Arterial Vessels and Haemodynamics

Question 1

What are the 2 functions of elastic arteries?

Answer 1

1. dampen the pulsatile pressure to ensure continuous flow into the circulation (dampening function, Windkessel effect)
2. ensures blood pressure is maintained during diastole (act as tubes to ensure flow to periphery (conduit function)

Question 2

ABP reflects the …… …….. for blood flow
ABP is determined in ………. arteries
Rhythmic ejection of blood from ventricle leads to ….. pressure in aorta and large arteries

Answer 2

driving pressure
elastic
pulsatile

Question 3

How is mean ABP calculated?

Answer 3

(SP-DP/3) +DP

Question 4

How do elastic arteries have a dampening effect?

Answer 4

During systole the elastic wall of aorta distances (energy stored)
Aortic wall recoils during diastole to propel blood forward (energy released)
Driving pressure sustained during diastole –> continuous blood flow
Pressure wave progressively damped in small arteries

Question 5

How does ageing affect pulse pressure?

Answer 5

Pulse pressure = SP-DP
Compliance of arteries reduces with age
Increased SP = ejection of same or even reduced SV
Decreased DP = reduced elastic recoil
Pulse pressure therefore increases with age

Question 6

• -

Answer 6

1. Vessel length L
2. Blood viscosity n
3. Radius R
   R proportional to N xL/R^4

Question 7

In what two ways can flow through a vessel be described?

Answer 7

Laminar flow

Turbulent flow

Question 8

What is laminar flow?

Answer 8

Normal pattern of flow
Highly efficient
Follow Pouseille’s Law
- `there is an immobile layer, blood layers slip over each other, flow is fastest in the vessel centre

Question 9

What is turbulent flow?

Give examples of when it can occur

Answer 9

occurs where flow velocity is high
inefficient
cannot apply Pousielle’s Law
e.g. at large artery branches, pregnancy, exercise, anaemia, valve defects/arterial stenosis

Question 10

Can you auscultate laminar flow?

Answer 10

No

Only turbulent flow can be heard - Korotkoff sounds and murmurs

Question 11

Describe the mechanism by which aortic valve stenosis causes a murmur

Answer 11

Valve leaflets are fused along commissures
Left ventricle must eject blood at high velocity through narrowed valve to sustain 5L of output per minute
Velocity increase is achieved by increasing force of contraction and peak systolic pressure
Sound internisty increased between systolic and dustolic pressure - more turbulence

Question 12

Level of ABP is determined in the elastic arteries and is the driving force for flow
This is determined by:
1.
2.

Answer 12

1. blood volume in the arterial system CO

2. resistance to blood flow TPR

Question 13

In order of importance, what is SP determined by?

Answer 13

1. stroke volume
2. aortic/arterial distensibility
3. ejection velocity
4. DP of previous beat

Question 14

Increases in the following increases SP"
- 
-
-
-

Answer 14

EDV (preload)
contractility
decreased aortic compliance
increased ejection velocity

Question 15

What is DP determined by?

x2

Answer 15

1. Arteriolar resistance

2. HR

Question 16

What factors increase DP?

Answer 16

Arteriolar resistance 
--> vasoconstriction
--> arteriosclerosis
--> atherosclerosis 
HR --> a very high HR increases DP

Question 17

What affect does vasodilatation have on flow?

Answer 17

Vasodilation increases flow

Question 18

Vasoconstriction and vasodilation of arterioles alter resistance to flow.
Why 4 things is this controlled by?

Answer 18

1. endothelial factors
2. local mechanisms
3. central neural mechanisms
4. hormonal mechanisms

Question 19

• Constriction of arterioles to one organ ……… flow to that organ
• Constriction of arterioles to multiple organs can increase ……. and therefore increase ……..

Answer 19

decreases
TPR
ABP

Question 20

Explain endothelial control

Answer 20

Lots of factors 
NO
- short acting 
- decerases Ca2+ --> dilation 
Endothelin
- increases Ca2+ --> 
constriction 

• maybe more

Question 21

Explain local factors

Answer 21

Metabolic mechanisms
- increased O2 consumption
- increased CO2, H+, adenosine —> vasodilation
Myogenic mechanisms
- reflex vasoconstriction in response to increased intravascular pressure
- auto regulation

Question 22

What is hyperaemia?

What is functional hyperaemia?

Answer 22

Increased blood flow to meet metabolic needs

E.g. when taking blood pressure, no flow, then increased flow when cuff removed due to a build up of metabolites

Question 23

Explain central neural mechanisms

Answer 23

Most vascular smooth muscle has tonic vasomotor tone due to ongoing sympathetic nerve activity.
All vessels including skeletal muscle have alpha 1 receptors (vasoconstriction)
Skeletal muscle also has B2 receptors (vasodilation)
NA binds more strongly to alpha 1 so increased sympathetic activity leads to vasoconstriction.
Adrenaline binds more strongly to B2 so catecholamine release leads to vasodilation

Question 24

Explain hormonal mechanisms

Answer 24

ADH –> vasoconstriction. Released when volume goes down, to maintain pressure
Angiotensin II –> vasoconstriction