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BMS10 > Intro to CVS & Physics of Blood Flow > Flashcards

Intro to CVS & Physics of Blood Flow Flashcards

1
Q

Give two features of the circulatory system of the body

A

Closed

Double pump

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2
Q

How would you describe the resistance and pressure in the pulmonary circulation generally?

A

Low

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3
Q

How would you describe the resistance and pressure in the systemic circulation generally?

A

High

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4
Q

How is the pulmonary circulation arranged?

A

In series with systemic

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5
Q

How is the systemic circulation arranged?

A

Largely in parallel

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6
Q

What is the mean arterial pressure in the pulmonary circulation?

A

16mmHg

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7
Q

What is the mean arterial pressure in the systemic circulation?

A

92mmHg

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8
Q

Describe the changes in pressures in the systemic circulation

A

Very high in left ventricle

High in large arteries

Main decrease occurs in arteries and arterioles

Relatively lower decrease through capillaries

Decreases in venules

Remains low in veins

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9
Q

How do the pressure changes in the pulmonary circulation compare to those of the systemic circulation?

A

Similar trend but at much lower pressures

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10
Q

What is cardiac output?

A

Volume of blood ejected from left ventricle per minute

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11
Q

What is the cardiac output of the average person?

A

~5L/min

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12
Q

How can you calculate cardiac output?

A

Stroke volume x heart rate

Mean arterial pressure / total peripheral resistance

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13
Q

What is the stroke volume of the average person?

A

70-80ml/beat

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14
Q

What is the heart rate of the average person?

A

60-75 bpm

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15
Q

What is the ejection fraction?

A

Amount of blood ejected compared to what remains (%)

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16
Q

What is the ejection fraction used for?

A

Evidence of heart failure (<40%)

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17
Q

What is the ejection fraction of the average healthy person?

A

60-70%

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18
Q

How do you calculate the ejection fraction?

A

Stroke volume / end diastolic volume

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19
Q

What is TPR?

A

Total peripheral resistance

Resistance to flow mostly due to small arteries and arterioles

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20
Q

Which side of the heart is affected by TPR?

A

Left

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21
Q

What is the informal term used to describe TPR?

A

Afterload

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22
Q

How can you calculate mean arterial blood pressure?

A

Diastolic pressure + pulse pressure/3

CO x TPR

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23
Q

How do you calculate pulse pressure?

A

Systolic pressure - diastolic pressure

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24
Q

What is systolic pressure?

A

The maximum pressure reached in the heart

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25
Q

What is diastolic pressure?

A

The minimum pressure reached in the heart

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26
Q

For how long is the heart in systole?

A

1/3 of the time

27
Q

What is venous return?

A

Blood flow into the heart

28
Q

What is the venous return of the average person?

A

~5L/min

29
Q

What determines the filling of the heart with blood?

A

Central venous pressure/preload

30
Q

How do you calculate flow generally?

A

Pressure / resistance

31
Q

What is normal blood pressure?

A

120/80mmHg

32
Q

What is systole?

A

High pressure ejection of blood into large conduit arteries (lots of smooth muscle and elastin)

33
Q

How many layers of smooth muscle are there in the large conduit arteries?

A

60-100

34
Q

What happens to the large conduit arteries during systole and diastole?

A

Systole = stretch to store energy

Diastole = no outward flow so stored energy used to maintain flow (recoil)

35
Q

At what level must blood pressure always be measured?

A

At heart level

36
Q

What is Darcy’s law?

A

Flow = (P1 - P2) / R = pressure difference / resistance

37
Q

What is Poiseuille’s law?

A

R = 8VL / πr^4

38
Q

What equation do you get when you combine Darcy’s and Poiseuille’s laws?

A

Flow = (P1 -P2).πr^4 / 8VL

39
Q

What is the most important factor in determining resistance?

A

Radius of vessel/tube

40
Q

How is the resistance to flow affected by a larger length?

A

Increased

41
Q

How is the resistance to flow affected by a higher fluid viscosity?

A

Increased

42
Q

How is the resistance to flow affected by vasoconstriction?

A

Increased

43
Q

What are the assumptions made when using Poiseuille’s law?

A

Incompressible fluid

Newtonian fluid

Laminar flow

44
Q

How much thicker is blood than water?

A

3-4 times

45
Q

How does an increase in red cell mass affect plasma viscosity?

A

Increased

46
Q

How does anaemia affect plasma viscosity?

A

Decreased

47
Q

Where is the fastest flow in a tube/vessel and why?

A

Centre

Concentric layers of force due to viscous drag at sides of tube

48
Q

What is axial streaming?

A

Cells aligning in fastest moving fluid

49
Q

What is the Fahraeus-Lindqvist effect?

A

Describes how blood viscosity changes with vessel diameter (less blood cells in capillaries = lower viscosity)

50
Q

What causes turbulent flow?

A

High velocity flow, sharp edges and branch points

Disrupt laminar flow

51
Q

What causes heart murmurs?

A

Turbulent flow

High velocity blood flow due to stenosis/narrowed heart valves

52
Q

What is Reynold’s number for laminar flow?

A

<2300

53
Q

What is Reynold’s number for turbulent flow?

A

> 4000

54
Q

How does flow change as pressure increases in a rigid tube?

A

Flow increases proportionately

55
Q

How does flow change as pressure increases in a distensible tube?

A

Flow increases proportionately then exponentially as tube dilates

56
Q

How does flow change as pressure increases in a distensible tube with myogenic tone?

A

In response to pressure increase, smooth muscle contracts to limit flow

57
Q

Why is high velocity flow not desirable in blood vessels?

A

Causes damage to walls

58
Q

How do you calculate the total resistance in a series circuit?

A

Add resistances

59
Q

How do you calculate the total resistance in a parallel circuit?

A

Add conductances to get reciprocal of total resistance

60
Q

How are conductance and resistance related?

A

Conductance is the reciprocal of resistance

61
Q

Is total resistance higher in a circuit in series or parallel?

A

Series

62
Q

What is the advantage of having vascular beds arranged in parallel?

A

Resistance in one bed can be changed without greatly affecting net resistance or the resistances of other beds

63
Q

If blood pressure is constant, what controls flow through a tissue?

A

The tissue’s own resistance (ie. constriction/dilation of its own vessels)

BMS10 (13 decks)

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