Session 1: Haemodynamics

Question 1

What do whole blood viscosity changes indicate?

Answer 1

Polycythaemia, thrombocythaemia or leukaemia.

Sludgey thick blood leading to dry gangrene in peripheries

Question 2

What do minor changes to plasma viscosity indicate?

Answer 2

Typically from acute phase plasma proteins like fibrinogen, compliment and CRP as a result of inflammation.
This means plasma viscosity can be used to indicate inflammation. However typically measured by CRP levels.

Question 3

What two main types of flow are there?

Answer 3

Laminar flow

Turbulent flow

Question 4

What is laminar flow?

Answer 4

Smooth and silent flow which is going parallel. Energy is well conserved.

Question 5

What is turbulent flow?

Answer 5

Disorganised flow with no real structure. Turbulent flow is noisy.

Question 6

Why would turbulent flow occur?

Answer 6

Because of a narrowed blood vessel or valve.
If the pressure increase beyond which flow can match it linearly turbulent flow can occur.
This is likely to occur in ventricles and stenosed arteries.

Question 7

What is flow?

Answer 7

Volume transferred per unit time (L/min)

Question 8

What is pressure? What is it measured in?

Answer 8

Force per unit area measured in mmHg.

Question 9

Flow = K(P1-P2) where K is conductance.

What is conductance?

Answer 9

Measure of ease of flow.

Question 10

R = (P1-P2)/Flow or Flow = (1/R) x (P1-P2) where R is resistance.
What is resistance?

Answer 10

Measure of difficulty of flow and reciprocal to conductance.

Question 11

Darcy’s law.

Answer 11

Flow = (P1-P2)/R

Question 12

What happens if resistance increases and flow is still maintained?

Answer 12

Pressure difference has to rise.

Question 13

What is the seat of total peripheral resistance?

Answer 13

Arterioles

Question 14

Give formula for pulse pressure.

Answer 14

PP = SBP - DBP

SBP = Systolic blood pressure
DBP = Diastolic blood pressure

Question 15

Man comes in with 130mmHg over 60 mmHg.
What is his SBP?
What is his DBP?
What is his PP?

Answer 15

SBP = 130 mmHg
DBP = 60 mmHg
PP = 130 - 60 = 70 mmHg

Question 16

Give formula for mean arterial pressure.

Answer 16

MAP = DBP + (SBP-DBP)/3
or
MAP = DBP + 1/3PP
or
MAP = 2/3DBP + 1/3SBP

Question 17

At what MAP will organ perfusion become impaired?

Answer 17

Below 70 mmHg

Question 18

Definition of pulse pressure.

Answer 18

Volume of blood ejected and the compliance of the arterial system govern pulse pressure.

Question 19

What will happen if there is an increase in stroke volume during exercise?

Answer 19

An increase in pulse pressure.

Question 20

What happens to pulse pressure during haemorrhage?

Answer 20

It decreases

Question 21

What happens to pulse pressure at age during atherosclerosis?

Answer 21

It increases

Question 22

Formula for cardiac output.

Answer 22

CO = SV x HR

Question 23

How does MAP relate to cardiac output?

Answer 23

MAP = CO x TPR
MAP = SV x HR x TPR

Question 24

What is a bounding pulse?

Answer 24

Increased pulse pressure also called strong pulse.

Question 25

What causes bounding pulse/strong pulse/increased pulse pressure?

Answer 25

Anything which will either increase systolic pressure or decrease diastolic pressure.

Heartblock leading to bradycardia
Vasodilation leading to decreased peripheral resistance
Elite athletes with increased systolic.

Question 26

In R = (P1-P2)/Flow

What does each variable signify in terms of systemic circulation?

Answer 26

Total flow is the cardiac output
The pressure difference (P1-P2) is mean aortic pressure (P1) minus central venous pressure CVP (P2)
R is the systemic resistance also called total peripheral resistance (TPR)

Question 27

What is mean arterial pressure determined by?

Answer 27

Cardiac output and total peripheral resistance
MAP = CO x TPR
This is from 
TPR = (MAP - CVP)/CO
Where CVP is near to 0 because it's low
This leaves TPR = MAP/CO
MAP = TPR x CO

Question 28

Factors determining resistance to flow.

Answer 28

Diameter, length of vessels
Viscosity of blood

Physiologically diameter is most important.

Question 29

Where is the site of resistance and why?

Answer 29

In arterioles and terminal arteries because they have a smaller diameter.

Question 30

But capillaries have smaller diameter than arterioles. Why is resistance not higher here?

Answer 30

Because capillaries are connected in a parallel manner. In parallel the conductance is additive (1/R1+ 1/R2 etc…) where 1/R = K aka conductance.

Question 31

What is thrill?

Answer 31

Change in blood flow that can be felt

Question 32

What is bruit?

Answer 32

Change in blood flow that can be heard

Question 33

Explain the process of manual blood pressure taking.

Answer 33

We create a turbulent flow and auscultating.
The changes from laminar to turbulent flow when you start to release pressure caused by the strap.
The changes from laminar to turbulent can be heard and are also known as korotkoff sounds.
When turbulent goes to laminar again the sound will disappear.

Question 34

How do you know which is the SBP and DBP?

Answer 34

SBP is the pressure of which the first sound heard

DBP is the pressure of which there is no sound left

Question 35

What is important to consider in blood pressure by auscultation?
Technique-wise.

Answer 35

Cuff size. Too small will overestimate
Too big will underestimate

Position of cuff
Measure in both arms
Sat comfy with legs uncrossed and flat on the ground.
Arm supported
Repeated several times

Question 36

How does gravity affect blood pressure?

Answer 36

Pressure below level of heart is greater

Pressure above the level of the heart is lower.