Blood Pump Issues Related to Fluid Mechanics

NB: We do not resell your papers. Upon ordering, we do an original paper exclusively for you.

NB: All your data is kept safe from the public.

Table of Contents

Torque
Rotational speed
Flow rate
Turbulence
Reliability of blood pump
References

Blood pumps are temporary devices that offer aid to patients suffering from severe heart diseases. They are classified into two main categories. These categories are displacement and rotary pumps (Cartier 2005, p. 45). The equipment are expected to operate in the same way the natural hearts operate. Owing to this, their designs are very difficult to achieve. The apparatus must function over a broad range of flow rates, pressure heads, rotational speed, power supply, torque, and turbulence. When coming up with the apparatus, care should be taken to achieve the right design that will accommodate both the children and adult patients. In the recent past, advancements in computational fluid dynamics have enhanced the design process of these devices (Parker 2006, p. 32). This paper highlights the issues related to fluid mechanics.

Torque

One of the main issues associated with the use of blood pumps is that it leads to body trauma. The trauma occurs due to the tissues restraining the pump owing to the differential reaction forces and the canals connecting the pump entry and exit to the human heart. The output torque is determined by the output pressure (p) of the pump and the radius to the center of pressure (rcp) of the throat cross-sectional area (A). The resultant torque for a BVAD will depend on the direction of the LVAD output with respect to the RVAD outlet and is given by the below equation (Peto 2007, p. 156). In the equation, the pressure of RVAD is 0.2 times of LVAD.

T_{BVAD. tot} = ((PA*r_cp) _throat) _LVAD+ (( 0.2PA *r_cp) _throat) _RVAD

Rotational speed

To calculate the rotational speed of these devices, flow visualization is undertaken to find out the flow patterns. At the impeller, very high rotational speeds exist. Owing to this, it is very hard to see the flow near the vanes. It is estimated that the rotational speed of these devices is some hundred revolutions per minute. These revolutions can be observed with the help of a high-speed camera.

Flow rate

Naturally, the heart generates enough pressure to overcome gravity and the force of friction between flowing blood and the vessel wall. In an artificial blood pump, the flow arises from the revolution of the blades inside the pumping chamber. The relationship between the blood flow rate, blood pressure difference, and the resistance are given by the formula the blood flow rate=pressure difference/ resistance. Through the above equation, the pressure difference and the resistance can be manipulated to achieve the desired flow rate.

Turbulence

Under certain circumstances, blood flow may become turbulent. Because of this, the blood cells will no longer be oriented in a regular fashion toward the centre of a stream as required. The occurrence of turbulence can be estimated using the Reynolds number (Re). The Reynolds number is determined by the equation given below.

Re= vdƿ/Ƞ

In the equation, v is the average velocity of the blood flow, while d is the diameter of the tube. Ƿ is the blood density, and Ƞ is the blood viscosity. Based on the above equation, the fluid velocity, fluid viscosity, and the pump’s dimension determine the turbulence. The turbulent flow of blood results in the development of blood clots. Therefore, when designing blood pumps care should be taken to avoid turbulent flow and consequently blood clotting.

Reliability of blood pump

The above parameters together with the size of the pump and its power supply, affect the reliability of the device in a number of ways. It has been a challenging task for engineers to design a blood pump. During the design process, several considerations are factored in due to the subtle nature of blood.

One of the main issues associated with the use of blood pumps is that it leads to body trauma. The trauma occurs due to the tissues restraining the pump owing to the differential reaction forces and the canals connecting the pump entry and exit to the human heart. Therefore, engineers responsible for the design of these pumps must ensure that the pump functions are reliable as possible. If the reliability of the pump falls below the required standard, the lives of the patients would be at risk.

Another feature that affects the reliability of the pump is the sealing problems. It has been found that the shaft seals produce heat owing to friction. As such, this heat is to be blamed for thrombus formation. Therefore, the pump designers should come up with other materials to replace these seals, as they are not suited for long-term applications.

Another feature that affects the reliability of the pump is that it is not cost effective (Stewart & Hamlin 2010, p. 145). To date, the cost of artificial hearts is very high. The technology used in the design of these devices is to be blamed for the increase in the cost of the equipment. Therefore, if improvements are to be made in the future for the device to function perfectly as the natural heart, the designers should ensure that the device is cost effective.

References

Cartier, R 2005, Off pump coronary artery bypass surgery, Landes Bioscience, Georgetown, Tex.

Parker, S 2006, Pump it up!: respiration and circulation, Raintree, Chicago.

Peto, J 2007, The heart, Yale University Press, New Haven.

Stewart, M & Hamlin, J 2010, Pump it up!: the secrets of the heart and blood, Marshall Cavendish Benchmark, New York.

Click Here To Order Now!