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Blood Pumps Project 48641 – Fluid Mechanic

University of Technology, Sydney Autumn 2017

Blood Pumps Project

48641 – Fluid Mechanic

Table of Contents Abstract ...................................................................................................................... 3 Background to the development of Blood Pumps....................................................... 4 Development of artificial pumping of blood..................................................... 6 Human blood as fluid .................................................................................................. 7 The comparison of blood pumps versus water pumps................................................ 9 Components and operation principle.............................................................. 9 Material and dimensions............................................................................... 11 Life expectancy and maintenance................................................................ 12 Blood pump issues especially relating to fluid mechanics......................................... 13 Flow rate and pressures............................................................................... 13 Equations related to flow rate....................................................................... 13 Resistance to flow..............................................................................13 Flow Rate..........................................................................................13 Rotational speed................................................................................14 Heart Valves Fluid mechanics...................................................................... 15 Issue of blood damage and blood clot...................................................................... 17 Blood damage .............................................................................................. 17 Danger of Blood clot..................................................................................... 17 Thrombosis .................................................................................................. 17 Haemolysis .................................................................................................. 18 How fluid mechanics applies to solve the issues by using blood pumps...................20 Comparison of key aspects pertaining to blood pumps of different designs and.......22 Roller Pumps ................................................................................................ 22 Centrifugal Pumps........................................................................................ 23 Axial Pumps ................................................................................................. 25 Nonocculsive Roller..................................................................................... 25 Important outstanding issues relating to blood pumps and directions for their..........30 Blood Damage ............................................................................................. 30 Foreign Surface Contact.............................................................................. 30 Cavitation ..................................................................................................... 30 Damage from Pumps................................................................................... 31 Conclusion ................................................................................................................ 32 References ............................................................................................................... 33 Page 2

Blood Pumps Project

48641 – Fluid Mechanic

Abstract The fundamental principles of fluid mechanics have a principal role in the development, feasibility and future progress of blood pump technologies. This project aims to highlight the importance of fluid mechanics in the technology of blood pumps as well as a background to the development of its medical instrument will be mentioned and discussed in detail. The Key aspects of projects is the comparison between blood pumps and water pumps and the different types of blood pumps utilizing currently in today’s technology will also be studied in detail.

Blood Pumps Project

48641 – Fluid Mechanic

Background to the development of Blood Pumps The tissues of the human body require an enough of nutrition to survive. The heart is one of the most important parts of the internal organ in human because it pumps blood to the other organs and tissues by the circulatory system, supplying oxygen and removing carbon dioxide and so on. If the heart stop supplying blood throughout the body, it will stop functioning. Deoxygenated blood enters into the right atrium via the superior vena cava and the inferior vena cava. Then, it passes into the right ventricle and is pumped into the lung via the pulmonary artery which direct the blood to the lungs to remove carbon dioxide and absorb oxygen. The oxygenated blood coming out from the lungs is received by the left atrium. After that, the left atrium pumps that blood which distributes oxygen and nutrients into the body via the aorta. The blood is circulating as a loop across the body by delivering oxygen and collecting metabolic wastes, and returns back to the heart (Lewis T, 2016). Heart pumps all day to circulate blood around the body. A red blood cell in the circulation passes through the heart every 45 seconds on average. For an adult, the heart beats about 60 to 80 times per minute. The heart is compose of muscle; it essentials a supply of oxygen and nutrients to pump effectively, too. Two sets of arteries: left main coronary artery and right coronary artery work as blood carriers to feed oxygenated blood to the heart muscles (Phillip L,nd).

Figure 1: Anatomy of the human heart .

The heart and the blood vessels are the essential components of a cardiovascular system. Occurring disorders in the function of any part of the cardiovascular system are known as cardiovascular diseases. When the heart is not pumping enough blood around the body, the heart is severely failing. Heart failure is one of the common types of cardiovascular diseases and it happens when the heart is unable to provide sufficient pump action to maintain blood flow to meet the needs of the body (MedicineNet, 2014). According to the UW Machine 2017, about 287,000 people die every year. Thus, artificial blood pumps are invented as the mechanical device that enables the failing heart to maintain a sufficient blood circulation through the body.

They operates with two devices: ventricular devices (VADs) or the total artificial heart (TAH). The VAD may be connected to atrium, ventricle, the aorta and the artery to the heart according to the side of the heart needs. Total artificial heart is put into the body when the heart has been removed. It means it is a mechanical substitute a mechanical substitute for the entire heart.

Development of artificial pumping of blood The extracorporeal heart-lung circuit is made up of a gas exchange device, a blood pump, heat exchanger and so on. A blood pump plays as a vital role in the circuit because it pumps the oxygenated blood to the whole body. In 1928, two main pumps are introduced by Dale and Schuster: diaphragm pump and the roller pump. After that a multiple finger pump was so popular around 1954 which was designed by biomedical

engineers and

cardiac

surgeons

at

the

Minnesota

University.

