The Cardiac Output is the volume of blood circulating around the system per minute. ~5 L/min

1. The heart pumps blood into the arteries raising the pressure within them. The high pressure in the arteries forces blood through the microcirculation into the veins where it returns to the heart

2. The left ventricle supplies the systemic circulation with oxygenated blood which returns to the right atrium.

3. The right ventricle forces deoxygenated blood through the lungs which returns oxygenated to the left atrium.

4. The Cardiac Output is the volume of blood circulating around the system per minute. ~5 L/min

5. flow = volume per unit time. velocity = speed of the particles, mean velocity = flow /cross sectional area

6. h Pressure = ρ x g x h Pressure is a scalar quantity where the fluid exerts a force per unit area in all directions Pressure in a liquid system is strongly affected by hydrostatic columns. ρ is the density of the fluid g is the acceleration of gravity h is the distance to the surface of the fluid

7. Millimeters of mercury (mmHg) is the unit of pressure used in medicine. 100 mmHg is the pressure at the bottom of a 100mm high column of mercury. Mercury is 13.6 times denser than water. mmHg is not a true scientific unit.

8. h (4 feet, 5 inches) ρ is the density of the fluid Pressure = ρ x g x h Because Hg is 13.6 times more dense than water, 1360 mm of water makes as much pressure as 100 mm of Hg. g is the acceleration of gravity h is the distance to the surface of the fluid

9. If system is under pressure the hydrostatic pressures are added to that pressure

10. 1 mmHg = 13.6 mm water = 1332 dynes/cm2 = 0.018 psi (pounds/inch2) Blood pressure averages about 100 mmHg or 1.8 psi, or 1,360 mm water 1 atmosphere is 760 mmHg or 14 psi or 32 feet of water). A car tire holds about 30 psi

11. 136 cm Hydrostatic columns exist in the arterial system The shape of the container is not involved; just the vertical distance

12. Pressure differences causes fluid to flow through tubes with a parabolic velocity profile. Fluid flows in an infinite number of concentric lamina (like a telescope). Slow ones are at the periphery and fast ones in the center

13. The outermost lamina next to the wall has zero velocity. Viscosity (η) is the property of a fluid to resist motion of the molecules (lamina) relative to one another. Pressure pushes each concentric lamina slightly faster that the one surrounding it so the fastest velocity is in the center.

14. The difference in velocity between adjacent concentric lamina (shear) causes the fluid to resist flow through the tube. The resistance is between lamina not between the fluid and the wall!

15. The average velocity of the fluid is exactly ½ of the peak velocity. The peak velocity can be calculated by multiplying the mean velocity (flow/x-sectional area) times 2.

16. Laminar flow minimizes (but does not eliminate) friction which occurs because viscosity still resists movement between lamina

17. R P in P out L How can we calculate flow through a tube? Poiseuille’s equation ! (Pronounced “pwas air”) Jean Louis Poiseuille (1799 - 1869

18. F = η Poiseuille’s equation You can suck Coke up a straw easier than a milk shake (viscosity term).

19. F = Rη Poiseuille’s equation A milk shake is easier to drink with a large diameter straw than a small diameter straw (radius term)

20. F = R · ΔPη Poiseuille’s equation The harder you suck the more drink you get (pressure term)

21. F = R · ΔP L · η Poiseuille’s equation The longer the straw the more difficult it is to drink (length term)

22. R P in P out F = π · R · ΔP 8 · L · η L Poiseuille’s equation We need an “8” and a “π” just because we do (geometric term)

23. R P in P out F = π · R4· ΔP 8 · L · η L Poiseuille’s equation The radius is to 4th power (not squared like you would expect).

24. R P in P out F = π · R4 · ΔP 8 · L · η L Doubling the radius increases flow 16 times (24 = 16). Small changes in a blood vessel’s radius have a big effect on flow.

25. V1 In electrical circuits current (I) flows through a resister (R) in proportion to the voltage difference (ΔV) across the resistor. (Ohm’s Law) I = ΔV / R I If you know any two you can calculate the third R ΔV = I x RR = ΔV / I It also works for fluid flow F = ΔP / RΔP = F x RR = ΔP / F V2

26. Where F = π · R4 · ΔP 8 · L · η R = 8 · L · ηπ · R4 F = ΔP / R 1/R The resistance of the vessels changes with changes in radius.

27. R = 8 · L · ηπ · R4 If the pressure of the fluid is doubled we can keep the flow rate the same by doubling the resistance of the tube

28. Because the vascular system is composed of millions of tiny tubes calculating the resistance of each one is really not practical. Rather we usually measure the flow and ΔP across an organ and calculate the resistance. Resistances calculated by that method are usually reported in peripheral resistance units (PRU). 1 PRU = 1 mmHg/ml/sec.

29. For series circuits simply add the resistances to get the total resistance: Rtotal = R1 + R2 + R3 .....

30. ΔP = F · Rtotal F · Rtotal must equal the total pressure drop across the entire circuit.

31. ΔP = F · R1 The pressure drop across an individual resistor is the flow times its resistance.

32. R total = 130 130 > 100 > 25 > 5 The total resistance must be bigger than any individual resistance

33. Arteries, arterioles, capillaries, and veins are in series with each other.

34. For parallel circuits you must add reciprocals: 1 = 1 + 1 + 1 ...... Rtotal R1 R2 R3

35. Each leg experiences the total pressure Each additional leg provides an alterative route through the system and thus lowers the resistance.

36. R total = 4 100 > 25 > 5 > 4 The total resistance must be smaller than any single resistance. The answer is 4, (not ¼ ). Don’t forget to turn the answer over!

37. One artery feeds many parallel capillaries.

38. Thevenin’s equivalent Any combination of resistors…….. can be reduced to a single equivalent resistance

39. Thevenin’s equivalent

40. Thevenin’s equivalent

41. Thevenin’s equivalent

42. Thevenin’s equivalent

43. Thevenin’s equivalent

44. Thevenin’s equivalent

45. Total peripheral resistance (TPR) gives the total resistance of the systemic circulation. TPR = AOP/CO Systemic TPR is about 5 times pulmonary TPR. That causes Aortic pressure to be about 5 times higher than pulmonary pressure

46. Where F = π · R4 · ΔP 8 · L · η R = 8 · L · ηπ · R4 F = ΔP / R The resistance of the vessels also includes the viscosity.

47. R = 8 · L · ηπ · R4 Plasma Water The hematocrit refers to percentage of the blood volume that is made up of red blood cells. RBC’s increase blood viscosity and thus vascular resistance Red cells carry most of the blood’s oxygen

48. Polycythemia Increasing the hematocrit increases blood viscosity in a non-linear way. Patients with polycythemia have poor oxygen delivery because flow falls more than oxygen content is increased.

49. Polycythemia At a low hematocrit (anemia) low viscosity causes a high blood flow but oxygen delivery is poor because the blood oxygen content is so low.

50. Blood appears to get less viscous as the tube diameter decreases. This is called the Fahraeus-Lindquist effect