1. Hemodynamics

2. Hemodynamics…
The study of the movement of blood and of the forces concerned.

3. Physical Characteristics of Circulation

5. Functional parts of the circulation…
Arteries:
Transport blood.
Strong vascular wall.
Rapid flow of blood.
Arterioles:
Control valves.
Strong muscular wall.

6. Cont… Capillaries: Venules:
Exchange fluid, nutrients, electrolytes & other substances.
Very thin wall.
Venules:
Collect blood from capillaries.
Coalesce into larger veins.

7. Cont… Veins: Transport blood from tissues back to heart.
Major reservoir of blood.
Thin muscular wall.
Low pressure.

8. Volumes of blood in different parts of circulation

9. Cross sectional areas & velocities of blood flow
cm2
2.5
Aorta 20
Small arteries 40
Arterioles
2500
Capillaries
250
Venules 80
Small viens 8
Venae Cavae

10. Cont…
Velocity of blood flow is inversely proportional to cross sectional area.
Under resting conditions:
33 cm/sec in aorta.
0.3 mm/sec in capillaries.

11. Pressure in various portions of circulation

12. Biophysical consideration: interrelationships among pressure, flow and resistance

13. Relations among P,R & Q
Pressure gradient.
Vascular resistance.

14. Cont…
Ohm’s law:

15. Blood flow
Quantity of blood that passes a given point in the circulation in a given period.
5000 ml/min

16. Laminar flow of blood
Parabolic velocity profile during laminar flow

17. Cont… Critical velocity:
Laminar flow occurs up to a certain critical velocity.
At or above this critical velocity, flow is turbulent.

18. Cont… Turbulent flow: Reynold’s number:
Blood flow in all directions and continually mixing with the vessel.
Reynold’s number:
The measure of the tendency for turbulence to occur.

19. Reynold’s Number Reynold’s Number = vpD/u
p is the weight-density of the fluid
u is the dynamic viscosity of the fluid
v is the velocity of the fluid flow
D is the diameter of the tube

20. Cont… If Re < 2000  flow is not turbulent.
If Re > 3000  turbulence is almost always present.

21. Conditions where turbulent flow may occur
When rate of blood flow becomes too great.
Obstruction in a vessel.
Sharp turn.
Viscosity of blood is low.

22. Measuring blood flow Electromagnetic flowmeter.
Ultrasonic Doppler flowmeter

23. Electromagnetic flowmeter

24. Blood pressure
The force exerted by the blood against any unit area of the vessel wall.
Measured in:
mmHg (using mercury manometer).
Cm H2o.
1 mmHg = 1.36 cm H2o

25. Methods for measuring blood pressure
Mercury manometer.
High fidelity method.

26. Mercury manometer

27. High fidelity method: electronic pressure transducers

28. Resistance The impediment to blood flow in a vessel.
Can’t be measured.
Instead calculated from measurement of blood flow & pressure difference.

29. Cont…
Unit of resistance: peripheral resistance unit.

30. Total peripheral resistance & total pulmonary resistance
Strong constriction 4 PRU
Strong dilation 0.2 PRU
Mean Rt arterial P= 16 mmHg
Mean Lt atrial P= 2 mmHg

31. Conductance of blood & resistance
Conductance: a measure of blood flow through a vessel for a given change in pressure.
ml/ sec/ mmHg.
The reciprocal of resistance.

32. Changes in diameter & conductance
Conductance of a vessel increase in proportion to the forth power of the diameter.

33. Cont… Poiseuille’s law:
Note: Q is directly proportional to the forth power of radius, demonstrating that diameter of a blood vessel plays the greatest role.

34. Importance of forth power law in determining arteriolar resistance
Arteriolar respond to nervous signals or local tissue signals.
Turning off blood flow or increase flow.

35. Effect of blood hematocrit & viscosity on vascular R & Q
Viscosity: the friction developed between RBCs as they slide over each other during flow of blood.
An important factor in Poiseuill’s law.

36. Greater resistance to flow
Cont…
Greater viscosity
Greater resistance to flow
The less the flow

37. Hematocrit
The percentage of blood volume occupied by erythrocytes as they are packed down in a centrifuged blood sample.

38. Effect of hematocrit on blood viscosity

39. Effects of pressure on vascular resistance & tissue Q

40. Vascular Distensibility & Function of the Arterial & Venous System

41. Vascular distensibility
Normally expressed as the fractional increase in volume for each mmHg rise in pressure.
When a vessel being distensible it means it can swell out by pressure from within.

42. E.g….
Distensibility = 0.1 per mmHG or 10 %/ mmHg

43. Difference in distensibility between arteries & veins
Walls of arteries are thicker than veins.
Veins are 8 х as distensible as arteries.

44. Vascular compliance
The total quantity of blood that can be stored in a given portion of the circulation for each mmHg rise in pressure.
It’s a measure of how easily the structure can be stretched.

45. Cont… Compliance = distensibility x volume
e.g: veins are 24x more compliant than arteries
(8x as distensible x 3x as great volume) = 24

46. Compliance and distensibility are quit different
Highly distensible vessel/ slight volume
Less compliance
Less distensible vessel/ large volume
More compliance

47. Volume- pressure curve of the arterial and venous circulation

49. Delayed compliance ( stress- relaxation) of vessels

51. Arterial pressure palsation

52. Cont… Factors affecting pulse pressure: Stroke volume.
Compliance of arterial tree.

53. Less compliance
Greater rise in pressure for a given stroke volume of blood pumped into the arteries

55. Damping of pressure pulse

56. The cause of damping of pressure pulse
Compliance of the vessels
Resistance to blood movement in vessels

57. Clinical methods for measuring blood pressure
Auscultatory method (sphygmomanoneter)

58. Auscultatory method
Sphygmomanometer
Sounds heard

59. Normal arterial blood pressure

60. Veins and their function

61. Central venous pressure (CVP)
Venous pressure as measured at Rt atrium.
Measured by means of a catheter .

62. CVP and right atrial pressure
Anything that affect Rt atrial pressure usually affects venous pressure everywhere in body.

63. Ability of the Ht to pump blood out of Rt atrium
Tendency for blood to flow from peripheral vessels back to Rt atrium
Regulation of Rt atrial pressure

64. Cont… Normal Rt atrial pressure = 0 mmHg
Can rise to mmHg (abnormal conditions).
Can fall to -3 to -5 mmHg.

65. Measurment of venous & Rt atrial pressure
Venous pressure
Rt atrial pressure
By inserting a syringe needle
Inserting a catheter through veins into Rt atrium

66. Venous resistance and peripheral venous pressure

67. Peripheral small veins :
4-7 mmHg >
Rt atrial pressure

68. Effect of high atrial pressure on peripheral venous pressure
when Rt atrial pressure increase above 0 mmHg.
When Rt atrial pressure > 4-6 mmHg.

69. Hydrostatic pressure and venous pressure

70. Hydrostatic pressure affect !!arterial pressure
1mmHg= 13.6 mm H2o
Hydrostatic pressure affect !!arterial pressure

71. Venous valves and venous pump: their effect on venous pressure

72. Importance of valves.
Arrangement of valves.
Effect of movement of the legs.