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Biomedical Engineering > Heart > Flashcards

Heart Flashcards

1
Q

What is a soft Tissue?

A

proteins and polymeric materials. e.g. cartilage, tendons, ligaments and hair plant kingdom (bamboo, grass, trees).

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2
Q

What is a hard Tissue?

A

mineralised tissue; addition of ceramic phase to polymers e.g. shells, teeth and bone.

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3
Q

What is collagen?

A

Fibrous protein that imparts structure and rigidity to tissue. Most abundant protein in higher vertebrates.
Basic structural element for soft and hard tissues; provides mechanical strength and integrity.
Hallmark is a right-handed triple helix structure - composed of three polypeptide chains - each of which contains a repeating amino acid motif

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4
Q

What are fibrillar Collagens?

A

These proteins give rise to classic collagen fibrils (characterised by a repeating banding pattern, D-period, 64-67 nm). - Fibrillar collagens include: Type 1 (found in skin, tendon, bone, cornea, lung and vasculature)

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5
Q

What is elastin?

A

Fibrous elastic protein that imparts elasticity and resilience to tissue. Much more compliant than collagen (Young’s modulus ~ 1 MPa) Elastin is an ‘elastic protein’ (rubber-like protein) deform reversibly without loss of energy (high resilience), ability to deform to large strains with little force (hence elastic proteins have low stiffness). This combination of high resilience, large strains and low stiffness is the hallmark of rubber-like proteins such as elastin which function in the storage of elastic-strain energy.

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6
Q

Where is elastin found?

A

Found abundantly in large arteries, lung and skin

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7
Q

Do collagen fibres stretch?

A

Collagen fibres provide excellent energy storage capacity but do not stretch! Elastin exhibits reversible deformation with very high resilience.

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8
Q

What is the key function of elastin?

A

To provide low stiffness, high strain and efficient elastic-energy storage.

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9
Q

Where does elastin function?

A

Elastin functions alongside collagen in vertebrate connective tissues - Where soft, reversible elasticity is required (such as skin and cartilage) - Major component of arteries; its stretchiness allows arteries to smooth the pulsatile flow of blood from the heart, lowering peak blood pressure and the mechanical work of the heart and maintaining a steady blood flow.

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10
Q

What is the role of the circulatory system?

A

Delivers oxygen, nutrients and hormones throughout the body, Removes waste products from tissues, Provides a method for regulating temp and removing heat generated by internal organs

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11
Q

Whats the difference between the left and right side of the heart?

A

Right – heart pumps deoxygenated blood from the body through the pulmonary artery to the lungs.
Left – heart takes oxygenated blood from the lungs and pumps it to the body.
Each

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12
Q

What are the 2 types of blood vessels?

A

Arteries - carry blood from the heart.

Veins - deliver blood to the heart

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13
Q

What units is blood flow normally expressed in?

A

ml/min

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14
Q

Whats the overall blood flow in an adult?

A

5000ml/min

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15
Q

What is the equation for flow?

A

Q=VA where Q = flow, V = velocity, A = x=sec area

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16
Q

What is the branching network of arteries?

A

Aorta takes oxygenated blood
Arteries branch from Aorta to deliver blood to organs and body  Arteries divide into Arterioles  Arterioles deliver blood to capillary beds

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17
Q

How does the branching network relate to area?

A

Because the same volume of blood must flow through each segment of the circulation each minute, the velocity of blood flow is inversely proportional to vascular cross-sectional area. Under resting conditions, the velocity averages about 0.33m/s in the aorta but only 1/1000 as rapidly in the capillaries, about 0.003m/s

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18
Q

What is a bifurcating network?

A

Bc = 2 would be a bifurcating network where Bc is the branching configuration i.e. number of branches at each level

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19
Q

What is the mean diameter and length of each blood vessel in a network?

A

𝑑𝑖 = 𝑑𝑜𝐷𝑅 𝑖 𝑎𝑛𝑑 𝑙𝑖 = 𝑙𝑜𝐿𝑅 𝑖

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20
Q

What are typical values for Dr?

A

It varies between Dr = 0.600 (coronary circulation) and Dr = 0.616 (renal circulation)

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21
Q

What are the total number of generations for bronchial, pulmonary and kidney, heart and brain?

A

Total number of generations also consistent with 12 for bronchial circulation, 17 for pulmonary, and 13 each for kidney, heart and brain

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22
Q

Is the branching configuration constant?

