Arteries

Question 1

What is haemodynamics?

Answer 1

relationship between blood flow, blood pressure and resistance to flow

Question 2

key factors in haemodynamics

where is compliance?
where is resistance?
where is velocity reduced?

Answer 2

Force : Cardiac contraction

Work : Isovolumetric contraction / ejection

Pressure : Difference across circulation

Compliance : Arterial stretch

Resistance : Arterioles

Flow : The vital parameter

Velocity : slowing down blood flow in capillaries

Question 3

Cvs is a closed system

what does this mean for the whole system?
what happens if you reduce blood flow to one area?

Answer 3

What happens in one part of CVS has a major impact on other parts

Reduce blood flow to one area: Increases pressure above and may alter flow to other areas

Question 4

where is the majority of the blood?

importance of this?

Answer 4

Majority of blood in the venous system - low pressure reservoir system -

This reservoir of venous blood can be used to increase cardiac output -> Starling’s law

Question 5

what is darcy’s law and how does it relate to the body?

what is the equation?

how does this relate to the blood pressure equation?

importance of this?

Answer 5

Darcy’s law of flow states :
Q = P1 – P2/ R 
Q  = Flow  
P1-P2 = Pressure difference
R = Resistance to flow

Blood Flow (Cardiac output, CO) = Pa – CVP/ tpr

HENCE

Blood Pressure (Pa) = Blood flow (CO) x TPR

Vascular Resistance controls Blood Flow and Blood Pressure

Question 6

blood flow, perfusion and velocity of blood flow

describe all of them and their units

Answer 6

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

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

Velocity of blood flow
Blood flow divided by the cross-sectional area through which the blood flows (cm/s)

Question 7

Blood flow: Relationship with velocity

what is velocity as an eqaution?
how does flow relate to velocity and area?

what happens to velocity as vol stays the same and vessels begin to branch out?

Answer 7

Velocity = Volume flow / area HENCE
Volume flow = velocity x area
actual volume doesn’t change, only velocity and area

As total volume flow (ml/min) stays the same
Velocity of blood flow in aorta is high
Branching of arteries slows velocity
Greater the cross-sectional area, slower the blood flow
Slowest in capillaries
Velocity increases with veins coming together

Question 8

Laminar blood flow

where/ which vessels?

where is there 0 velocity and max velocity? why?

where do rbcs move and what happens at narrow vessels?

Answer 8

Most arteries, arterioles, venules, veins

Concentric shells
Zero velocity at walls (molecular interactions between blood and wall)
Maximum velocity at centre as friction at walls and less frcition at centre hence flows in the centre

Move RBCs towards centre
Speeds up blood flow through narrow vessels

Question 9

Turbulent Blood Flow

where? (3)
how does blood flow? why?

explain turbulent flow in an artheroma?

Answer 9

Ventricles (mixing), aorta (peak flow), Atheroma (bruits)

Blood does not flow linearly and smoothly in adjacent layers (whirlpools, eddies, vortices)
Due to changes in velocity

Reduce area of blood going through vessel therfore turbulent blood flow which could mean poor blood flow -> artheroma

Question 10

Bolus Blood flow

describe this in relation to rbc and capillaries

Answer 10

Capillaries
RBCs have larger diameter than diameter of capillaries – single file
Plasma columns are trapped between RBC creates an
Uniform velocity
Little internal friction - very low resistance

Question 11

blood flow - reynold’s number

what does it describe/determine?
what happens to Re initially and why? what does blood flow depend on in this case?

Answer 11

Describes what determines change from laminar to turbulent flow

initially R is unchanged as the diameter is the same therefore blood flow depends on pressure difference as the pressure increases so does blood flow

Question 12

when does turbulence occur in relation to reynold’s number?

Answer 12

Re = 2000 is Deviation from Darcy’s law
Turbulence occurs when Reynold’s number exceeds a critical value (> 2000)
e.g. bruits, ejection murmur – increased blood velocity

Question 13

Arterial blood pressure - general aspects

where is pressure exerted?
where is pressure generated?
highest and lowest values?
what happens to arterial pressure with distance?

Answer 13

Pressure exerted by blood on vessel walls

Pressure generated by left ventricular contraction

Highest in aorta, 120 mm Hg during systole, 80 mmHg during diastole

Arterial pressure falls steadily in systemic circulation with distance from left ventricle

Question 14

Factors that affect arterial blood pressure (4)

Answer 14

Cardiac output – (Starling’s/Laplaces’s laws, Contractility, Heart rate)

Properties of arteries – aorta

Peripheral resistance – Arterioles

Blood viscosity – Haemocrit

Question 15

arterial blood pressure - role of aorta

what specific to aorta helps bp?
what does it do during LV ejection?
what happens during LV diastole?

significances of this?

