16. PHYSICS OF THE CIRCULATION SYSTEM (PART 1)

Question 1

1. What are the three components of the Cardiovascular system?

Answer 1

1. Blood is the vehicle for transport
2. The circulatory system is the distribution system
   - it consists of a series of branches blood vessels
   - blood represents about 7% of our body mass
3. The heart is a four-chambered pump
   - it is composed mostly of cardiac muscles
   - these enable the circulatory flow
   - each section of the heart pumps about 80 mL with
   each contraction

Question 2

2. In Newtonian terms, what kind of fluid is blood?

Answer 2

• it is a Non-Newtonian fluid

Question 3

3. What does the blood solution consist of?

Answer 3

• plasma
• red blood cells
• white blood cells
• platelets

Question 4

4. What does Blood Viscosity increase with?

Answer 4

• it increases with hematocrits

HEMATOCRITS= the volume percentage of red blood cells in blood

Question 5

5. What is the Rate of Deformation of a Newtonian Fluid?

Answer 5

• it is the velocity gradient
• it is proportional to the shear stress

VISCOSITY:
- the constant of proportionality

Question 6

6. What can be said about the shear stress in solid substances?

Answer 6

• it is proportional to the deformation rate

Question 7

7. What variation exists with regards to Newtonian and Non-Newtonian fluids?

Answer 7

• a variation in the shear stress with the rate of deformation

VISCOSITY:
- the slope of a curve at a point
- this is the apparent viscosity at that point

Question 8

8. Blood is a Non-Newtonian fluid, however, we regards it as a Newtonian fluid within this section of studies.
   Why is that?

Answer 8

• Blood behaves with an extreme similarity to a Newtonian Material

Question 9

9. What is a Newtonian Fluid?

Answer 9

IT IS A FLUID WITH:
- a constant viscosity
- zero shear rate at zero shear stress
- the shear rate being directly proportional to the
shear stress

Question 10

10. What is Blood Pressure?

Answer 10

• it is the pressure needed to push blood flow

Question 11

11. What is the Oscillating pressure of blood as it leaves the aorta?

Answer 11

• it has pressures of between 80 mmHg and 120 mmHg
• this is reflected by the Oscillations in blood pressure
  along the major arteries in systemic circulation

Question 12

12. How long does systole last in one cycle?

Answer 12

• it lasts about ⅓ of the cycle

SYSTOLE = a phase of the heartbeat
= when the heart muscle contracts and pumps
blood from the chambers into the arteries

Question 13

13. How do we calculate the weighted sum of blood pressure?

Answer 13

Question 14

14. What is P pulse?

Answer 14

• this is the arterial pulse pressure
• it is the difference in pressure between systole and
  diastole
• this pressure difference is 40mmHg

DIASTOLE= a phase of the heartbeat
= this is when the heart muscle relaxes
= this allows the chambers to fill with blood

Question 15

15. Where does much of the pressure drop within the arterial system?

Answer 15

• it drops within the arterioles
  (the small arteries)
• the capillaries

Question 16

16. What can be said about the blood pressure in the veins?

Answer 16

• it is very low

Question 17

17. What does the Pulmonary System mirror?

Answer 17

• systemic circulation

EXCEPT:
- all the pressures are lower

Question 18

18. What happens when you stand upright?
    (with regards to pressure)

Answer 18

• there is an additional pressure
• p.g.h
• h = the height relative to the heart

Question 19

19. What is the approximate height in the upper arm where the blood measurements are made?

Answer 19

p = 1 060 kg/m³
g = 9.8 m/s²
h = 1m
P (pressure) = 10 400 Pa
= 79 mmHg

Question 20

20. What can be said about the driving pressure difference from the arteries to the veins AT ANY GIVEN HEIGHT?

Answer 20

• it is unchanged

Question 21

21. Why is it not important to consider the pressure change between the arteries and the veins WHEN looking at the pressure changes between the inside and the outside of a vessel?

