Haemodynamics

Question 1

What is haemodynamics?

Answer 1

physical laws governing pressure/flow relationships in blood vessels

Question 2

fluid mechanics principles can apply to the CVS, but what is different?

Answer 2

blood is not simple ‘Newtonian fluid’ - contains red and whtie blood cells, platelets, lipds
blood vessels are not uniform, straight, rigid tubes

Question 3

Equation for flow

Answer 3

flow = change in p / resistance

p = pressure gradient between arteries and veins created by pumping heart action

Question 4

General structure if blood vessel

Answer 4

adventitia
media (smooth muscle, elastin, collagen)
intima (endothelium)
lumen

Question 5

How is there active control over the blood vessels?

Answer 5

smooth muscle contracts and relaxes, expanding and narrowing the lumen

Question 6

What is normally found between the media and adventitia?

Answer 6

sympathetic nerves which innervate the smooth muscle

causes vasoconstriction

Question 7

How does internal diameter and wall thickness change between blood vessels?

Answer 7

aorta - arteries - arterioles - capillaries - venules - veins - vena cava

decreases to capillaries then increases to VC

Question 8

How does elasticity and smooth muscle of arteries differ?

Answer 8

elasticity decreases with size

smooth muscle in areries and arterioles more

Question 9

Which blood vessels have no smooth muscle and is not elastic?

Answer 9

capillaries and venules

Question 10

Compare the total cross sectional areas with all the blood vessels

Answer 10

aorta < arteries < arterioles < capillaries

capillaries > venules > veins

Question 11

What can be used to see CSA?

Answer 11

change in velocity of the blood

increased velocity = decreased CSA

Question 12

What are the determinants of flow?

Darcy’s

Answer 12

Flow – directly related to the pressure difference (Pi-Po)

Flow – inversely related to the resistance (R)

Question 13

What are the determinants of flow?

Poiseuille’s

Answer 13

Flow – directly related to pressure difference (Pi-Po)
Flow – inversely related to length of tube (l)
Flow – inversely related to viscosity of fluid ()
Flow – directly related to radius of tube (r)4

Question 14

Key point for flow being directly related to pressure difference

Answer 14

greater the pressure gradient, greater the flow

Question 15

Key point for flow being inversely related to length of tube

Answer 15

longer the vessel, lower the flow

Question 16

Key point for flow being inversely related to the viscosity

Answer 16

increased viscosity, lower flow

Question 17

Key point for flow being directly related to the radius of the tube

Answer 17

greater radius of vessel, greater flow

Question 18

In real body, what is resistance (flow) actually determined by?

Answer 18

radius of the blood vessels

and pumping of the heart

Question 19

What is the exact relationship between relative radius and relative flow?

Answer 19

F ∝ r^4

slight increase in radius means large increase in flow

Question 20

Which vessels have the greatest capacity to change radius?

Answer 20

small arteries and arterioles

‘resistance vessels’

Question 21

Which vessels have the largest drop in pressure? why? and why is this important?

Answer 21

small arteries and arterioles
increased resistance due to change in radius
to decrease pressure before entering capillaries

Question 22

Equation for total peripheral resistance

Answer 22

arterial - venous P / cardiac output

Question 23

What also occurs in blood when flow changes?

Answer 23

smoothing of pulsatile blood to steady

Question 24

Equation for resistance

not necessary to remember

Answer 24

pressure difference / flow

Question 25

Why will individual blood flows be less than the total flow?

Answer 25

cardiac output is distributed to vascular beds (usually arranged in parallel)

Question 26

How is total peripheral resistance affected by parallel vascular beds?

Answer 26

less than individual resistance

Question 27

What is laminar blood flow?

Answer 27

velocity is max in the centre

straight flow

Question 28

What is turbulent flow?

Answer 28

lack of laminar movement

need higher dirving pressure to achieve same flow

Question 29

Why does turbulent flow occur?

Answer 29

when there is branches in the blood vessels

atherosclerosis - artificially narrows the vessels

Question 30

How do the vessels make blood flow as laminar as possible?

Answer 30

Vessels are not rigid tubes
Elasticity conferred by elastin + collagen
Elastic conduits (arteries) and high resistance arterioles have a smoothing effect on blood flow

Question 31

What is compliance in relation to blood vessels?

Answer 31

change in volume for a given change in pressure

Question 32

Arterial role in relation to compliance

Answer 32

provides filtering and smoothing

Question 33

Venous role in relation to compliance

Answer 33

provides capacity for storage

Question 34

If a blood vessel is compliant, what does this mean?

Answer 34

it is less distensible

Question 35

What is venous return affected by?

Answer 35

venomotor tone (constriction)
venous valve competence
skeletal muscle pump - muscle contraction in legs
respiration - increased inspiration, decreases intra-thoracic pressure, increases intra-abdominal pressure, provides pressure gradient