Flashcards in CVS - Haemodynamics Deck (17)
What is the difference between plasma and serum?
Fluid from unclothed blood is "plasma", fluid from clotted blood is "serum".
Serum = plasma without clotting factors.
What is peripheral resistance?
The resistance of the arteries to blood flow. As arteries contract, resistance increases. As they dilate, resistance decreases.
Give the commonest cause of increased plasma viscosity.
What is blood viscosity?
The resistance of blood to flow (aka the thickness/stickiness of blood).
What is the difference between turbulent and laminar flow of blood?
Laminar - flows in sheets/lines in one direction
Turbulent - blood flowing in all directions in the vessel
How does laminar flow affect the velocity of blood in the vessel?
The velocity of blood in the centre of the vessel is greater than that toward the outer edge, creating a parabolic profile.
When might turbulent blood flow occur?
- rate of blood flow becomes too great
- blood passes an obstruction in the vessel
- blood makes a sharp turn
- blood passes over a rough surface
- increased resistance to blood flow
What causes the "dicrotic notch" in a descending aorta pressure tracing?
Aortic valve shutting
How is pulse pressure calculated?
Peak systolic pressure minus end diastolic pressure.
Eg 120mm Hg - 80mm Hg = 40mm Hg
How is mean arterial pressure estimated?
Diastolic pressure + 1/3rd of the pulse pressure
Eg 80mm Hg + 13mm Hg = 93mm Hg
What happens if mean arterial pressure falls below 70mm Hg?
Organ perfusion is impaired
What is the cause of the physical feeling of a pulse?
A shock wave that arrives slightly before the blood itself.
What two things determine the 'volume' of the pulse?
- the force that the left ventricle is able to eject blood with
- the pulse pressure
Give one cause of a bounding pulse.
Bradycardia widens pulse pressure and leads to a bounding pulse
How does peripheral resistance affect diastolic pressure?
Vasodilation of arterioles (low peripheral resistance) causes a low diastolic pressure. Vasoconstriction of arterioles (high peripheral resistance) causes a high diastolic pressure
How many phases of sounds are heard when measuring blood pressure?
Phase 1 - tapping sound appears
Phase 2-4 - various other sounds
Phase 5 - silence