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SGUL - Physiology 1 > Principles of Haemodynamics > Flashcards

Principles of Haemodynamics Flashcards

1
Q

What are the key parameters considered in haemodynamics?

A
  • Force: Cardiac contraction
  • Work: Isovolumetric contraction/ ejection
  • Pressure: Difference between different vessels
  • Compliance: Atrial stretch
  • Resistance: In arterioles
  • Flow velocity: Slowing down blood flow in capillaries
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2
Q

What is haemodynamics?

A

The relationship between blood flow, blood pressure and resistance to flow

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3
Q

Is the CVS an open or closed system?

A

Closed

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4
Q

What is the main effect of the CVS being a closed system?

A
  • Change in one part of the system impacts other parts of the system
  • Reduced blood flow in one area causes changes in flow in other areas by reducing upstream pressure
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5
Q

How many capillary beds normally does blood go through?

A

1

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6
Q

What is it called when blood goes through 2 capillary beds?

A

Portal system

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7
Q

Where is majority of the blood found in the CVS?

A

Veins/venous system

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8
Q

How does venous blood affect cardiac output?

A
  • Can increase cardiac output ( RECAP - Starling’s law)
  • Have a thin muscle layer and contract slightly
  • Upon contraction, send more blood back into the heart
  • More blood moves into arterial circulation
  • Therefore increases cardiac output
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9
Q

What is Darcy’s law of haemodynamics?

A

Flow = (P1 - P2)/ TPR
P1 - P2: difference in pressure (arterial pressure - CVP)

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10
Q

What is Bernoulli’s law of haemodynamics?

A

Flow = Pressure (P) + Kinetic (ρV^2/2) + Potential (ρgh)
ρ = Fluid mass
P = pressure
V = velocity
h = height
g = acceleration due to gravity

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11
Q

In Bernoulli’s Law of haemodynamics, what does kinetic energy refer to?

A

Momentum of blood

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12
Q

In Bernoulli’s Law of haemodynamics, what does potential energy refer to?

A

Effect of gravity

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13
Q

What is blood flow?

A

Volume of blood flowing in a given time (ml/min)

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14
Q

What is perfusion?

A

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

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15
Q

What is velocity of blood flow?

A

Speed of blood flow (cm/s)

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16
Q

What is velocity of blood flow affected by?

A

Changes in cross-sectional area of vessels

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17
Q

RECAP - Why is blood velocity at the aorta high?

A
  • Only one aorta through which cardiac output passes
  • This aorta has a relatively low cross sectional area ∴ velocity is high
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18
Q

RECAP - As the blood spreads out into other arteries from the aorta, there is a reduction in velocity. Suggest why.

A
  • Greater total cross sectional area (lots of arteries will have a greater collective area than a single aorta)
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19
Q

RECAP - Why is there a further reduction in blood velocity through the arterioles and capillaries?

A
  • Individually, each arteriole and capillary has a low cross sectional area.Collectively, total cross sectional area is high ∴ blood velocity is low
  • Cardiac output is transferred into the high number of arterioles and capillaries. The arterioles can also influence resistance to blood flow.
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20
Q

RECAP - Why is blood velocity in the venous system high?

A
  • Blood funnelled back into the venous system which has fewer vessels compared to capillaries
  • Lower total cross sectional area - blood returns to heart in a reasonable timeframe
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21
Q

What is the equation for velocity of blood flow?

A

Blood flow/cross-sectional area

22
Q

Describe laminar blood flow

A
  • Flow in regular concentric (arch) shapes
  • Zero velocity at the walls due to friction and highest at the centre.
  • Most red blood cells are found at the centre. This speeds up blood flow through narrow vessels
  • Usually occurs in arteries, veins etc.
23
Q

Describe turbulent blood flow

A
  • Blood flows in whirlpools and vortices due to increased pressure and velocity.
  • Has a high resistance to flow.
  • Occurs in aorta and vessels affected by atheroma
24
Q

Describe bolus blood flow

A
  • Red blood cells have a larger diameter compared to that of the capillaries and so move in a single file. Plasma columns found before and after each red blood cell
  • Has uniform velocity with very little internal friction and very low resistance to flow
  • Allows maximum access for gas and nutrient exchange.
25
Q

What does Reynold’s number determine?

A
  • Determines change from laminar to turbulent flow
26
Q

Refeering to Reynold’s number, when might blood flow transition from laminar to to turbulent blood flow?

