Haemodynamics

Question 1

What is the fluid collected from unclothed blood called?

Answer 1

Plasma is the main fluid

Buffy Coat and RBCs are also present once centrifuged

Question 2

What is the fluid collected from clotted blood called?

Answer 2

Serum is the main fluid

Forms when fibrin is precipitated out.

Clot remains at the bottom of test tube

Question 3

What happens when heparin is added to blood Vs when there is no herparin?

Answer 3

When you add heparin, the blood does not clot

When there is no heparin fibrin precipitates out and serum is formed.

Question 4

What is serum?

Answer 4

Serum = plasma minus clotting factor (the main clotting factor being fibrinogen)

Question 5

The heart is a closed circuit. True or false?

Answer 5

True

Question 6

What is the peripheral resistance?

Answer 6

The totality of resistance posed to the ejecting heart

Question 7

What is the biggest determinant of peripheral resistance?

Answer 7

The state of contraction of the resistance arterioles

Question 8

How does whole blood viscosity increase? What is the consequence of this increase?

Answer 8

Marked increase in plasma viscosity can lead to increased whole blood viscoslty and sludging of blood in peripheries.

The commonest cause by far is multiple myeloma which is cancer of plasma cells.

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

Heart finds it hard to push to the peripheries when the viscosity increases.

Viscosity also increases with coolness and the peripheries are cool.

Question 9

Why can plasma viscosity be used to measure the inflammatory response in infection?

Answer 9

Minor changes in plasma viscosity can result from raised levels of acute phase plasma proteins (e.g. Fibrinogen, Complement factors and C-reactive protein).

These acute phase proteins increase in response to inflammation.

Therefore, minor changes in plasma viscosity can be used to ‘measure’ the inflammatory response.

In recent years, we have been able to measure C-reactive protein (CRP) and this is more commonly used to ‘measure inflammation’

Question 10

What is the pressure gradient in blood?

Answer 10

Fluids move from regions of high pressure to regions of low pressure.

Question 11

What is the difference between laminar and turbulent flow?

Answer 11

Laminar - sheets and lines - because of the effect of friction the velocity of the blood cells will be greater in middle than periphery because in the periphery the cells will be in contact with the wall.

Turbulent - all over the place and the blood flow is continually mixing

Question 12

What are the characteristics of blood flow?

Answer 12

It flows in streamlines (LAMINAR FLOW)

Question 13

What is a parabolic profile?

Answer 13

When laminar flow occurs, the velocity of blood in the centre of the vessel is greater than that toward the outer edge. This creates a parabolic profile where the centre of blood flow moves at a great speed/velocity.

It looks like an arrow like image.

Question 14

When do we see turbulent Blood flow? (5)

Answer 14

• When the rate of blood flow becomes too great (in anaemia, less o2 so heart pumps harder to compensate and get o2 to major organs.)
• When it passes by an obstruction in a vessel
• When it makes a sharp turn
• When it passes over a rough surface (atheroma)
• Increased resistance to blood flow

Question 15

What is the difference between an occlusion and stenosis?

Answer 15

An occlusion is a blockage

A stenosis is narrowing of vessels

Question 16

What is Haemodynamics?

Answer 16

The study of the effect that pressure might have on flow through blood vessels.

Question 17

What units do you measure flow in?

Answer 17

Volume per unit of time

Question 18

What is the measure of pressure?

Answer 18

Pounds per square inch

Question 19

Explain compliance in blood vessels.

Answer 19

This is when a vessels volume can change in response to pressure.

Question 20

What happens if you have one stenosis followed by another stenosis?

What is the clinical term?

Answer 20

The flow stops.

This is because the first stenosis causes a decrease in pressure beyond the stenosis so when another stenosis forms later on, the flow stops altogether.

Each stenosis reduces the pressure beyond it and it gets worse and worse.

This is called critical ischaemia.

Question 21

What happens to arteries beyond a stenosis?

Answer 21

It will get bigger - this enlargement is called an aneurism.

You will get a post-stenotic dilitation

Question 22

What is the consequence of increase in age and calcification of arteries.

Answer 22

As people get older their arteries calcify.

This means the artery will have no compliance so you can’t feel a pulse at the point of calcification.

Question 23

How can you check if an artery has a stenosis in it?

Answer 23

Hear it - “Bruit”

Feel it - ‘Thrilling’

Question 24

When do you hear a murmur?

Answer 24

You hear it across a heart valve with a stenosis

Question 25

What effect does a stenosis have on the pressure and velocity of an artery?

