CVPR Week 2: CV system and Hemodynamics Flashcards
Objectives
Components of the Cardiovascular system
The circuitry of the cardiovascular system
Arteries carry…
blood from the heart to the capillaries
Veins carry…
blood from the capillaries back to the heart
Structural relationships of blood vessels
Large arteries properties
- conduit vessels: conduct blood under high pressure to tissues
- Highly elastic
Elastic recoil of arterial walls
Compliance = Δ volume
Δ pressure
Maintains relatively constant flow during the entire cardiac cycle
the arteries expand during systole and then recoil during diastole acting as a secondary pump to keep flow constant during diastole
Compliance equation
Compliance = Δ volume
Δ pressure
Elastic recoil of arterial walls: Rigid arteries
compliance would be 0
Compliant vs rigid flow: why is constant flow through the capillaries important?
rigid vs compliant arteries
constant flow is important because
- to have constant perfusion to the tissues and nutrient/waste exchange
Small arteries and arterioles properties
- large proportion of vascular smooth muscle
- highly innervated (almost exclusively by the sympathetics)
- “Resistance vessels”
Small arteries and arterioles AKA
Resistance vessels because they can provide the most resistance of any other segment
Properties of veins
- conduct blood under low pressure back to the heart
- thin walled
- can contract because they have a little smooth muscle
- sometimes they are innervated as well
- “capacitance vessels” because they are a volume reservoir
Veins AKA
Capacitance vessels
Blood volume distribution
~2/3 in the veins
16% in arteries
How veins regulate blood volume distribution
- veins constrict
- can drive a venous return
- usually doesn’t return to capillaries because of a small pressure gradient
- ↑ Venous Return in response to sympathetic nerve activity to veins to constrict
- An ↑ venous return results in ↑ cardiac output and ↑ Mean arterial blood pressure
An ↑ venous return results in
↑ cardiac output and ↑ Mean arterial blood pressure
pressure characteristics of the systemic circulation
- The systemic mean arterial pressure is about 100 mmHg for just about every animal
- The pulmonary mean arterial pressure is about 15 mmHg
The mean pulmonary arterial pressure is?
About 15 mmHg
The mean systemic arterial pressure is
about 100 mmHg for just about every animal
pulmonary pressure gradient
15 - 5 = 10 mmHg
Systemic pressure gradient
100 - 2 = 98 mmHg
Pulse Pressure equation
systolic - diastolic = pulse pressure
Why is there a reduction in pulsatility from the arteries to the capillaries and beyond?
- Hydraulic filtering reduces pulse pressure gradients the farther out in the systemic circulation
- this is important because the capillaries are not designed for high pressure
A scenario where pulse pressure might be elevated
↓ compliance would result in ↑ pulse pressure maybe from arteriosclerosis or atherosclerosis
or
vasoconstriction increasing stroke volume from sympathetic stimulation
Atherosclerosis is a form of
Arteriosclerosis
Way to estimate MABP from an aphasic arterial pressure waveform
~MABP = Diastolic + 1/3(pulse pressure)
Largest pressure drop in the systemic circulation
comes in the arterioles or resistance arteries because they provide the highest resistance to flow across the systemic circulation
increase vasoconstriction causes
increased arterial pressure and reduced pressure thereafter like the hose kink
relationship between velocity of flow and cross-sectional area
- inverse relationship
- rivers wide slow flow
- rivers narrow fast flow
Velocity of flow equation
velocity = flow / area
Summary of arteries, arterioles, veins, pulse pressure changes, velocity and blood-tissue exchange
Determinants of vascular resistance
4 listed
MABP equation
TPR x CO = MABP
TPR AKA
Total peripheral resistance
Vascular resistance equation
Ways to get a change in pressure
increase in resistance or an increase in flow
Poiseuille’s Law
a halving of the radius results in a 16-time increase to resistance because R^4
very small changes in radius can have a big impact on resistance
Poiseuille’s Law
- a halving of the radius results in a 16-time increase to resistance because of r^4
- very small changes in radius can have a big impact on resistance
Vasoconstriction effects on vascular resistance
decrease in radius leads to increased resistance
Vascular wall thickening effect on resistance
- decrease in radius
- increase in resistance
- i.e. atherosclerosis, hypertrophy, hyperplasia of vascular smooth muscle, hypertension, pulmonary hypertension, inflammation of vessels, some forms of pulmonary hypertension can get hyperplasia of endothelial cells (plexa formations)
Causes of increase of blood viscosity
- dehydration (higher concentration of RBCs and solutes)
- polycythemia (tumor or high altitude)
Polycythemia increases?
Vascular resistance
Polycythemia negatives
more likely to clot and form microemboli which can form microthrombi
Resistance in series
Series and parallel resistances
How to calculate parallel resistance and its effects
resistance in parallel add in reciprocals so the more parallel resistances the lower the resistance
resistance to flow in the systemic system
- resistance to flow in the capillaries is lower than in the arterioles
- is counter-intuitive because an arteriole has a larger radius than a capillary and according to Poiseuille’s law
- how you have to look overall resistance and because of the parallel resistances in the capillaries the resistance is lower
The majority of vascular resistances are in?
Parallel with each other
The benefits of parallel resistances in the vasculature
- allows for greater flow with a smaller pressure gradient
- flow through each vascular bed can be differentially regulated by adjusting local resistance
- if the vessels were all in series than the pressure would be very high
Laminar vs turbulent flow
- Laminar flow has the highest velocity in the center and slower on the edges because of vessel wall friction
- turbulent blood flow increases resistance
*
Turbulent flow normally occurs where?
where vessels bifurcate
Turbulent flow can be predicted by?
Reynolds Number
A high Reynolds number predicts?
Turbulent flow
What is polycythemia???
Turbulent flow increases when?
3 listed
- Vessel diameter is large (such as in aorta)
- Blood velocity is high (exercise, cardiac valve stenosis, partial occlusion)
- Blood viscosity is very low (severe anemia)
The sound caused by turbulent blood flow in the heart?
Heart murmur
The sound caused by turbulent blood flow in a vessel?
Bruit
Flow equations
Flow in the context of blood is
Cardiac output
Cardiac output equation
Heart rate definition
beats/unit time (beats/min)
Stroke volume definition
volume of blood ejected per beat (mL)
How are vascular resistance and flow regulated in the body?
extrinsic (outside the vasculature) and intrinsic (inside the vasculature) regulatory mechanisms
Summary
The elasticity of large arteries allows for?
constant blood flow and pressure across the capillaries
The site of greatest vascular resistance
arterioles
What innervates the arterioles?
The SNS
What part of the vascular system serves as a reservoir and mediate blood distribution?
The veins
Are the veins innervated?
yes, by the SNS
What can affect the pulse pressure
decrease in compliance or an increase in stroke volume
How is nutrient/waste exchange maximized at the capillaries?
- High cross-sectional area
- low blood velocity
- thin-walled capillaries
Pressure equation
P = Q x R
Causes of decrease of blood viscosity
fluid retention
anemia
How is TPR determined?
4 listed