Answer 21

• the p.g.h is added to both the inside and the outside of the vessel
• the effect of gravity is significant

Question 22

22. How high does the blood pressure at the aorta have to be?

Answer 22

• it has to be high enough to pump the blood to the top of the brain
• this has a height of 40cm
• the pressure drop is about 30mmHg

Question 23

23. What manifestation shows the effect of gravity?

Answer 23

• the potential of fainting when you stand
• the negative effects of standing on your head for long
  periods of time
• the veins in your head are not designed to pump blood
  back to the heart
• your feet would also stop receiving blood
• it is also why varicose veins are worse when you stand
  upright
• this is because blood needs to be pumped up

Question 24

24. What happens when you stand up?

Answer 24

• the volume of blood in the veins in your legs increases
• the pressure in the veins decreases
  (these veins pump blood back to the heart from the leg)
• this decreases the cardiac output
• this decreases the flow of blood to the brain

HOWEVER:
- the reflex constriction of the leg veins makes sure that
the above mentioned rarely happens

Question 25

25. What is the effect of the reflex arteriolar constriction of the veins in the legs?

Answer 25

- it limits the blood pool - it increases the blood flow resistance - this lessens the decrease in arterial blood pressure

Question 26

26. What are the two types of conditions that the mechanical properties of blood vessels can be measured under?

Answer 26

1. THE LENGTH OF THE GIVEN VESSEL IS KEPT CONSTANT - the diameter is measured - this is a result of the distending pressure 2. THE DIAMETER OF THE GIVEN VESSEL IS KEPT CONSTANT - the length is measured - this is because it is stretched longitudinally

Question 27

27. What affects the flow of blood in the arteries?

Answer 27

- the changes in the rate of the heart beat - the volume of blood pumped per beat (stroke volume) - changes in the arteries themselves - they control their diameters - they do this through chemical and neural mechanisms

Question 28

28. Are blood vessels elastic or inelastic?

Answer 28

- they are elastic - these tubes can change their diameter and area - this is based on the pressure and the temperature they are exposed to

Question 29

29. What are the two physical attributes of blood vessels in a steady state?

Answer 29

1. THEY HAVE A RESISTANCE TO BLOOD FLOW - they need a pressure difference along the length of the vessel - this will drive the blood flow 2. THEY HAVE A COMPLIANCE - this is in response to a distending pressure - DISTENDING = swelling caused by pressure from the inside NB: without pressure fluid or tilting of the vessel - no fluid will flow within the vessel

Question 30

30. What is a Rigid Vessel?

Answer 30

- a rigid vessel has a constant volume (V) - this is called a Resistance Vessel - it has only friction present - there is no compliance - the flow rate of this vessel is affected by the pressure drop inside the vessel

Question 31

31. What is an Elastic Vessel?

Answer 31

- a vessel that has no noticeable resistance - this is called a Compliance Vessel - the volume of this vessel is affected by the pressure difference between the inside and the outside of the vessel

Question 32

32. What can be said about real blood vessels?

Answer 32

- they have attributes of both Resistance and Compliance Vessels

Question 33

33. What are three examples of vessels that are similar to Compliance Vessels?

Answer 33

1. the Aorta 2. Large Arteries 3. Large Veins - the pressure drops along these vessels are relatively small

Question 34

34. What are three examples of vessels that are similar to Resistance Vessels?

Answer 34

1. Arterioles 2. Capillaries 3. Venules

Question 35

35. Which vessel is the main site for pressure drops?

Answer 35

- arterioles - this is why the heart needs to pump blood at such high pressures

Question 36

36. How would we mathematically explain the relationship between the pressure inside and outside the blood vessel walls?

Answer 36

▵P = P - Pext - the pressure inside the blood vessels walls (P) is GREATER than the pressure outside (Pext)

Question 37

37. What is the Law of Laplace for hallow cylinders?

Answer 37

T = ▵P x R T = tension ▵P = change in pressure R = the radius of curvature