A

Bc is not constant. Typically starts at 2 near parent vessel, then becomes 3 for a number of generations before becoming more complex  Simple power laws can be used for most approximations

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23
Q

What is Murray’s Law?

A

For a parent artery giving off j daughters, the diameters are related:
𝑑0^3 = 𝑑1^3 + 𝑑2^3 + 𝑑3^3 …+ 𝑑𝑗 3
Say we have 4 daughter branches in each level 𝑑𝑛 3 = 4𝑑𝑛+1 3 or 𝑑𝑛+1/𝑑𝑛
= ^3√( 1/ 4
)
3
= 0.63

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24
Q

What is the conservation of Energy (Bernoulli’s equation)?

A

𝑃1 +1/2𝜌𝜐1^2 = 𝑃2 +1/2𝜌𝜐2^2

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25
Q

What is Bernoulli’s equation for a change in elevation?

A

𝑃1 + 1 /2𝑟𝑣1^2 + 𝑟𝑔𝑦1 = 𝑃2 + 1/2𝑟𝑣2^2 + 𝑟𝑔𝑦2

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26
Q

What are the assumptions made when using Bernoulli?

A

Incompressible fluid, Negligible friction losses, Mechanical energy at any point is constant

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27
Q

What is an aortic aneurysm?

A

Abdominal aortic aneurysm involves a widening, stretching or ballooning of the aorta. As the aorta gets progressively larger over time there is increased chance of rupture – as xsec area increases, pressure increases

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28
Q

What is a transient ischemic attack?

A

Like a mini stroke occurs when a constriction in the subclavian artery causes the blood velocity to speed up.

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29
Q

What happens when arteries become constricted?

A

A person with constricted arteries will find that they may experience a temporary lack of blood to the brain as blood speeds up to get past the constriction, thereby reducing the pressure.

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30
Q

What is laminar flow?

A

When blood flows through a long smooth vessel it flows in straight lines, with each layer of blood remaining the same distance from the walls of the vessel throughout its length.When laminar flow occurs the different layers flow at different rates creating a parabolic profile. The parabolic profile arises because the fluid molecules touching the walls barely move because of adherence to the vessel wall. The next layer slips over these, the third layer slips over the second and so on.

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31
Q

What is turbulent flow?

A

At high flow rates flow can become turbulent. Turbulence characterised by highly irregular flow.This leads to a more uniform average velocity but greater viscous losses during flow. Reynolds found a characteristic velocity for each fluid depending on various parameters

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32
Q

What is Reynolds number?

A

Reynolds experiments on fluid flow in tubes found turbulence occurred above a critical velocity 𝑅𝑒=𝜌𝜈𝑙/𝜂

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33
Q

What is Reynolds number for turbulent flow?

A

Re-2𝜌𝑄/𝜋𝜂𝑅𝑎

where Ra is radius of aorta.

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34
Q

What is a heart murmur?

A

A heart murmur is an abnormal sound caused by turbulent blood flow. Can occur as a result of any various heart valve defects or type of congenital heart disease

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35
Q

How can a heart murmur be detected?

A

Abnormal sounds due to turbulent blood flow can be heard with a stethoscope.

36
Q

How does viscosity affect the resistance to flow?

A

Viscosity impedes the relative flow in adjacent layers and slows flow of the fluid

37
Q

What 3 factors determine the resistance to blood flow within a single vessel?

A

Vessel diameter (or radius), Vessel length, Viscosity of the blood.

38
Q

What is Poiseuille’s Law?

A

Poiseuille’s states that resistance to flow is a function of physical properties of vascular system. Newtonium fluid – η is constant. Constant flow rate and laminar flow (Re<2000); parabolic distribution of velocities form 0 at wall (no-slip principle) to a maximum at centre of lumen

𝑄 = Δ𝑃((𝜋𝑅^4)/ 8𝜂𝐿)

39
Q

Why is radius raised to 4th power?

A

Its importance in determining resistance is paramount. 20% increase = doubling in flow if all other variables constant. Coronary artery with a 2mm diam (e.g. a distal obtuse marginal) has 16x more resistance than a coronary with a 4mm diameter. Larger the tube or smaller the radius = greater resistance. Resistance affected more by radius than changes in length or viscosity.

40
Q

What does Poiseuille assume?

A

Newtonian fluid, laminar flow, no slip at vascular wall, steady flow, cylindrical shape, rigid wall.

