Arteries Flashcards
What is haemodynamics?
relationship between blood flow, blood pressure and resistance to flow
key factors in haemodynamics
where is compliance?
where is resistance?
where is velocity reduced?
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
Cvs is a closed system
what does this mean for the whole system?
what happens if you reduce blood flow to one area?
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
where is the majority of the blood?
importance of this?
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
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?
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
blood flow, perfusion and velocity of blood flow
describe all of them and their units
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)
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?
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
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?
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
Turbulent Blood Flow
where? (3)
how does blood flow? why?
explain turbulent flow in an artheroma?
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
Bolus Blood flow
describe this in relation to rbc and capillaries
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
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?
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
when does turbulence occur in relation to reynold’s number?
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
Arterial blood pressure - general aspects
where is pressure exerted?
where is pressure generated?
highest and lowest values?
what happens to arterial pressure with distance?
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
Factors that affect arterial blood pressure (4)
Cardiac output – (Starling’s/Laplaces’s laws, Contractility, Heart rate)
Properties of arteries – aorta
Peripheral resistance – Arterioles
Blood viscosity – Haemocrit
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?
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
Why store blood?
significance of the recoil action?
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
what is pulse pressure?
what does it tell you?
equation for pulse pressure?
what happens to pulse pressure during exercise and why?
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)
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?
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)
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?
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
How does pulse pressure affect afterload
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
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?
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
How does decreased arterial compliance affect the curve?
how does Sv affect the differenr pressures?
Decreased compliance (steeper curve) = Stroke volume now increases systolic and pulse pressure disproportionally
Why is decreased arterial compliance important with the elderly?
name the condition
why it happens?
efect of this on systole and diastole? why?
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
Mean blood pressure calculation
eqaution? why this?
how to calculate it? ( 2 ways)
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
what controls mean blood pressure?
6 different things
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
