Week 3 - Lesson 1 (Part 7) Flashcards
What does collateral flow arise from?
Ischemia in the presence of atheromatous disease
- re-routing due to blockages
Ischemia
No oxygen to the tissues which result in cell death
Collateral flow
Circulation to tissue or an organ can be maintained using a different pathway
- occurs over time
Anastomosis
Branches form between adjacent blood vessels
- connection between 2 veins
Where can collateral circulation be established? (2)
- In the venous system
- between veins - In the arterial system
- between arteries
What is an example of collateral flow?
Blood flow to the brain is maintained through a network of collaterals that anastomose in the circle of Willis
What compensatory mechanisms come into play in an attempt to preserve perfusion during atherosclerosis? (3)
- Development of a collateral circulation
- A degree of local dilatation of the affected arterial segment
- An increase in the extraction efficiency of oxygen from blood
What is one factor used to control the flow rate to the organ?
The degree of constriction of distal arterial bed
What happens to flow rate as the resistance to flow of diseased arteries increases?
It is maintained within normal levels as a result of arteriolar dilatation
What are very high degrees of stenosis are accompanied by? (2)
- Low flow rate
- Low velocities
- damped and trickle flow
What are 3 types of flow waves?
- Triphasic
- Biphasic
- Monophasic
What are 2 types of beds?
- Low resistant bed
2. High resistant bed
What is an example of a low bed resistance? (7)
- Brain
- Kidneys
- Liver
- Vertebral arteries
- Distal ICA
- Ovaries
- Testicles
What is an example of a high bed resistance? (3)
- Muscles at rest
- Arms and legs
- peripheral circulation - Small intestines
- not during digestion
Low resistance beds
Structures with metabolic processes that needs continuous forward flow throughout the cardiac cycle
What do muscles need during exercise?
A high rate of oxygen exchange
How are high resistant beds characterized? (3)
- Low
- Absent
- Reversed flow during diastole
Where is a triphasic waveform normally found?
In arteries supplying a high resistance peripheral vascular bed
What is the normal sonographic appearance of a triphasic waveform? (3)
- Highest pulsatility
- Highest resistance waveform
- 3 points in the pulse
What is an example of a triphasic waveform? (2)
- ECA
2. Femoral artery
What happens to flow reversal with vasoconstriction in triphasic waveforms?
It increases
What does the first initial spike mean in triphasic flow?
Forward flow in systole
What does the second spike mean in triphasic flow?
Diastolic flow reversal
What does the third spike mean in triphasic flow?
Forward flow in late diastole
What kind of wave is forward flow?
Reflective wave
What kind of flow happens during systole?
Forward flow throughout the periphery
What kind of flow happens during diastole?
Temporary flow reversal
Why does temporary flow reversal occur during diastole?
Because of a negative pressure gradient caused by peripheral resistance to forward flow
What does flow reversal decrease with? (3)
With increasing…
- Vasodilation as in exercise
- Body heating
- Stenosis
What does flow reversal increase with?
Vasoconstriction
What are the 3 components of flow?
- Forward flow in systole
- Diastolic flow reversal
- Forward flow in late diastole
