1. Blood Pumps Pressure/Flow/Resistance Brian Schwartz, CCP Perfusion I September 16, 2003

2. Blood Pumps Purpose of Blood Pumps Ideal Blood Pump Types of Blood Pumps Most Commonly Used Pumps Types of Blood Flow Other Blood Pumps Used

3. Development of Blood Pumps To replace the beating heart during heart surgery They propel blood and other physiologic fluids throughout the extracorporeal circuit; which includes the patient’s natural circulation as well as the artificial one

4. The Ideal Blood Pump Move volumes of blood up to 5.0 L/Min Must be able to pump blood at low velocities of flow All parts in contact with blood should have smooth surface Must be possible to dismantle, clean and sterilize the pump with ease, and the blood handling components must be disposable

5. The Ideal Blood Pump (continued) Calibration should be easy, reliable, and reproducible Pump should be automatically controlled; however, option for manual operation in case of power failure Must have adjustable stroke volume and pulse rate

6. FYI The average human heart can pump up to 30 liters of blood per minute under extreme conditions. In the operating room setting this is not necessary due to may reasons: –patient is asleep –patient is given muscle relaxants –patient metabolic rate is greatly reduced –patient is cooled during CPB

7. Types of Blood Pumps Kinetic Pumps –Centrifugal pumps Positive Displacement Pumps: –Rotary Pumps –Reciprocating Pumps

8. Centrifugal Pumps The pumping action is performed by the addition of kinetic energy to the fluid through the forced rotation of an impeller

9. Centrifugal Pumps Designed with impellers arranged with vanes or cones Centrifugal pumps are magnetically driven and produce a pressure differential as they rotate It is the pressure differential between the inlet and outlet that causes blood to be propelled

10. Positive Displacement Pumps This type of pump moves blood forward by displacing the liquid progressively, from the suction, to the discharge opening of the unit

11. Positive Displacement Pumps (continued) Rotary Pumps –Roller Pumps –Screw Pumps Reciprocating Pumps –Pistons –Bar Compression –Diaphragm

12. Rotary Pumps –use rollers along flexible tubing to provide the pumping stroke and give direction to the flow Archimedean Screw Pumps –a solid helical rotor revolving within a stator with different pitches so the blood is drawn along the threads

13. Rotary Pumps (continued) Multiple Fingers –the direction of flow is produced by a series of keys that press in sequence against the tubing

14. Reciprocating Pumps Pistons –this pump uses motor driven syringes that are equipped with suitable valves, delivering pulsatile flow –limited to low output capacity Bar Compression –blood moves from the alternate compression and expansion of the tube or bulb between a moving bar and a solid back-plate

15. Reciprocating Pumps (continued) Diaphragm Pumps –with a flat diaphragm or finger shaped membrane made of rubber, plastic, or metal, blood is propelled forward Ventricle Pumps –a compressible chamber mounted in a casing and are activated by displacement of liquid or gas in the casing

16. Two Most Common Pumps Today Roller Pump –Advantages Occlusive, therefore if power goes out the arterial line won’t act as a venous line Out put is accurate because it is not dependent of the circuits resistance (including the patients resistance) –Disadvantages Can cause large amounts of damage to blood (hemolysis) if over-occluded

17. Two Most Common Pumps Today (continued) Centrifugal Pump –Advantages Reduced hemolysis No cavitation No dangerous inflow/outflow pressures Air gets trapped in pump No need to calibrate

18. Two Most Common Pumps Today (continued) Centrifugal Pump –Disadvantages Causes over-heating Over heating promotes clotting Difficult to de-air If power goes out, arterial line acts like a venous line

19. Roller Pump

20. Two Types of Perfusion Pulsatile Flow (simulates the human heart) –Decreases peripheral resistance –Increases urinary flow –Better lymph formation –Increases myocardial blood flow –Need 2.3 times more energy to deliver blood in a pulsatile manner than with non- pulsatile flow

21. Two Types of Perfusion (continued) Non-Pulsatile Flow –Simply means continuous flow

22. Various Opinions on Pulsatile Flow Advocates –It simulates the beating heart, aiding in preserving capillary perfusion and cell function –With the extra energy produced with pulsatile flow, we can avoid the closing down of the capillary beds.

23. Various Opinions on Pulsatile Flow (continued) Opponents –Pulsatile flow is a more complex procedure for minimal benefits –Capillary Critical Closing Pressure: (although never seen under microscope) The belief that when the pressure in the capillary system goes below a certain point the capillaries will close…reducing the gas exchange between the blood and the tissues

24. Flow, Pressure and Resistance Blood Flow: defined as the movement of blood flow through the body, or in our case, the extracorporeal circuit Pressure: defined as the force vector that is exerted at a 90 degree to that of blood flow Resistance: the force vector opposite to that of pressure

25. The Relationship Between Pressure, Flow and Resistance Flow = Pressure / Resistance Resistance = Pressure / Flow Pressure = Flow X Resistance

26. Laminar Flow Definition: Referring to blood flow, where all the layers run parallel to the walls of the blood vessels or tube

27. Reynold’s Number An equation that enables us to determine whether blood flow is laminar or turbulent R.N = 2 (fluid density)( average velocity)(r) (fluid viscosity) If R.N. < 2000 flow is laminar If R.N. > 3000 flow is turbulent If R.N. between 2000 and 3000 flow unstable

28. Reynold’s Number (continued) Blood acts as a Newtonian fluid, one that has a constant viscosity at all velocities A thixotropic fluid : the viscosity is altered by changing velocities

29. Viscosity Another important factor that effects the flow of blood Viscosity = Shear Stress / Shear Rate

30. Poiseuille’s Law Expresses how different variables effect flow. The most notable variable is radius of the vessel or tube. Flow = (Pressure gradient)(3.14)(radius 4)  8 (viscosity)(length)

31. Resistance The main source of resistance is the arterioles. This resistance comes after the pressure source (the heart) giving up peripheral resistance TPR = MAP/F TPR= Sum of all factors effecting the resistance to flow

32. Resistance (continued) SVR= PA - PV / Q PA= MAP PV= RAP Q= Flow Rate SVR= (MAP-CVP/C.O.) X 80

33. Pressure When the heart contracts and the pressure rises, the highest point is called systolic pressure When the heart relaxes and the aortic pressure reaches the lowest point.. this is called diastolic pressure Mean arterial pressure = SP/DP

34. Pressure (continued) Because vessels aren’t normally rigid, rather they are flexible, you will see a nice rise in the arterial wave form. If the aorta, the most flexible vessel, is rigid, the systolic pressure would rise sharply. (A good diagnostic indicator)

35. Resistance The main source of resistance is the arterioles Viscosity = Shear Stress / Shear Rate F= (P1-P2) X 3.14 X r4/8L X Viscosity