Haemodynamics: Arteries

Question 1

What is Haemodynamics?

What are the key factors?

Why does an effect in one area of the CVS affect another are?

Describe the distribution of blood?

Answer 1

• The relationship between blood flow, blood pressure, and resistance to flow.
• Force, Work (ejection), Pressure differences, Compliance, Resistance, Flow, Velocity
• CVS is a closed system. So, reducing blood flow to one area will change the
  blood flow to other areas.
• Most of the blood is in venous system, which acts like a reservoir (low pressure). Can be used to ↑CO according to Starling’s Law (↑EDV).

Question 2

What is:
Darcy’s Law? What is the equation?

Bernoulli’s Law? What is the equation?

Answer 2

• The role of pressure energy in blood flow: Flow = (Arterial pressure - CVP) / TPR
• The role of pressure, kinetics, and potential energies in blood flow: Flow = Pressures + Kinetic + Potential

Question 3

Define:
Blood flow

Perfusion

Velocity of blood flow

Answer 3

• Volume of blood flowing per unit of time (ml/min)
• Blood flow per given mass of tissue (ml/min/g)
• Blood flow divided by the cross sectional area of the vessel (cm/s)

Question 4

What’s the relationship between blood flow and velocity?

Answer 4

Volume flow = Velocity x Area

Velocity in the aorta is high, and the branching of arteries slows velocity - due to ↑Cross-sectional area = ↓Blood flow. Velocity is slowest in capillaries, but increases when veins come together.

Question 5

Describe the 3 patterns of blood flow

LOOK AT DIAGRAMS!

Answer 5

1. Laminar flow - occurs in most vessels:
   There is 0 velocity at the walls (due to molecular interactions with it). Maximum Velocity at centre of vessel. This moves RBCs to the centre to speed up its movement.
2. Turbulent flow - occurs in ventricles, aorta, and atheroma:
   Blood flow isn’t linear and smooth. It’s in whirlpools due to the changes in velocity.
3. Bolus flow - occurs in capillaries:
   RBCs have a larger diameter than the capillaries, so plasma columns are trapped between RBCs. This causing uniform velocity and very low resistance.

Question 6

What determines change from laminar to turbulent flow?

Answer 6

• Reynold’s number (Re): when it goes over a certain value e.g. during bruits, ejection murmurs.

Question 7

How is pressure generated in the heart?

What occurs to arterial pressure along the systemic pathway?

What affects arterial BP?

What 4 interactions are involved in arterial blood pressure?

LOOK AT PRESSURE WAVEFORM GRAPH!

Answer 7

• By the left ventricle contracting
• It decreases
• CO, Properties of arteries, Peripheral resistance, Blood viscosity.
• Interactions between Systolic pressure, Diastolic pressure, Pulse pressure, Mean blood pressure.

Question 8

What is the role of the aorta in producing the arterial blood pressure?

LOOK AT PICTURES!!

Answer 8

During LV ejection:
• Most of SV is stored in aorta as it expands
• Energy is stored in stretched elastin fibres

During LV diastole:
• Energy is returned to blood as the walls of aorta contract
• This sustains the diastolic blood pressure and blood flow even when heart is relaxed

*Elastic recoil of aorta helps propel blood into circulation

Question 9

What is Pulse pressure?

What does it tell us? What equation is used?

Describe what happens at the 6 parts of the arterial pressure graph

LOOK AT GRAPH!

Answer 9

• Pulse pressure = Systolic pressure - Diastolic pressure (felt at pulse points in body).
• About SV and arterial compliance:
  Pulse pressure = SV / Compliance
• 1. Ejection
     
     2. Peak systolic
     3. Systolic decline
     4. Closure of aortic valve
     5. Diastolic RUN-OFF
     6. Peak diastolic

Question 10

What happens to pulse pressure, stoke volume and compliance during exercise?

LOOK AT GRAPH!

Answer 10

↑SV = ↑Stretch of arteries = ↓Compliance = ↑Systolic and Pulse pressures

Question 11

What happens to pulse pressure, stoke volume and compliance during exercise in the elderly?

LOOK AT GRAPH!

Answer 11

With age, arteries get stiffer = ↓Compliance.

↑SV = Disproportional ↑ of Systolic and Pulse pressures - arteries can’t stretch as much and the systolic pressure isn’t increased as much.

Age increases stiffness of vessels, so a large pulse pressure is present throughout the arterial tree.

Question 12

How does Aortic Stenosis and Regurgitation affect the pulse pressure graph?

LOOK AT GRAPHS!

Answer 12

Aortic Stenosis – narrowing of valve:
Narrowing of exit from heart, Slower upstroke, and Smaller peak, which indicates poorer ejection.

Aortic Regurgitation - leaky valve:
Fast upstroke, Larger peak, and Poor diastolic run-off, which indicates blood entering aorta/ventricles during diastole.

Question 13

What is the mean arterial BP?

What controls it?

LOOK AT GRAPH!

Answer 13

• Is the Diastolic pressure + 1/3 Pulse pressure!

- Age, Disease, Distance along systemic pathway, Blood volume, Exercise, Emotion, Wake/Sleep