return-able. The inflow tank is used to provide a pressure head and the solenoid valves (V1 and V2) control the flow through the mock artery to create any pulsatile or unsteady flow condition. Since the deformations are small, the solid domain was modeled as linear elastic solid using polyurethane rubber tubing. The solid domain is surrounded by a fluid domain. Pressure transducers are connected before and after the fluid domain [5].

II. LIMITATION

The setup of various heart structure experiment models had contribute a lot to the understanding of human heart as well as to disease, injury and treatment. Human heart is a complex unit so thus raises the complexity in modeling the experiment model. Every heart valve experiment models has focuses on different study aspect, either blood flow pattern in heart, heart valve leaflet deformation or rigidity of heart valve. Most of the papers study about the fluid flow pattern through heart valve. This aspect reflects to us the detail structure of heart in effectively directing the blood, and same goes for the formation of vortices in heart. Without the vortices in the sinuses the valve still closes, but its closure is not as effective as when the vortices are present [1]. Besides, study on leaflet curvature and deformation during systole and diastole is important in develop artificial heart valve. Human heart valve is high rigidity which is able to repeat the opening and closing cycle rapidly under high pressure. However, every of the experiment models have the limitation of findings and setup. The inability in controlling system pressure and maintaining the continuity of fluid are one of the common issues. The comparison between experiments of review papers is shown in Table 1.

III. BLOOD COMPOSITION

(4)

up to 4.3 Ns/m². The density of the fluid is similar to water, which is around 1000kg/m³.

IV. FLUID FLOW

Fluid flow pattern can be classified into Laminar flow (Re ≤ 2000), Transitional flow (2000 < RE <4000) and Turbulent flow (Re ≥ 4000) based on the Reynard Number (Re). Blood flow in human arteries at high velocity and pressure, thus its Reynard Number is high and categories as Turbulent flow. However, turbulent flow is hard to be controlled and managed, thus it usually be ignored during modeling of experiment. From the review of papers, the fluid flow is controlled and assumed to be laminar flow. The purpose of installing a diffuser in the behavior of leaflet with different thickness model is to regulate the fluid from unsteady flow to steady and uniform flow by diverting the fluid through numerous small holes before entering the measuring section. For the same purpose, steady pump and flow straightener are applied in some heart valve experiment models. Laminar fluid flow gives a comparative constant effect the fluid flow. Thus, the fluid viscosity is important to be modified to be alike with the actual human blood viscosity in order to obtain a quality result. In the past research study, the measures of blood viscosity in the younger group (aged 18-60) was significantly lower than in the senior group (aged 61 and above). Besides, some of the experiment models have installed one-way-valve in directing the fluid flow in one single direction and prevent backflow. In actual case, a small percentage of backflow is present during blood flow through heart valve. However, the amount of blood undergoes backflow is very less (exclude heart disease patients) and thus it is reasonable and usually being ignored in modeling the experiment in order to obtain a better result of study.

Fig. 5. Effect of age and gender on blood viscosity [8]

V.MEASURING DEVICE

Pressure transducer is a common pressure measuring device used in the experiment models with closed system. Besides, to

study the leaflet curvature and deformation, a high speed camera will be the best helper in recording the leaflet changes with respect to fluid flow. A higher resolution of camera is preferred for better image captured. On the other hand, a Laser Doppler Anemometry (LDA) is used to measure the fluid velocities two dimensionally. The method is based on the dual beam backward-scattered principle and is suitable to detect high-speed flow velocities. However, to apply the LDA, PMMA particles (polymethyl-metacrylate) of 10µm diameter were added to the solution as a seeding scattering back the laser light generated by the LDA system [3]. In the paper of Blood flow study through mitral valve model, silver color glitter dust which widely used in nail art decoration is

added to the fluid to study the fluid flow line and pattern. TABLE I

LIMITATION OF EXPERIMENTAL MODELING

Coverage of Experiment setup

O – the issue is covered in the experiment model X – The issue is not covered in the experiment model

VI. CONCLUSION

As a conclusion, various heart valve experiment models were setup to study about the human heart structure and function. Although various limitation exist in modeling the experiment which act as an obstacles for further analyze and detail study of heart structure, however, the matching between the result of experimental and numerical has proved the reliability of research’s result.