Answer 15

Recoil of elastic fibers of the aorta and large arteries
helps to propel the blood into the circulation

During LV ejection
60-80% of stroke volume is stored in aorta and arteries as these structures expand
Energy stored in stretched elastin

During LV diastole
Energy is returned to the blood as the walls of the aorta and arteries contract
This sustains diastolic blood pressure and blood flow when heart is relaxed

Question 16

Why store blood?

significance of the recoil action?

Answer 16

majority time in cardiac cycle spent in diastole when heart isnt ejecting therefore need to provide blood during this period as there will be low pressure when we don’t eject blood into aorta and arteries

Therefore, we have the recoil action which acts as a propulsion mechanism of blood through circulation towards end organs

Hence can continously produce a BP and drive for blood flow

Question 17

what is pulse pressure?

what does it tell you?

equation for pulse pressure?
what happens to pulse pressure during exercise and why?

Answer 17

It is what the finger senses, e.g. at the wrist (radial artery) and Tells you about stroke volume and arterial compliance (stretchiness)

Pulse pressure = stroke volume / compliance
during exercise more pulse pressure as more SV but same compliance
Pulse pressure = Systolic pressure - Diastolic pressure
= 40 mm Hg
(from 80 to 120 to 80 to 120 is due to SV from heart)

Question 18

how pulse pressure changes with cardiac cycle? hence systole and diastole?

6 stages?
why is there a systolic decline? what does it do?
what causes the notch/slight increase in pressure?
what causes run-off pressure for diastole?

Answer 18

1 – Ejection, 2 – Peak Systolic

3 – Systolic decline (aorta compliance) hence stretching of the arteries and holding onto blood flow causes decline in pressure and increased volume under pressure

4 – Incisura/dicrotic notch (closure of aortic valve), causes a little increase in pressure

5 – Diastolic run off, 6 – Peak Diastolic -> closed system in diastole which leads to a run-off pressure (no ejection)

Question 19

arterial blood pressure - pulse pressure and SV. comparing rest vs exercise

what does a greater SV do to arteries?
what happens to compliance during exercise and why?

what does the sigmoid curve mean?

Answer 19

Greater SV - Greater stretch of arteries - Less compliant -> Relatively greater systolic pressure

As we get more blood in elastic arteries, we see an increase in arterial pressure because if we stretch and stretch large vessels more + more, arteries like elastic bands are only compliant/elastic to an extent therefore they can’t stretch as much which means the pressure of blood within area of blood vessel will increase.

As you increase SV during exercise, during curve being sigmoid/not proportionate, there is a bigger pulse pressure whne you increase SV as you push vessels beyound how compliant they are

Question 20

How does pulse pressure affect afterload

Answer 20

increase pulse pressure will increase afterload which means heart won’t be functioning as well as it should be

could be during max exercise hence max that heart can function

Question 21

arterial blood pressure - pulse pressure and decreased compliance

example? effect of this? effect on heart?

how do you measure compliance? how does this relate to the example?

Answer 21

Decreased compliance, e.g. Elderly – same change in volume, now greater pressure (small increase leads to great change and increases the load on the heart)

Compliance of vessel = Change in volume /
Change in pressure
therefore reduced compliance means less volume held and more pressure increase

Question 22

How does decreased arterial compliance affect the curve?

how does Sv affect the differenr pressures?

Answer 22

Decreased compliance (steeper curve) = Stroke volume now increases systolic and pulse pressure disproportionally

Question 23

Why is decreased arterial compliance important with the elderly?

name the condition
why it happens?
efect of this on systole and diastole? why?

Answer 23

Increase in age – stiffer arteries (arteriosclerosis) - decreased compliance

also, issue at rest as aorta and arteries lose compliance due to increase fibrosis hence they lose their elasticity. This can lead to increased systolic bp and decreased diastolic bp due to holding onto less blood volume hence less recoil action and low pressure will lead to poor blood flow to end organs

Question 24

Mean blood pressure calculation

eqaution? why this?
how to calculate it? ( 2 ways)

Answer 24

MAP = 2/3 DBP + 1/3 SBP as time spent in diastole is twice as long
Mean BP = area under curve – too complicated
Mean BP = diastolic pressure + 1/3 [pulse pressure]
therefore mean is around 93.3

Question 25

what controls mean blood pressure?

6 different things

Answer 25

Age 
Disease
Distance along arterial tree
Blood volume – SV, CO
Exercise – SV, CO 
Emotion – Stress, anger, fear, apprehension, pain due to sympathetic response so fight or flight increase BP
during Sleep - decrease BP, 80/50 mmHg