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Physiology 1 : cardiovascular > Principles of Haemodynamics > Flashcards

Principles of Haemodynamics Flashcards

1
Q

Define Haemodynamics:

A

Literally means ‘Blood Movement’.

→Haemodynamics can be defined as the relationship between blood flow, blood pressure and resistance to flow.

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2
Q

What are factors that increase blood flow?

A

Factors that INCREASE blood flow:

  1. Force: Cardiac contraction.
  2. Work: Isovolumetric contraction / ejection.
  3. High Pressure: In aorta.
  4. Compliance: Arterial stretch.
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3
Q

Where is the majority of the blood found?

A

In the venous system.

It acts like a low pressure reservoir system.

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4
Q

What is one key feature of the CVS?

A

It is a CLOSED SYSTEM:
→ Whatever happens in one part will affect another part.
→ Reduced blood flow in one area increases the pressure upstream.
→When flow is altered in one area it has a knock on effect on the entire CVS.

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5
Q

What is the venous reservoir used for and how?

A

→Can be used to increase cardiac output.

(Starling’s Law):
→If more blood flows into the heart there will be more stretch of the ventricles.
→There will be a greater energy of contraction.
→And thus a higher cardiac output.

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6
Q

What is Darcy’s Law

A

→It takes into account the role of pressure energy into blood flow.

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7
Q

What is the Darcy’s Law equation?

A

Q = P1 – P2/R

Q = Flow 
P1-P2 = pressure difference 
R = resistance to flow
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8
Q

What is Darcy’s Law equation for flow in the entire CVS?

A

Flow = (Pa- CVP)/TPR

Pa = Arterial pressure 
CVP = Central venous pressure
TPR = Total peripheral resistance
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9
Q

What is Bernoulli’s Law?

A

→ Equation that takes into account the role of pressure, kinetic and potential energies in blood flow.

  • An increase in the speed of a fluid occurs simultaneously with a decrease in pressure.
  • Or a decrease in the fluid’s potential energy.
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10
Q

What is Bernoulli’s equation?

A

Flow = Pressure (PV) + Kinetic [(ρV^2)/2] + potential (ρgh)

Kinetic Energy: Momentum of Blood
Potential energy: effect of gravity
ρ = fluid mass
P = pressure
V = velocity
h = height
g = acceleration due to gravity
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11
Q

What is blood flow?

A

The volume of blood flowing in a given time (ml/min).

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12
Q

What is blood perfusion?

A

Blood flow per given mass of tissue (ml/min/g).

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13
Q

What is the velocity of flow?

A

Blood flow divided by the cross sectional area through which the blood flows (cm/s).

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14
Q

Describe the changes in velocity as the blood flows through the vasculature?

A
  1. Initially velocity of blood flow high in aorta.
  2. Decreased velocity due to branching of the arteries.
  3. Velocity reaches its slowest at capillaries as extensive branching and large cross sectional area.
  4. Velocity increases again as veins come together.
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15
Q

Why does the velocity of blood flow change?

A

Due to an increased cross sectional area.

Cross-sectional area brings blood flow and velocity together.

The greater the cross-sectional area the slower the flow.

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16
Q

What are the 3 patterns of blood flow?

A
  1. Laminar.
  2. Turbulent.
  3. Bolus.
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17
Q

Where is Turbulent flow found?

A

→Ventricles (mixing).
→Aorta (peak flow).
→Atheroma (bruits).

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18
Q

Describe Laminar flow:

A

→The blood flow is in concentric shells with:
→ Near zero velocity near the walls.
→Maximum velocity near the centre.

→This moves the RBCs towards the centre and speeds up blood flow through narrow vessels.

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19
Q

Describe Bolus flow:

A

→ RBCs have a larger diameter than the diameter of the capillaries so they move in a single file line.

→There are plasma columns trapped between RBCs.

  • Here there is:
    →Uniform velocity.
    → Little internal friction.
    →Very low resistance.
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20
Q

Where is Laminar Flow found?

A

Arteries.
Arterioles.
Venules.
Veins.

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21
Q

Describe Turbulent Flow:

A

→Blood does not flow linearly and smoothly in adjacent layers.

→Whirlpools, eddies and vortices due to the increased pressure and velocity or obstructions.

22
Q

Where is Bolus Flow found?

A

Capillaries.

23
Q

What is Reynold’s Number?