41
Q

If radius of artery is half of what it should be, what factor does the pressure have to increase by to keep the same flow?

A

16

42
Q

What is arteriosclerosis?

A

General term for degenerative changes in arteries making them less elastic

43
Q

What is atherosclerosis?

A

Deposition of mineral (calcium) deposits (plaque) in blood vessels.

44
Q

Whats the difference between Poiseuille and Bernoulli?

A

Poiseuille’s equation can only be used to model flow for large vessels (i.e. arteries) where the vessels do not change much in diameter. In smaller vessels and capillaries, where the shear is low, blood must be treated as a nonNewtonian fluid and Poiseuille’s equation does not apply. For a constriction or dilation in the vessel, then Bernoulli’s equation can be used although there will be errors introduced by not accounting for blood viscosity.

45
Q

What is the purpose of blood pressure?

A

Required to transport blood through complex networks of arteries and veins/

46
Q

Why do pressure drops occur?

A

Pressure drop occurs because of viscosity effects. Pressure drop scales as 1/R^4 where R is tube radius

47
Q

How do arteries change in size as they become more distant from the heart?

A

They get smaller

48
Q

What is typically the highest pressure in the aorta?

A

typically 11 - 18kPa. Because the heart pumps blood continually into the aorta, the mean pressure in the aorta is high.

49
Q

What does the arterial pressure alternate between in a pumping heart?

A

Heart pumping is pulsatile, the arterial pressure alternates between a systolic pressure level of 120 mm Hg and a diastolid pressure level of 80 mm Hg.

50
Q

What happens to the mean pressure as the blood flows through the systemic circulation?

A

As the blood flows through the systemic circulation, its mean pressure falls progressively to about 0 mm Hg by the time it reaches then termination of the venae cava where it empties into the right atrium of the heart.

51
Q

What is the flow and area in capillaries?

A

Capillaries give slow flow and high surface area – favours exchange of material

52
Q

What does the heart put most energy into?

A

most energy from heart goes into pushing blood through capillaries.

53
Q

Why does obesity create problems for the heart?

A

Obesity creates large beds of capillaries in fatty tissues - making heart work harder to force blood around body. This requires higher blood pressure

54
Q

What is hypertension?

A

An increase in blood pressure, can happen for many reasons - Obese patients require capillary network in adipose tissue. Increase in total capillary area requires greater pressure from transport

55
Q

What are blood vessels?

A

Blood vessels are bioviscoelastic solids. They have a non-linear stress-strain relationship and hysteresis. Creep under constant stress, relax under constant strain.

56
Q

What are the 3 structural layers of blood vessels?

A

Surface of vessel - tunica intima; Thick elastic layer - tunica media; Outer acellular layer - tunica adventitia

57
Q

What are elastic arteries?

A

Largest diameter e.g. aorta; ability to stretch and hold additional volume when pressure increases; Thick tunica media; large amount of elastin.

58
Q

What are muscular arteries?

A

Intermediate-sized vessels; Tunica media largely composed of Smooth muscle; Can change diameter to influence flow through vasocontriction and vasodilation

59
Q

What are arterioles?

A

Diameter <0.5mm ; Muscular TM up to 5 layers thick; composed entirely of SM; Approx. 70 % pressure drop between heart and veins occurs in small arteries and arterioles.

60
Q

How does pressure change with size in arteries?

A

Thick walled main arteries and aorta withstand pressures of 10 – 16 kPa and high speed blood flows. As we depart from major arteries pressure variation decreases and max. pressure reduces to 9 – 11 kPa. Arteriole pressures are around 6.5 – 9 kPa with smallest capillaries operating at 1.5 – 4 kPa

61
Q

What is the composition of arteries?

A

Predominant elastic materials - collagen and elastin. Arterial wall divided into 3 concentric zones: tunica intima, media and adventitia. Distribution of collagen and elastin differs between central and peripheral arteries.

62
Q

What is the tunica media?

A

It forms major part of the vessel wall and determines vessel mechanical properties.

63
Q

As distance from the heart increases, arteries become…

A

stiffer

64
Q

What is the equation for finding stress in the artery wall?

A

< 𝜎𝜃 >=𝑃𝑎/𝑡 where a = radius of artery and t = wall thickness

65
Q

What happens to arteries as stress increases?

A

Arteries not linearly elastic, As stress increases, stiffness increases.A model for the non-linear behaviour - Thin coils represent “weak” elastin fibres at different lengths, Heavy coil represents “stiff” collagen fibres which are initially not under tension

66
Q

What do veins do?

