Lecture 5 Arteries Flashcards
What is blood flow?
Blood flow is the quantity of blood that passes a given point in the circulation in a given period of time
What is overall blood flow in the circulation of an adult?
5 liters per minute
How is velocity of blood flow determined, and what proportional relationship exists for blood velocity?
Velocity = blood flow / cross sectional area.
As cross section size increases, velocity increases.
What are the determinants of blood flow?
Pressure difference between two ends of the blood vessel and resistance of the vessel - give by Ohm’s Law, F = delta P / R.
How to calculate resistance for parallel circuit?
1/resistance = 1/R1 + 1/R2…
What is laminar flow?
How the blood in vessels flows in streamlines, with a parabolic profile - velocity in the center is greatest due to reduced resistance
What are 4 causes of turbulent flow?
- High velocities
- Sharp turns
- Rough surfaces
- Obstruction eg rapid narrowing of a vessel
How to tell laminar and turbulent flow apart? What can turbulent flow diagnose?
Laminar is silent, turbulent flow causes murmurs.
Murmurs (bruits) diagnose vessel stenosis, vessel shunts, and cardiac valvular lesions.
How can we measure turbulent flow?
By using Reynold’s number, which is the tendency of turbulence to occur.
(Re 200-400 branches, 2000 in straight vessel)
What blood vessels always have turbulent flow and why?
Proximal portion of aorta and pulmonary artery because high velocity, pulsatile flow, elastic walls, valve movement.
How does atherosclerosis cause turbulence?
Rough surface from plaques
How does aneurysm cause turbulence?
No longer straight vessel, large open space causes change in diameter and direction
How could we calculate the resistance of a vessel?
Diameter to the power of four (d^4).
What is blood pressure?
The force exerted by the blood against any unit area of the vessel wall.
What are the systolic and diastolic pressures referring to?
Systolic - height of the pressure pulse, 120mmHg
Diastolic - lowest point of the pressure, 80mmHg
What is pulse pressure?
Difference between systolic and diastolic pressure
What does a pressure pulse contour look like for arteriosclerosis?
Increase in pulse pressure since the pressure is not being absorbed by the elasticity of the aorta. Very high spikes.
What does a pressure pulse contour look like for aortic stenosis?
Reduced aortic valve opening reduces blood flow so low systolic pressure flattens out pressure contour.
What does a pressure pulse contour for aortic insufficiency look like?
Larger pulse pressure with no dips due to incomplete closing of aortic valve, excessive turbulence, regurgitation.
What do you listen for during the Auscultatory method for measuring blood pressure?
Korotkoff sounds
Why does blood pressure raise with age?
Arteries are less compliant and elastic so less pressure is absorbed by the elastic arteries.
Why is mean blood pressure closer to diastolic pressure?
Systole is very fast, not much time spent there - spend more time in diastole.