Unfortunately, using the multiple finger pump at high speeds caused hemolysis. In 1855, Porter and Bradley patented the roller pump which used as a scavenger for the cleaning of privies or as a stomach pump. Later, the pump uses a roller that progresses along a blood containing resilient tube propelling the blood column in front of the roller and out of the pump. In 1891, Truax named the pump as surgical pump. In 1934, DeBakery and Schmidt made a modification of Porter-Bradley infusion pump for solving the creep age problem. It had a flange to the outer circumstance of the tubing. But in reality, it could only use for cardiopulmonary bypass. In 1959, Melrose advanced the design. The roller was put in place by a grooved backplate while the radius of the roller and groove is fixed (Texas Heart Institute Journal 1987). During operation, the tube guides protected the horizontal motion. Nowadays, there are several types which have been used in the extracorporeal circuit.

Blood Pumps Project

48641 – Fluid Mechanic

Human blood as fluid In human body, about 8% of the weight is blood. Females have around 4 to 5 litre. Males have around 5 to 6 litre. The blood’s temperature is 38 degrees Celsius. Moreover, pH level of the blood is less than 7(7.35-7.45). Blood is the essential fluid in the body. It transports oxygen and nutrients to the cells. O'Neil, 2013 states that blood is composed of more than 4000 different kinds of components. Blood is made up of two main components: plasma and formed elements. Former is a clear extracellular fluid and the latter is composed of the blood cells: red cells, white cells and platelets.

Figure 2: The components of blood. .

The density of blood plasma is around 1025 kg/m and the density of the blood cells is approximately 1125kg/m. Plasma is yellow tinted water which carriers the red cells, white cells and platelets. Actually, 55 percent of the volume of blood is made up of plasma (O’Neil D, 2013). Blood plasma is a mixture of proteins, enzymes and so on.

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If part of the body gets the vascular injury, plasma proteins protect to be less in the loss

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Blood Pumps Project

48641 – Fluid Mechanic

of blood. The distribution of water between blood and tissue fluid is known as a colloid osmotic pressure. Comparing with fluid, blood is about 5 times as viscous as water. The viscosity is really vital in the function of blood because it makes blood to flow with too much resistance; it can strain the heart. When people are become older, blood viscosity and plasma viscosity is also increasing. A state of hyperviscosity occur sluggish blood flow. As described above, human blood is kind of fluid. And also, it is more viscous than water thus there is viscosity. By knowing the general properties of the blood, engineers can be able to design the blood pump which is useful in the human body to minimize the damage to the blood.

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Blood Pumps Project

48641 – Fluid Mechanic

The comparison of blood pumps versus water pumps The similarity between water pump and blood pump is both of them are the centrifugal pump. Water pump is a mechanism which helps to transport the water in different locations. Moreover, blood pump is a medical instrument which can replace the task of heart and pumping blood throughout the body. Moreover, in term of density between blood and water is also quite similar which the density of blood is 1060 kg/m3 and 1000 kg/m3 is the density of water. Furthermore, for comparison more specifically between blood pump and water pump, it should be separated into several parts: 

Components and operation principle



Material and dimensions



Life expectancy and maintenance

Components and operation principle Normally, a water pump includes some parts are Housing/casing, impeller, motor, shaft, volute, bearing assembly, hub and seal (Engineering 360, 2017). Moreover, the principle component of water pump can easily see that like a black box. A certain velocity and pressure of water enter to the pump and leave it with increased energy. This pump use energy from external source and usually is electricity. The moving of fluid in the pump by confining it indefinite volumes and increasing velocity and pressure (Naveenagrawal, 2009). Moreover, the components of blood pump is quite simple which includes outlet, inlet, impeller and power supply. As above, the blood pump is a medical instrument which can replace the task of heart and it connect to two valves of the heart to pump blood throughout the body.

Figure 3: Water pump components .

Figure 4: Blood Pump components .

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Material and dimensions The material between water pump and blood pump also are different which water pump has many parts and normally using in the environment which is affected by many external conditions. There are some components of water pump and material for those. The housing is the outer shell of the pump and made from cast iron or aluminium. Besides that, the bearing assembly is made from steel and rubber and support for the rotation of impeller. Impeller is a set of vanes coupled to a shaft and connect to rotating disk, it can impart energy to induce flow and the material is steel, cast iron and plastic. Moreover, steel or cast iron also can be used for the hub and it attach to the impeller’s source of power. Finally, the material for seal is softer which are silicon or carbide for protecting the bearing assembly (Engineering 360, 2017). In addition, the dimension of water pump is depend on many conditions, which are: 

The environment for using



The volume of fluid which need to be imparted



The distance between the source and destination

However, blood pump is only use for human therefore it expect to as small as possible because it will decrease the weight of pump in the body and does not create many obstacles.

Figure 5: Blood pump sets up inside the body .

Life expectancy and maintenance Water pump is cooling or antifreeze for the engine in the car. Besides that, the life expectancy of it this pump is quite long. Moreover, water pump is easier than the other machines for maintenance hence timing belt need to be replaced after serviced for a long time (Neiger, 2010). On the other hand, the life expectancy and maintenance of the blood pump required the helping from the specialist surgeon because with a smallest mistake can leads to worst result for patient.