A

Return low pressure blood from capillary beds or lungs to the heart. Rich in smooth muscle which responds to neural, humoural, pharmacological and mechanical stimuli.

67
Q

What’s the difference between veins and arteries w.r.t wall thickness?

A

Veins have much smaller wall thickness than arteries

68
Q

What are the mechanical properties of veins?

A

Vein walls can deform under action of external pressure.Collapse of veins is possible if there is a negative pressure difference.
Large veins – more cellular, Less ECM (low pressure blood), Structure relates to function – contrast aorta with vena cava.

69
Q

Why do veins have much thinner walls than arteries?

A

Veins are much thinner walled than arteries on account of the lower pressures.

70
Q

Why are valves necessary in some veins?

A

Valves are necessary in some veins (e.g.legs) to prevent pooling of blood

71
Q

What is the blood pressure of veins?

A

On the venous side the blood pressure starts at around 4kPa and falls close to 0

72
Q

What happens in veins as flow velocity increases?

A

On the venous side the blood pressure starts at around 4kPa and falls close to 0. Limiting flow velocity above which tube walls collapse restricting further flow

73
Q

What effect does muscle action have on veins?

A

Because veins are thin walled external muscle action can affect them. Pressure in vein in ankle when standing would be the hydrostatic pressure. As person walks we get changes in local pressure because of muscle action

74
Q

What are the three primary ways through which blood vessel tissue structure changes?

A

Ageing, Disease and change in mechanical load. Sometimes a combination of all 3.

75
Q

What are the effects of arterial stiffening?

A

Important implications for CV function in ageing. Loss of arterial wall elasticity = greater work for heart Alters ability of large arteries to cushion pressure and flow during systole and to release pressure and flow towards distal arteries during diastole.

76
Q

What happens to stress during hypertension?

A

Increased stress due to aortic pressure – changes in collagen and elastin content. Relationship between intra-aortic pressure (P) and aortic lumen area (AL)

77
Q

What are the consequences of high blood pressure?

A

Systolic blood pressure increased from 2kPa to 2.93 kPa within minutes; After 12 hours, significant thickening of the ML in the pulmonary artery; After 96 hours the adventitia has also experienced a significant increase in thickness.

78
Q

Is atherosclerosis due to ageing?

A

Disease which is distinct and separate from ‘normal’ ageing. Atherosclerosis is initially and predominantly intimal disease. Localised to sites in major arteries

79
Q

What is Pulse Wave Velocity?

A

Index of arterial stiffness. A simple method to assess arterial stiffness and distensibility; A long established and widely used technique; Non-invasive, accurate and reproducible.

80
Q

How does pulse wave velocity work?

A

L.V.E generates a pulse wave which will propagate along the arterial walls at a certain speed. Blood = compressible fluid, Artery = elastic conduit  Propagation along the arterial tree

81
Q

What is the process of ventricular contraction?

A
  1. Ventricle contracts.
  2. Semilunar valve opens
  3. Aorta and arteries expand and store pressure in elastic walls
82
Q

What is the process of ventricular relaxation?

A
  1. Isovolumetric ventricular relaxation
  2. semilunar valve shuts
  3. Elastic recoil of arteries sends blood forward into rest of circulatory system
83
Q

What are the principles of Pulse Wave Velocity?

A

The propagation velocity is determined by the elastic and geometric properties of the arterial wall and the characteristics of the arterial wall structure.
Higher velocity = higher stiffness, lower distensibility

84
Q

What is the most widespread index of arterial stiffness?

A

aortic PWV; the speed at which the elastic distortion of the blood vessel wall propagates in response to the pressure pulse from the beating heart.

85
Q

How is PWV determines?

A

Determined by recording the time (δt) taken. PWV is related to vascular wall stiffness through the Moens-Korteweg equation.

86
Q

What is the Moens-Korteweg equation?

A

𝑐 = √ [𝐸(𝑎)ℎ/2𝜌𝑟]

87
Q

What effect does ageing have on circulatory system?

A

Stiffening of arteries with age; ill-effects on cardiac metabolism and function; Progressive throughout life; Increase in left ventricular load;Responsible for deterioration in CV function in younger people e.g. competitive sport.
Aorta radius neared heart expands with time; Artery thickness also increases to reduce stress in artery wall

Biomedical Engineering (1 decks)

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