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Cardiorespiratory Biology > Haemodynamics > Flashcards

Haemodynamics Flashcards

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1
Q

blood flow is analogous to give comparison

A 
electrical current
V = IR 
v = Voltage 
I = current 
R = resistance
/_\P = QR
/_\ P = Pressure gradient
Q = flow
R = Resistance
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2
Q

Ohm’s law

A

V =IR
V =voltage
I = current
R = Resistance

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3
Q

Darcy’s law

A

perfusion or flow = pressure gradient / resistance

Q = /_\P/R

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4
Q

how can Darcy’s law be applied to the whole CVS system

A 
flow = pressure gradient / resistance
– CO = MAP ÷ TPR
– cardiac output (CO)
– mean arterial pressure (MAP)
– total peripheral resistance (TPR)
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5
Q

what do we mean by mean arterial pressure

A

the average pressure across the cardiac cycle

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6
Q

where is the pressure generated

A

in heart during systole

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7
Q

cardiac output determines

A

systolic pressure

increased CO = increased systolic pressure

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8
Q

pressure of aorta

A

~100mmHg

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9
Q

pressure of capillaries

A

~25mmHg

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10
Q

pressure of great veins

A

~2 mmHg

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11
Q

vascular resistance influenced by

A

viscosity - thicker =faster
length = shorter = faster
vessel radius = wider = faster

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12
Q

how is poiseuille’s law applied to resistance to flow

A

R = ηL / r^4

– η is viscosity, L is length and r is vessel radius

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13
Q

vessel radius on resistance

A

tiny change to radius can have big impact

inversely proportional to power of 4

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14
Q

site of most vascular resistance

A

arterioles

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15
Q

why are resistance greater in small arteries than large arteries

A

• Large elastic conductance arteries have limited capacity to vary diameter
– unlike small muscular arteries and arterioles
• Thus resistance is largely generated in these small arteries and arterioles

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16
Q

small changes in diameter of blood vessels lead to

A

big changes in flow
blood will go where resistance is less - control perfusion to allow blood to go to tissue where nutrients is most in demand

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17
Q

what is viscosity proportional

A

proportional to resistance

inversely proportional to flow

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18
Q

why is blood thicker than water

A

2.5 -3 times more viscous than water

plasma proteins and red blood cells

19
Q

haematocrit - HCT

A

the proportion of blood volume occupied by red cells

20
Q

haematocrit of women

A

37-47%

21
Q

haematocrit for men

A

40-54% - more viscous than women

22
Q

how will haematocrit affect viscosity

A

anaemia - lower HCT - less viscous

polycythaemia - higher HCT increase viscosity

23
Q

why slight decrease in haematocrit in capillaries and smaller vessels

A

Capillaries and smaller vessels (<300 μm) tend to have (slightly) lower
haematocrit due to axial accumulation
rbc cells in centre of flow - branches get more plasma than rbx

24
Q

do we excpet radius or viscosity to have a greater impact on resistance and therefore flow

A

– r
4 has much more effect on flow than 
– it is just slightly faster than it would expected

25
Q

blood flow is

A

laminar

26
Q

laminar speed

A

speed of blood slows as we move closer to vessel wall - silent smooth and continuous
highest velocity in the centre

27
Q

if blood flow is laminar what factor must be important

A

size

28
Q

how is flow changed in small arteries

A

Since small arteries have a large area to volume, most blood is near the wall and there is a large effect on flow
– here increased viscosity slows flow

29
Q

how is flow changed in larger arteries

A

In larger arteries, there are more layers and so increased velocities
– this diminishes the effect of viscosity

30
Q

consequence of speed

A

increased chance of turbulence

31
Q

where does non laminar flow tend to occur

A

in ascending aorta and around branch points - narrowed points where velocity increases

32
Q

basis of measuring turbulent bloodflow

A

he basis of Korotkoff sounds in measuring BP
– the basis of bruit in atheroma
– and also bronchial breathing

33
Q

transmural pressure

A

• The transmural pressure is the pressure that either distends or collapses blood vessels

34
Q

transmural pressure formula

A

pressure pushing in - pressure pushing out

35
Q

• If the pressure outside (Po) exceeds the pressure inside (Pi) what happens

A

• If the pressure outside (Po) exceeds the pressure inside (Pi) then the vessel will collapse

36
Q

what is transmural pressure related to

A

the wall tension and the radius

– The Law of LaPlace

37
Q

law of laplace transmural pressure

A

wall tension divided by radius

– PTM = T ÷ r or rearranged to T = PTM x r

38
Q

wall tension

A

how “thick” the vessel wall needs to be

39
Q

wall tension needed for vessels with small radius

A

less wall tension is required to balance

out the distending pressure

40
Q

wall tension needed for larger radius

A

more wall tension is required to

balance the distending pressure

41
Q

which vessels are more distensible veins or arteries

A

veins x 8

42
Q

compliance

A

the change in volume for a given change in pressure and
so relates to a vessels distensibility
– C = ΔV ÷ ΔP so can be rearranged to ΔV = C x ΔP

43
Q

what vessels are more compliant

A

veins x 20 more compliant than arteries

Cardiorespiratory Biology (25 decks)

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