Answer 25

It causes an increase in velocity but a decrease in flow

Question 26

What is the relationship between kinetic energy, flow and velocity.

Answer 26

Kinetic Energy = 1/2 X mass X velocity(squared)

So as the velocity increases, the energy increases.

As velocity and energy increases, flow decreases.

Question 27

What is the anacrotic limb?

Answer 27

Ana = up, krotos = beat

Question 28

Using the terms, systole, diastole, anacrotic limb and diacritic limb, explain what a descending aorta pressure tracing would look like and why.

Answer 28

It starts with systolic uptake
- during systole, the pressure in the left ventricles in higher and so when the ventricles contracts, the blood rushes into the aorta which begins to stretch and so the pressure in the aorta increases. This is the anacrotic limb.

This occurs until the peak systolic pressure is reached.

Then there is systolic decline as the left ventricular pressure starts to decrease. The pressure then comes down until the aortic valves snap shut and no more blood can enter it. This is the dictotic notch.

Diastolic run off occurs after the aortic valve closes as diastole begins here.

Question 29

What is the pulse pressure?

Answer 29

The difference between the Peak systolic pressure and the end diastolic pressure.

Because of the way we measure BP with a sphygomanometer
means that:
Pulse pressure = (systolic pressure – diastolic pressure).
Therefore most commonly, pulse pressure is (120mm Hg – 80 mm Hg) = 40mm Hg

Question 30

What is the diacritic notch?

Answer 30

The point at which the aortic valve shits and thus where systole ends.

Question 31

What is the mean arterioles pressure?

Answer 31

The area under the curve in a heart tracing.

Question 32

What is the mean arterial pressure?

Answer 32

Mean arterial pressure can be estimated as (diastolic pressure + 1/3 of the pulse pressure).

Therefore most commonly, mean arterial pressure is
(80 mmHg + 13 mmHg) = 93 mm Hg.

Question 33

What happens if mean arterial pressure falls below 70mmHg and 60mmHg?

Answer 33

If mean arterial pressure falls below 70 mm Hg then organ perfusion is impaired.

If below 60 mM Hg, then it is extremely bad. Fatal.

Question 34

Why is there reverse flow in diastole?

Answer 34

Retrograde flow in the arterial system can occur and is greatest when the peripheral resistance is high – the blood ‘bounces back’

Question 35

When you feel a pulse what are you feeling?

Answer 35

A shock wave that arrives slightly before the

blood itself

Question 36

What two things determine how strongly a pulse is felt?

Answer 36

1) The force with which the left ventricle is able to eject blood into the arterial system and thus develop a normal shock wave.

Reduced pulse volume can result from left ventricular failure, aortic valve stenosis, hypovolaemia (severe dehydration, bleeding).

Such a pulse is weak and so is often described as “thready”

2) The pulse pressure. The greater the pulse pressure the stronger the pulse. A really strong pulse is often described as ”bounding”

Question 37

What are the causes of a bounding pulse? Explain them.

Answer 37

Because the pulse pressure is widened.

1) Bradycardia, such as heart block, widens pulse pressure and leads to a bounding pulse

If heart slows down, diastole has more time to occur and so the pressure in diastole is lower.

If the pressure is lower, the pulse pressure goes up

2) Low peripheral resistance (hot bath, exercise, pregnancy)
lowers diastolic pressure and therefore increases pulse pressure

Question 38

Why do you get a low peripheral resistance when you’re pregnant?

Answer 38

Because a boiler in uterus is producing heat and you need to get rid of the heat via vasodilation.

The vasodilation leads to reduced peripheral resistance

Question 39

Why is it important to use the correct cuff size when measuring blood pressure?

Answer 39

The cuff must go around at least 80% of the patients arm.

If cuff is too small, it gives a falsely higher BP therefore it is very important

Question 40

What is the pulse obliteration pressure?

Answer 40

The systolic pressure, when the pulse disappears

Question 41

What is the difference between the Korotkoff sounds in BP measurement at phase 1 and 5?

Answer 41

Phase 1 - systolic pressure - when you hear the first sound

Phase 5 - when sound disappears - this indicates diastolic blood pressure

Question 42

What is the effect of gravity on arterial and venous pressure?

Answer 42

If standing, the pressure in foot is 80mm Hg greater than in heart.

BP must be measured when patient is recombinant so the heart is same level as their ankle.

If BP is measured with hand up, BP will be too low

Venous pressure affected by gravity.

Neurosurgery - patient sitting to avoid air embolism