A
  • Turbulent flow occurs when Reynold’s number exceeds a critical value (usually 2000)
  • Below this critical value flow will be laminar.
27
Q

What is the mathematical equation for Reynold’s number?

A

Reynolds number = (Density x Velocity x Diameter)/ Viscosity

In order to increase Reynolds number increase density, diameter and velocity and decrease viscosity

28
Q

What generates the pressure exerted by blood on vessel walls?

A

Left ventricular contraction

29
Q

Describe the relationship between distance from left ventricle and arterial pressure

A

As distance from left ventricle increases, arterial pressure will decrease

30
Q

What type of vessels are arterioles and which type of nervous system are they controlled by?

A

Arterioles are resistance vessels which are under sympathetic control

31
Q

What is systolic pressure?

A

Pressure when contracting and ejecting blood into circulation e.g used by left ventricle to eject oxygenated blood into systemic circulation

32
Q

What is diastolic pressure?

A

Pressure when relaxing

33
Q

What is pulse pressure?

A
  • Difference between diastolic and systolic pressure
  • This is the “pulse” we feel with our fingers.
34
Q

How is pulse pressure related to stroke volume and compliance?

A

Pulse pressure = Stroke volume/ Compliance
If compliance is low then pulse pressure is high. If stroke volume is high then pulse pressure is high

35
Q

What is compliance?

A

The ability of a vessel wall to stretch.

36
Q

Why do arteries generally have high compliances?

A

This is due to the thick layer of smooth muscle they have in the arterial wall

37
Q

What is the effect of a blood vessel having a high compliance?

A

Require a high pressure in order to increase their volume.

38
Q

What is mean blood pressure?

A

Average pressure between systolic and diastolic pressure

39
Q

What happens to the aorta and arteries during left ventricular systole?

A

Arteries and aorta expand
- This causes energy to be stored within the stretched elastin

40
Q

What happens to the aorta and arteries during left ventricular diastole?

A
  • Energy returns back to the blood as the walls of the aorta and arteries contract.
  • Sustains diastolic blood pressure and flow when the heart is relaxed
41
Q

Describe the changes in the arteries when going form rest to exercise.

A
  • Greater stretch of the arteries as more blood is ejected (stroke volume).
  • Causes less compliance and less recoil.
  • Pulse pressure also increases
42
Q

How is arterial pressure affected by age?

A
  • In older people their arteries become stiffer (atherosclerosis) causing a decrease in compliance
  • Large pulse pressure will be present throughout the arterial tree.
43
Q

How does arterial pressure change as we go down the arterial tree?

A
  • Pulse pressure becomes more noticeable as vessels become less compliant
  • Pulse is measured at the radial artery as it is quite far from the heart however cannot be detected in the arterioles as flow is more continuous
44
Q

What controls mean blood pressure?

A
  • Age (less compliance and atherosclerosis)
  • Disease (cardiovascular diseases)
  • Distance along arterial tree (less compliance further from the arterial tree)
  • Exercise (Stroke volume and Cardiac Output)
  • Emotions (Stress, anger, fear)
45
Q

What is the effect of vasoconstriction of the veins?

A
  • Increases volume of blood that is returning to the heart
  • Increase the stretch on the wall of the heart.
  • Increased force of contraction and greater stroke volume, thereby increasing cardiac output.
46
Q

Name one flaw of Darcy’s Law

A
  • Darcy’s law accounts for pressure determining flow, but in reality there are other factors involved.
  • There are times when flow can be against a small pressure gradient so the pressure difference between CVP and the heart could be almost zero, yet still get good filling of the heart
47
Q

During an auscultation, what sounds may represent turbulent blood flow?

A
  • Ventricular filling
  • Contraction of the aorta during ejection
  • Bruits - occur when blood flow through occluded blood vessels
48
Q

With reference to Reynold’s Number, describe the relationship between flow and pressure.

A
  • Initially linear with laminar flow
  • Above critical value, becomes turbulent - greater energy required to drive blood flow.
49
Q

Would anaemia cause turbulent or laminar blood flow?

A

Turbulent
- due to reducing blood viscocity

50
Q

Atherosclerosis contributes to turbulent blood flow. Suggest why.

A
  • Narrower blood vessels so diameter reduces
  • Cross-sectional area is lower
  • Causes an increase in velocity
51
Q

What is the formula for mean blood pressure?

A

Diastolic pressure + 1/3(pulse pressure)

SGUL - Physiology 1 (68 decks)

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