Arteries, arterioles and veins Flashcards
What is haemodynamics?
relationship between blood flow, blood pressure and
resistance to flow
What is work?
Expend energy to produce
cardiac contraction which creates
Isovolumetric contraction
and ejection
What is pressure?
Generated to drive
bulk/convection transport
What is compliance?
Large artery stretch
Where is resistance generated?
Arterioles
Where is blood flow slowed down?
blood is slowed down in capillaries
What are the three patterns of blood flow?
- Laminar
- Turbulent
- Bolus
Where is laminar flow mostly found?
Most arteries, arterioles, venules,
veins
How can laminar flow be described and what is the behaviour like for RBC transport?
Concentric shells
Zero velocity at walls
(molecular interactions
between blood and wall)
Maximum velocity at centre
Move RBCs towards centre
Speeds up blood flow
through narrow vessels
Where is turbulent blood flow found?
Ventricles (mixing), aorta (peak flow),
Atheroma (bruits)
How can turbulent blood flow be described and what is this due to?
Blood does not flow linearly and smoothly
in adjacent layers (whirlpools, eddies,
vortices)
Due to changes in
velocity
Where is bolus flow found?
Capillaries
How would bolus blood flow be described?
RBCs have larger diameter than diameter
of capillaries – single file
Plasma columns are trapped between RBC
Uniform velocity
Little internal friction - very low resistance
What is the equation for blood flow?
Blood flow = Arterial blood pressure/Total peripheral resistance
What is pressure exerted by blood on vessels generated by?
Pressure exerted by blood on vessel walls
Ultimately generated by
left ventricular ejection
What happens to arterial pressure in systemic circulation?
Arterial pressure falls in systemic circulation
with distance from left ventricle
and effect of different blood vessels
What helps to propel blood into circulation during diastole?
Recoil of elastic fibers of the aorta and large arteries helps to propel the blood into the circulation during diastole
What happens during LV ejection in terms of arterial blood pressure?
60-80% of stroke volume is stored
in aorta and arteries as these
structures expand
Energy stored in stretched elastin
What happens during LV diastole to arterial blood pressure?
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
What is pulse pressure?
Pulse pressure is what the finger senses, e.g., at the wrist (radial artery)
What does pulse pressure tell us about?
Pulse Pressure tells you about STROKE VOLUME and Large ARTERY COMPLIANCE (stretchiness)
What is the equation for pulse pressure?
Pulse pressure = stroke volume / compliance
What does a weak pulse mean in relation to stroke volume?
Reduce stroke volume
Why does compliance decrease in the elderly?
Increase in age – stiffer arteries (arteriosclerosis) - decreased compliance
Increased systolic blood pressure
What would happen to an elderly patient, with decreased compliance, if they were to exercise?
Very large increase in systolic pressure
Increase in afterload
Heart functions poorly
What is the equation for blood flow?
Blood flow(Cardiac output) = Arterial blood pressure / Total peripheral resistance
What is the equation for arterial blood pressure?
Arterial Blood Pressure = CO x TPR
What 2 things does total peripheral resistance control?
Blood Flow and Blood Pressure
What happens if you have excessive drop in TPR (excessive vasodilation)?
Excessive dilation will reduce blood pressure upstream to an extent
that there will be insufficient pressure drive for blood flow
Poor blood flow to end organs, organ/tissue damage
What happens if you have excessive increase in TPR (excessive vasoconstriction)?
Excessive constriction leads to increase in blood pressure upstream and a
reduction in blood flow downstream
End organ damage
What does poiseuille’s law describe?
Poiseuille’s Law describes parameters that govern TPR
What is blood flow proportional to in terms of radius?
Blood Flow is proportional to Blood vessel radius to the power of 4 (r4)
-If you increase radius, you increase blood flow
What is blood flow proportional to in terms of visocisty?
Blood flow is proportional to 1 / viscosity
-If you increase viscosity, you decrease blood flow
What is TPR controlled by?
-Radius^4
-Pressure difference across vessels – P1-P2
-Length L
What is arteriole radius tightly controlled by?
Arteriole radius is tightly controlled by
sympathetic nerves
What vessels have the largest pressure drop?
Arterioles have largest pressure drop of 40-50 mmHg amongst vessels
What is viscosity?
Viscosity is a measure of internal friction
opposing the separation of the lamina
What does blood viscosity depend on?
- Haematocrit
- Velocity of blood
What clinical implications does high haematocrit have on viscosity?
e.g., Polycythaemia - Increased TPR and BP, Decreased BF
What clinical implications does low haematocrit have on viscosity?
e.g., Anaemia - TPR and BP (with HR
due to baroreflex compensation)
What clinical implications does velocity of blood have on viscosity?
Increased viscosity in slow venous flow
in immobile legs
Increased risk of DVT
Where is 60% of blood volume at rest found in?
60% of blood volume at rest is in
systemic veins and venules
What do veins and venules function as?
Functions as blood reservoir
How are veins innervated?
Innervated by sympathetic nerves which cause venoconstriction
What happens when there’s increased venoconstriction?
Contraction of vessels – Expels blood into central veins
– Increases venous return/CVP/end-diastolic volume
– Increases stroke volume (Starling’s law)
What is the equation for benous return?
Venous return = Venous Pressure – Pressure right atrium / Venous resistance
How does the thoracic pump assist with blood returning to the heart?
Inhalation - thoracic cavity expands leading to increase in abdominal pressure, forcing
blood upward towards heart, increase right ventricular SV
Blood flows faster with inhalation
What is retrograde flow in veins prevented by?
Retrograde flow is prevented by venous valves
What does the skeletal muscle pump reduce?
Reduce high local venous pressures when in the upright position
Reduces swelling of feet and ankles – lower venous pressures, lower capillary
pressure, less filtration