A

Number used in fluid mechanics to indicate whether fluid flow past a body or in a duct is steady or turbulent.

24
Q

What does Reynold’s Number describe?

A

Describes what determines the change from laminar to turbulent.

25
Q

What are bruits?

A

Abnormal sound generated by turbulent flow of blood in an artery due to either:

  • An area of partial obstruction.
  • Or a localized high rate of blood flow through an unobstructed artery.
26
Q

What is the equation used to derive Reynold’s Number?

A

Re = ρVD/μ

(density x velocity x diameter) / viscosity

27
Q

How does Reynold’s number identify turbulence?

A
  • Turbulence occurs when Reynold’s number exceeds a critical value (>2000).
  • E.g bruits, ejection number, increased blood velocity
28
Q

Where is blood pressure the highest?

A

→Highest in aorta.

29
Q

What is the blood pressure during systole?

A

→120 mmHg.

30
Q

What is the blood pressure during diastole?

A

→80mmHg.

31
Q

What is the equation for blood flow?

A

Flow = Arterial Blood Pressure/Total Peripheral Resistance

32
Q

What generates blood pressure?

A

Contraction of the Left Ventricle in Systole.

33
Q

What are the 4 factors that affect arterial blood pressure?

A
  1. Cardiac output
  2. Properties of arteries
  3. Peripheral resistance
  4. Blood viscosity
34
Q

What are the four pressure relationships?

A

SYSTOLIC PRESSURE: pressure when ejecting.

DIASTOLIC PRESSURE: pressure when relaxing.

PULSE PRESSURE: difference between diastolic and systolic pressure.

MEAN BLOOD PRESSURE: average pressure.

35
Q

What is the role of the Aorta/large arteries in arterial blood pressure?

A

→Recoil of elastic fibres of the aorta and large arteries helps to propel the blood into the circulation.

36
Q

Describe the action of the Aorta during Left Ventricle Ejection:

A

→60-80% of stroke volume is stored in the aorta and arteries as these structures expand.

→Energy stored in stretched elastin.

37
Q

Describe the action of the Aorta during Left Ventricle Diastole:

A

→Energy is returned to the blood as the walls of the aorta and arteries contract

→This sustains diastolic blood pressure and blood flow when the heart is relaxed

38
Q

What is Pulse Pressure?

A

→Pulse pressure is what the finger senses for example at the wrist (radial artery).

39
Q

What does Pulse Pressure tell us?

A

→It tells us about the stroke volume and the arterial compliance (stretchiness).

40
Q

Equation for Pulse Pressure:

A

→Pulse pressure = stroke volume / compliance

41
Q

How does age affect arterial pulse pressure?

A

→Age increases the stiffness of vessels - particularly the aorta.

→A large pulse pressure is present throughout the arterial tree.

42
Q

What is the relationship between distance from the aorta and pressure?

A

→The further a vessel is from the aorta the higher the pulse pressure.

43
Q

What does tapering of vessels do?

A

→Increases the stiffness of distal arteries.

44
Q

What happens to the pressure at arterioles?

A

→At arterioles the pulse pressure disappears due to drop in velocity.

45
Q

What is Aortis Stenosis?

A

→Narrowing of the aortic valve.
→Narrowing of exit from heart, slower upstroke, smaller peak.
→Indicates poor ejection.

46
Q

What is Aortic Regurgitation?

A
  1. Leaky aortic valve
  2. Fast upstroke, larger peak, poor diastolic run off
  3. Indicates blood entering aorta/ventricles during diastolic.
47
Q

How do you calculate mean BP?

A

Diastolic pressure + 1/3 [pulse pressure]

48
Q

What controls mean blood pressure?

A
  1. Age
  2. Disease
  3. Blood volume - SV, CO.
  4. Exercise - SV, CO.
  5. Emotion - stress, anger, fear, apprehension, pain.
  6. Wake/ Sleep - decrease in BP 80/50 mmHg.
49
Q

What do changes in pulse pressure indicate?

A

Changes in pulse pressure indicate changes in stroke volume.

50
Q

What are factors that decrease blood flow?

A

Factors that DECREASE blood flow:

  1. Resistance: Arterioles.
  2. Flow velocity: Slowing down blood flow in capillaries.
  3. Low Pressure: in veins.
51
Q

What is the equation for volume flow?

A

→ Volume flow (Q) = velocity (v) x area (a)

Physiology 1 : cardiovascular (18 decks)

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