CVS - Haemodynamics

Question 1

What is the difference between plasma and serum?

Answer 1

Fluid from unclothed blood is “plasma”, fluid from clotted blood is “serum”.

Serum = plasma without clotting factors.

Question 2

What is peripheral resistance?

Answer 2

The resistance of the arteries to blood flow. As arteries contract, resistance increases. As they dilate, resistance decreases.

Question 3

Give the commonest cause of increased plasma viscosity.

Answer 3

Multiple myeloma

Question 4

What is blood viscosity?

Answer 4

The resistance of blood to flow (aka the thickness/stickiness of blood).

Question 5

What is the difference between turbulent and laminar flow of blood?

Answer 5

Laminar - flows in sheets/lines in one direction

Turbulent - blood flowing in all directions in the vessel

Question 6

How does laminar flow affect the velocity of blood in the vessel?

Answer 6

The velocity of blood in the centre of the vessel is greater than that toward the outer edge, creating a parabolic profile.

Question 7

When might turbulent blood flow occur?

Answer 7

• 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

Question 8

What causes the “dicrotic notch” in a descending aorta pressure tracing?

Answer 8

Aortic valve shutting

Question 9

How is pulse pressure calculated?

Answer 9

Peak systolic pressure minus end diastolic pressure.

Eg 120mm Hg - 80mm Hg = 40mm Hg

Question 10

How is mean arterial pressure estimated?

Answer 10

Diastolic pressure + 1/3rd of the pulse pressure

Eg 80mm Hg + 13mm Hg = 93mm Hg

Question 11

What happens if mean arterial pressure falls below 70mm Hg?

Answer 11

Organ perfusion is impaired

Question 12

What is the cause of the physical feeling of a pulse?

Answer 12

A shock wave that arrives slightly before the blood itself.

Question 13

What two things determine the ‘volume’ of the pulse?

Answer 13

• the force that the left ventricle is able to eject blood with
• the pulse pressure

Question 14

Give one cause of a bounding pulse.

Answer 14

Bradycardia widens pulse pressure and leads to a bounding pulse

Question 15

How does peripheral resistance affect diastolic pressure?

Answer 15

Vasodilation of arterioles (low peripheral resistance) causes a low diastolic pressure. Vasoconstriction of arterioles (high peripheral resistance) causes a high diastolic pressure

Question 16

How many phases of sounds are heard when measuring blood pressure?

Answer 16

5 phases

Phase 1 - tapping sound appears
Phase 2-4 - various other sounds
Phase 5 - silence

Question 17

How do you measure blood pressure?

Answer 17

• Inflate cuff etc (this includes brachial artery).
• Press stethoscope to crook of elbow.
• As cuff deflates, tapping sound appears - this is systolic pressure
• Eventually tapping sound stops - this is diastolic pressure