Blood pump issues especially relating to fluid mechanics In fluid mechanics, fluid objects and its characteristics are mainly covered. Therefore, by further emphasizing the effect of fluid, there is a correlation between blood and fluid mechanics. There are factors that must be considered relating with blood in this project and those are Flow rate, Pressure, Size and material type, Rotational Speed, and Power Supply.

Flow rate and pressures The concept of flow rates and pressures are also main fundamental concepts of blood. There are few main theories and formulas to determine or calculate the flowrate in turbulent or laminar. For a laminar flow, velocity of effective is half the maximum velocity. At a certain velocity, the flow will be turbulent which increases the pressure and resistance and thus, increases the volume flow rate. Typically in medical terms the pressure inside the heart is often referred to as “Blood Pressure”

Equations related to flow rate Resistance to flow:

∆P F= R

Where F = Blood Flow (m/s); P = Pressure, R = Resistance And Resistance can be calculated by using the formula 8vL R = r4rr Where v = Fluid Viscosity; L = Length of tube (m); r = radius of tube (m)

Flow Rate:

Q = VA

Where Q = Flow Rate; V = Velocity; A = Area V (critical) = μ*Re/ρ*D where R= Reynold’s number and it is about 2000 for blood flow.

Blood Pumps Project

48641 – Fluid Mechanic

Rotational speed Rotational speed is also an important factor for blood. It is based on a low specific speed centrifugal pump which is use in a semi open impeller with magnets. There are few relevance and derivate equations related to rotational speed. The following are a few equations for calculating Power for this rotary pump: Torque(T) from the rotary pump on the surrounding area d T=F 2 Where T = Torque; d = diameter; F = Force Calculation of F F = T ∗ Area Calculation of r µrw T=

h

Where µ = Fluid Viscosity; r = radius; w = rpm; h = length

Torque produced from bottom plate to rotary spin 2rrµwr4 T=

4h

Where T = Torque; µ = Fluid Viscosity; w = rpm; r = diameter; h = height And the Power is calculated by P = Tw Where P = Power; T = Torque; w = rpm (rotation per minute)

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Blood Pumps Project

48641 – Fluid Mechanic

Heart Valves Fluid mechanics Artificial heart valves have been used for over 50 years to replace heart valves that are diseased. Currently, there are many ways to solve using fluid mechanics for the major artificial heart valve types and highlight how the engineering approach has covered the awareness of this issue. According to HHS Public Centre (2009), there are two main types of artificial heart valves and they are mechanical and bioprosthetic heart valves, and they are very complicated. There are six types of prosthetic heart valves while mechanical heart valves have issues regarding to haemolysis, platelet activation and thromboembolic events arising from clot formation and their subsequent detachment. These complicated properties of heart valves are well related to one of the main property of fluid mechanics and that is the blood flow patterns in the vicinity of heart valves. Abnormal flow patterns can cause tearing of the blood elements, that leads to haemolysis as mentioned above. There are various types of heart valves realted to fluid mechanics depending on its behaviour of flow rates. Those are ball and cage valves, tilting-disc valve, bileaflet valve, trileaflet valve. For valve performances, clinicans have improced two parameters to test the level of stenosis and those are effective orifice area (EOA) and the volume. Effective orifice area is a measure of the valve that is mainly effected during forward flow phase whereas the volume is a measure of the back flow. The EOA has a relation basically with conservation of energy and have two main propeties determining which is flow and pressure drop. The formula calculated

as

for

EOA

can

be

below. EOA (cm2) = Qrms * 51.6 * ∆p

Where Qrms is the root mean square systolic/diastolic flow rate (cm 3/s) and ∆ p is the mean systolic/diastolic pressure drop (mmHg). Further important properties such as turbulence stress levels resulted by blood cells and turbulent flow have been utilized to test the potential of the blood valves. The values of turbulent stress level between 10 – 100 Pa are known to get on platelet activation whereas the threshold for hemolysis is higher than 800 Pa.

Figure 6: The figure shows the bileaflet mechanical heart valve in the aortic position during the leakage flow. It also includes the red blood cless getting damaged due to leakage gaps.

Figure 7: The figure above shows the two streams which are forward flow phase (left) and the leakage flow phase (right).

Issue of blood damage and blood clot Naturally, the human body already has potential vulnerabilities. However, with the supporting from medical equipment that leads to more dangers and the blood pumps are not exception. It caused to two issues are blood damage and blood clot.

Blood damage The elongation of the red blood cells by blood pumps will leads to spill out of haemoglobin to the plasma and that is blood damage. It can occur by thrombosis or haemolysis (CATS, 2017).

Danger of Blood clot Clotting is a natural factor in the blood which ensure to stop the bleed in the case the body has been cut. However, in some conditions such as hypertension or atherosclerosis which can lead to the blood clot. Moreover, a heart attack ...