Arterial Vessels and Haemodynamics Flashcards
What are the 2 functions of elastic arteries?
- dampen the pulsatile pressure to ensure continuous flow into the circulation (dampening function, Windkessel effect)
- ensures blood pressure is maintained during diastole (act as tubes to ensure flow to periphery (conduit function)
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
driving pressure
elastic
pulsatile
How is mean ABP calculated?
(SP-DP/3) +DP
How do elastic arteries have a dampening effect?
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
How does ageing affect pulse pressure?
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
- -
- Vessel length L
- Blood viscosity n
- Radius R
R proportional to N xL/R^4
In what two ways can flow through a vessel be described?
Laminar flow
Turbulent flow
What is laminar flow?
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
What is turbulent flow?
Give examples of when it can occur
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
Can you auscultate laminar flow?
No
Only turbulent flow can be heard - Korotkoff sounds and murmurs
Describe the mechanism by which aortic valve stenosis causes a murmur
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
Level of ABP is determined in the elastic arteries and is the driving force for flow
This is determined by:
1.
2.
- blood volume in the arterial system CO
2. resistance to blood flow TPR
In order of importance, what is SP determined by?
- stroke volume
- aortic/arterial distensibility
- ejection velocity
- DP of previous beat
Increases in the following increases SP" - - - -
EDV (preload)
contractility
decreased aortic compliance
increased ejection velocity
What is DP determined by?
x2
- Arteriolar resistance
2. HR
What factors increase DP?
Arteriolar resistance --> vasoconstriction --> arteriosclerosis --> atherosclerosis HR --> a very high HR increases DP
What affect does vasodilatation have on flow?
Vasodilation increases flow
Vasoconstriction and vasodilation of arterioles alter resistance to flow.
Why 4 things is this controlled by?
- endothelial factors
- local mechanisms
- central neural mechanisms
- hormonal mechanisms
- Constriction of arterioles to one organ ……… flow to that organ
- Constriction of arterioles to multiple organs can increase ……. and therefore increase ……..
decreases
TPR
ABP
Explain endothelial control
Lots of factors NO - short acting - decerases Ca2+ --> dilation Endothelin - increases Ca2+ --> constriction
- maybe more
Explain local factors
Metabolic mechanisms
- increased O2 consumption
- increased CO2, H+, adenosine —> vasodilation
Myogenic mechanisms
- reflex vasoconstriction in response to increased intravascular pressure
- auto regulation
What is hyperaemia?
What is functional hyperaemia?
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
Explain central neural mechanisms
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
Explain hormonal mechanisms
ADH –> vasoconstriction. Released when volume goes down, to maintain pressure
Angiotensin II –> vasoconstriction
