Haemodynamics

Question 1

Explain the difference between plasma and serum

Answer 1

Serum is blood that clots, plasma does not clot

Serum = plasma - clotting factors

Question 2

What is peripheral resistance

Answer 2

Totality of resistance of the heart

Question 3

How does blood viscosity mainly increase

Answer 3

Increase in red blood cells (polycythaemia), platelets (thrombocythaemia) or white blood cells (leukaemia) can lead to increased whole blood viscosity and sludging in blood in peripheries

Question 4

How can minor changes in plasma viscosity occur

Answer 4

Minor changes in plasma viscosity can result from raised levels of acute phase plasma proteins (fibrinogen, complement factors and C-reactive protein)
Acute phase proteins increase in response to inflammation and thus minor changes in plasma viscosity can be used to measure the inflammatory response
C-reactive protein concentration also used to measure inflammation

Question 5

Explain laminar and turbulent flow

Answer 5

For laminar, velocity greater in middle than periphery
Blood usually flows in streamlines in laminar flow
Turbulent occurs: when rate of blood flow is too great
When it passes by an obstruction in a vessel
When it makes a sharp turn
When it passes over a rough surface
Eg. anaemia - blood pumps faster and causes increase flow

Question 6

Equation of pulse pressure

Answer 6

Pulse pressure = (peak systolic pressure - end diastolic pressure)

Question 7

Equation of mean arterial pressure

Answer 7

Mean arterial pressure can be estimated as (diastolic pressure + 1/3 of pulse pressure)
If mean arterial pressure falls below 70 mmHg, then organ perfusion is impaired

Question 8

Explain significance of dicrotic notch

Answer 8

Aortic valve shuts at dicrotic notch, where systole ends

Question 9

Explain relationship between velocity and flow

Answer 9

As velocity increases, flow decreases

Question 10

What is bruit

Answer 10

A noise heard through a stethoscope

Question 11

How does pulse occur

Answer 11

When flow is not constant - shock wave felt slightly before the blood itself

Question 12

What determines strength of volume of pulse

Answer 12

Force with which the left ventricle is able to eject blood into the arterial system and thus develop a normal shock wave

Pulse pressure - greater the pulse pressure, the stronger the pulse

Question 13

What causes thready pulse

Answer 13

Left ventricular failure, aortic valve stenosis, hypovolaemia (severe dehydration, bleeding)

Question 14

What causes bounding pulse

Answer 14

Bradycardia - lower diastole pressure

Low peripheral resistance means blood rushes out faster