Arterial Vessels and Haemodynamics Flashcards
Which value reflects the driving pressure for blood flow?
Arterial blood pressure.
Which non-cardiac component of the cardiovascular system determines the arterial blood pressure?
The elastic arteries.
Define pulse pressure.
What is the average value for pulse pressure?
- Systolic pressure - diastolic pressure.
- Average of 40mmHg.
What is the equation for mean arterial blood pressure?
((SP-DP) / 3) + DP
How do elastic arteries perform their functions?
1 - During systole, the elastic walls of the elastic arteries distend.
- The distension dampens the pulsatile pressure wave created by systole, ensuring continuous flow (dampening function / Windkessel effect).
2 - The wall of the elastic artery recoils during diastole, creating a driving pressure.
- This increases an otherwise low pressure in diastole, maintaining optimum blood pressure and ensuring flow to the periphery (conduit function).
How does pulse pressure change with age?
Why?
- Pulse pressure increases with age.
- This is because the vessels become less compliant, which causes reduced elastic recoil.
- Reduced elastic recoil causes less distension upon systole, which causes an increased systolic pressure.
- Decreased compliance also leads to a lower diastolic pressure.
What is the equation relating flow, Δ pressure and resistance?
Δ pressure = flow * resistance
What is the equation for resistance to blood flow in a single vessel?
R ∝ (η * L) / (pi * r^4)
Where L = vessel length, η is blood viscosity and r is radius.
What is the relationship between flow and resistance according to Poiseuille’s law?
F ∝ r^4
Derive Poiseuille’s equation.
Poiseuille’s equation: flow = (Δ P * pi * r^4) / (η * L)
Δ pressure = flow * resistance
flow = pressure / resistance
resistance ∝ (η * L) / (pi * r^4)
flow = (Δ P * pi * r^4) / (η * L)
What is intermittent claudication?
- A condition in which cramping pain in the leg is induced by exercise.
- Caused by obstruction of a vessel, e.g. due to atherosclerotic plaques, which reduce the radius and lead to reduced blood flow, causing hypoxia.
List the two types of blood flow through vasculature.
1 - Laminar flow.
2 - Turbulent flow.
Which type of blood flow is the most efficient?
Laminar flow.
Which type of blood flow follows Poiseuille’s law?
Laminar flow.
Where does turbulent flow occur?
List 6 examples of environments where turbulent flow might be present.
- Where flow velocity is high.
1 - At large artery branches.
2 - Pregnancy.
3 - Exercise.
4 - Anaemia.
5 - Valve defects.
6 - Arterial stenosis.
What are Korotkoff sounds?
Murmurs caused by turbulent flow.
How might valve defects cause turbulent flow?
- If the valve leaflets fuse along the commissures, the passage through which blood may pass is narrowed.
- In order to sustain cardiac output through a narrowed valve, the ventricle must eject blood at a higher velocity.
- The velocity increase is achieved by increasing force of contraction (and therefore peak systolic pressure).
- The high velocity of the ejected blood causes turbulent flow.
Why do blood pressure cuffs only allow sounds to be heard in the range of an individual’s systolic pressure / diastolic pressure?
- When the cuff pressure is greater than systolic pressure, blood cannot flow past it as the blood entering the arm can never be higher than the systolic pressure.
- When the cuff pressure falls below systolic pressure but is higher than diastolic pressure, blood can flow, however since the velocity of flow is higher than usual (due to compression from the cuff), turbulent flow occurs, creating Korotkoff sounds.
- When the cuff pressure falls short of diastolic pressure, the artery is no longer malformed, restoring laminar flow, which does not produce Korotkoff sounds.
What is the equation for arterial blood pressure?
Arterial blood pressure = cardiac output * total peripheral resistance.
List 4 factors that contribute to systolic pressure.
1 - Stroke volume.
2 - Aortic / arterial distensibility.
3 - Ejection velocity.
4 - Diastolic pressure of previous beat.
List 2 factors that contribute to diastolic pressure.
1 - Arteriolar resistance.
2 - Heart rate.
List 3 factors that contribute to arteriolar resistance.
1 - Vasoconstriction and vasodilation.
2 - Arteriosclerosis.
3 - Atherosclerosis.
What is the difference between arteriosclerosis and atherosclerosis?
- Arteriosclerosis is the stiffening of an artery wall.
- Atherosclerosis is the narrowing of an artery because of plaque build-up.
How might arterial blood pressure be maintained after standing or during haemorrhage?
How does this response maintain arterial blood pressure?
- By constricting arterioles to multiple organs.
- This will increase total peripheral resistance and therefore increase arterial blood pressure.