ACKNOWLEDGEMENTS

The support of the Universiti Malaysia Pahang, under grant RDU110331 and under SHEG group is gratefully

Paper Review St u d y o n fl u id fl o w p at tern St u d y o n l eafl et d efo rmat io n St u d y o n t h e v o rt ices fo rmat io n Ability in contr olling sy st em p res su re Ability in m ainta ining co n ti n u it y fl u id fl o w Left ventricular fluid dynamics

model O X O X O

The behavior of leaflet with

different

thickness model X O X O O

Blood flow study through

mitral valve

model O O O X O

Flow study through flexible

(5)

acknowledged. The authors of this paper also would like to express their gratitude to Hospital Tengku Ampuan Afzan (HTAA) for supporting these research activities.

REFERENCES

[1] Micheal S. Sacks, W. David Merryman, David E. Schmidt, Review On

the Biomechanics of Heart Valve Function, Journal of Biomechanics 42: 1804-1821, (2009)

[2] F. Domenichini, G. Querzoli, A. Cenedese, G. Pedrizzetti, Combined

Experimental and Numarical Analysis of the Flow Structure into the Left Ventricle, Journal of Biomechanics 40: 1988-1994, (2007)

[3] J. De Hart, G.W.M. Peters, P.J.G. Schreurs, F.P.T. Baaijens, A

Two-dimensional Fluid-structure Interaction Model of the Aortic Valve, Journal of Biomechanics 33: 1079-1088, (2000)

[4] Mushtak AL-ATABI, Daniel M. Espino, David W.L. Hukins, Computer

and Experimental Modelling of Blood Flow through the Mitral Valve of the Heart, Journal of Biomechanical Science and Engineering, Vol. 5, No. 1, (2010)

[5] V. Kanyanta, A. Ivankovic, A. Karac, Validation of a Fluid-structure

Interaction Numerical Model for Predicting Flow Transients in Arteries, Journal of Biomechanics 42: 1705-1712, (2009)

[6] Woodward, M., Rumley, A., Tunstall-Pedoe, H., Lowe, G.D.O, Does

Sticky Blood Predict a Sticky End? Association of blood viscosity, haemotocrit and fibrinogen with mortality in the West of Scotland. Br. J. Haematol. 122: 645-650, (2003)

[7] Reinhart, W.H, Molecular Biology and Self-Regulatory Mechanisms of

Blood Viscosity: A Review, Biorheology 38 (2-3): 203-212, (2001)

[8] J.C.F. Galduroz, H.K. Antunes, R.F. Santos, Gender- and Age-related

Variations in Blood Viscosity in Normal Volunteers: A Study of the Effects of Extract of Allium Sativum and Ginkgo Biloba, Phytomdedicine 12: 447-451, (2007)

[9] B. Skallerud, V. Prot, I.S. Nordrum, Modeling Active Muscle

Contraction in Mitral Valve Leaflets during Systole: A First Approach, Biomech Model Mechanobiol 10: 11-26, (2011)

[10] Sihe Wang, Anders H. Boss, Kenneth R. Kensey, Robert S. Rosenson,

Figure

Fig. 1. Example experimental model from previous a) Ventricle model; b) Left ventricle model [4]
Fig. 2. Experiment modeling of Left Ventricle Fluid  Dynamic Model [2]
Fig. 4. Experimental Modeling of Blood Flow Study Through Mitral Valve  Table 1. Model [4]

References

Related documents

First, foreign firms in emerging countries face greater environmental risks (Puck et al., 2013) owing to the volatility and fragility of the institutions in

The existing differences of productive yields between organic and conventional vineyard productions of this cultivation are clearly compensated because of the

From a tax perspective, there is a strong treaty network, a dividend exemption, an exemption from capital gains on disposal of shares, and no withholding tax on dividends, although

the PCehr is the term used within the national health and hospitals reform Commission’s (nhhrC) report in 2009 44 and proposed in the Australian Federal budget 2010-11; announcing

Key Words : Business Women, Decision making, Entrepreneur, Enterprise, Equality, familial, Economics, Skill, training, vocational education, entrepreneurship

Relative IDWG &gt; 3.5 % body weight was independently associated with all outcomes studied: point estimates ranged from 1.18 (myocardial infarction) to 1.26 (CV mortality) and

To assess the risk of resistance breakdown, the resistance of four barley cultivars (‘AAC Synergy’, ‘CDC Meredith’, ‘Cerveza’ and ‘Major’), previously identified as

There is an old Wall Street adage, which says, “The market is always right.” And while most so-called words of wisdom regarding the stock market are useless at best, this is one