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CVS > Arterial Vessels and Haemodynamics > Flashcards

Arterial Vessels and Haemodynamics Flashcards

1
Q

Which value reflects the driving pressure for blood flow?

A

Arterial blood pressure.

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2
Q

Which non-cardiac component of the cardiovascular system determines the arterial blood pressure?

A

The elastic arteries.

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3
Q

Define pulse pressure.

What is the average value for pulse pressure?

A
  • Systolic pressure - diastolic pressure.

- Average of 40mmHg.

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4
Q

What is the equation for mean arterial blood pressure?

A

((SP-DP) / 3) + DP

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5
Q

How do elastic arteries perform their functions?

A

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).
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6
Q

How does pulse pressure change with age?

Why?

A
  • 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.
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7
Q

What is the equation relating flow, Δ pressure and resistance?

A

Δ pressure = flow * resistance

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8
Q

What is the equation for resistance to blood flow in a single vessel?

A

R ∝ (η * L) / (pi * r^4)

Where L = vessel length, η is blood viscosity and r is radius.

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9
Q

What is the relationship between flow and resistance according to Poiseuille’s law?

A

F ∝ r^4

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10
Q

Derive Poiseuille’s equation.

A

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)

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11
Q

What is intermittent claudication?

A
  • 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.
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12
Q

List the two types of blood flow through vasculature.

A

1 - Laminar flow.

2 - Turbulent flow.

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13
Q

Which type of blood flow is the most efficient?

A

Laminar flow.

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14
Q

Which type of blood flow follows Poiseuille’s law?

A

Laminar flow.

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15
Q

Where does turbulent flow occur?

List 6 examples of environments where turbulent flow might be present.

A
  • Where flow velocity is high.

1 - At large artery branches.

2 - Pregnancy.

3 - Exercise.

4 - Anaemia.

5 - Valve defects.

6 - Arterial stenosis.

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16
Q

What are Korotkoff sounds?

A

Murmurs caused by turbulent flow.

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17
Q

How might valve defects cause turbulent flow?

A
  • 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.
18
Q

Why do blood pressure cuffs only allow sounds to be heard in the range of an individual’s systolic pressure / diastolic pressure?

A
  • 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.
19
Q

What is the equation for arterial blood pressure?

A

Arterial blood pressure = cardiac output * total peripheral resistance.

20
Q

List 4 factors that contribute to systolic pressure.

A

1 - Stroke volume.

2 - Aortic / arterial distensibility.

3 - Ejection velocity.

4 - Diastolic pressure of previous beat.

21
Q

List 2 factors that contribute to diastolic pressure.

A

1 - Arteriolar resistance.

2 - Heart rate.

22
Q

List 3 factors that contribute to arteriolar resistance.

A

1 - Vasoconstriction and vasodilation.

2 - Arteriosclerosis.

3 - Atherosclerosis.

23
Q

What is the difference between arteriosclerosis and atherosclerosis?

A
  • Arteriosclerosis is the stiffening of an artery wall.

- Atherosclerosis is the narrowing of an artery because of plaque build-up.

24
Q

How might arterial blood pressure be maintained after standing or during haemorrhage?

How does this response maintain arterial blood pressure?

A
  • By constricting arterioles to multiple organs.

- This will increase total peripheral resistance and therefore increase arterial blood pressure.

25
Q

What physiological change in the vascular smooth muscle of the vessel walls results in vasoconstriction?

List 3 causes of this physiological change.

A
  • An increase in calcium influx results in vasoconstriction. This is caused by:

1 - Endothelin release in the endothelial cells.

2 - Thromboxane release in the endothelial cells.

3 - PGF release in the endothelial cells.

26
Q

List 2 factors which can increase endothelin release in endothelial cells.

A

1 - Angiotensin II.

2 - Trauma.

27
Q

What physiological change in the vascular smooth muscle of the vessel walls results in vasodilation?

List 5 causes of this physiological change.

A
  • A decrease in calcium influx results in vasodilation. This is caused by:

1 - Nitric oxide release in the endothelial cells.

2 - Adenosine release in the surrounding tissues.

3 - PGE release in the endothelial cells.

4 - PGI2 release in the endothelial cells.

5 - EDHF release in the endothelial cells.

28
Q

List 6 factors which can increase nitric oxide release in endothelial cells.

A

1 - Acetylcholine.

2 - Substance P.

3 - ATP.

4 - Bradykinin.

5 - Thrombin.

6 - Endotoxins.

29
Q

Give an example of a metabolic mechanism of flow control.

A
  • Adenosine is produced in active tissues.
  • Adenosine is a vasodilator.
  • Flow is increased to active tissues by way of adenosine release.
30
Q

What is active / functional hyperemia?

A

The increase in blood flow in response to increased metabolic demands.

31
Q

What is reactive hyperemia?

A
  • The increase in blood flow after the build up of metabolites in a tissue that had an abnormally low flow, e.g. after an obstruction is cleared (such as a blood pressure cuff).
  • This response results in an excessively large flow.
32
Q

Describe the myogenic mechanism for flow autoregulation.

What is the range of pressures for myogenic autoregulation?

A
  • The autoregulatory range is 60-150mmHg for cerebral vessels and 80-200mmHg for kidney vessels.
  • Since flow = pressure / resistance, increased intravascular pressure must be met with increased resistance to keep flow constant.
  • Resistance vessels will therefore vasoconstrict in response to increased intravascular pressure in order to increase resistance.
33
Q

What type of neural innervation is received by vascular smooth muscle?

What is the exception?

A
  • Sympathetic only.

- Only the genitalia and exocrine glands in the head receive both sympathetic parasympathetic innervation.

34
Q

What types of autonomic nerve activity bring about vasoconstriction?

How does this activity change to bring about normal tone and vasodilation?

A
  • Vasoconstriction is brought about by high sympathetic activity.
  • Normal tone is brought about by moderate sympathetic activity.
  • Vasodilation is brought about by decreased sympathetic activity (not increased parasympathetic activity; there is no antagonism with regards to innervation).
35
Q

Which sympathetic receptors are present on vessel walls?

What happens when these receptors are stimulated?

A
  • Alpha 1 receptors are found on all vessels, which cause vasoconstriction when stimulated.
  • Skeletal muscle vessels also have beta 2 receptors, which cause vasodilation when stimulated.
36
Q

What is the difference in binding strength of noradrenaline to alpha 1 receptors compared to beta 2 receptors?

A

Noradrenaline binds to beta 2 receptors much more weakly than it does to alpha 1 receptors.

37
Q

In skeletal muscle, activity of which receptor predominates in response to increased sympathetic nerve activity?

A

Alpha 1 receptor activity predominates over beta 2 receptors.

38
Q

In skeletal muscle, activity of which receptor predominates in response to increased circulating adrenaline?

A

Beta 2 receptor activity predominates over alpha 1 receptors.

39
Q

Describe 2 hormonal mechanisms for regulation of blood flow.

A

1 - The pituitary releases ADH, which binds to V1 receptors on vessel walls to cause vasoconstriction.

2 - The kidneys secrete renin, which converts angiotensinogen into angiotensin I. Angiotensin I is converted into angiotensin II by ACE in the lungs. Angiotensin II binds to angiotensin II receptor type 1 on vessel walls to cause constriction.

40
Q

List the 4 types of control of vasoconstriction and vasodilation (summarise cards 26-40).

A

1 - Endothelial factors.

2 - Local mechanisms (active, reactive and myogenic mechanisms).

3 - Neural mechanisms.

4 - Hormonal mechanisms.

CVS (18 decks)

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