Haemodynamics

Question 1

What is the major function of the vascular system?

Answer 1

Maintain blood pressure

Question 2

What is haemodynamics?

Answer 2

The physical factors that govern blood flow

Flow depends on pressure gradient and resistance

Question 3

What is blood flow?

Answer 3

Quantity of blood passing a given point in the circulation in a given period
ml/min

Question 4

What is the normal blood flow in an adult?

Answer 4

5000ml/min

= CO

Question 5

What is the equation for blood flow?

Answer 5

F = change in pressure/resistance to flow

Question 6

What are the factors affecting flow?

Answer 6

Laminar vs Turbulent flow

Resistance of the vessels (series vs parallel)

Question 7

Name the 3 patterns of blood flow.

Answer 7

Laminar
Turbulent
Bolus

Question 8

Which vessels undergo laminar flow?

Answer 8

Most arteries, arterioles, veins and venules

Question 9

Which vessels undergo turbulent flow?

Answer 9

Ventricles, sometimes aorta, atheroma

Question 10

Which vessels undergo bolus flow?

Answer 10

Capillaries

Question 11

What is laminar flow?

Answer 11

Different layers flow at different rates creating a parabolic profile.
Sliding motion of one laminar layer over another = shear

Question 12

What causes shear stress?

Answer 12

Friction of molecules rubbing against each other

Question 13

What causes increased shear stress and what results of it?

Answer 13

HTN, atheroma, Marfan’s syndrome
High shear stress at proximal aorta results in dissecting aortic aneurysm
High shear stress can tear the endothelium

Question 14

What is turbulent blood flow?

Answer 14

When the pressure driving the fluid is progressively increased
Flow no longer increases linearly
Increases as the square root of the pressure

Question 15

What is the critical value for the Reynold number?

Answer 15

2000

Question 16

What is the Re of most blood vessels?

Answer 16

Less than the critical value of 2000

Question 17

Name where/in what circumstances the Re is normally high in.

Answer 17

Left ventricle - mixes the blood to produce uniform gas content
Aortic root - during peak ejection, increased diameter of blood vessel
Exercise - increase velocity
Pregnancy - high CO and reduced viscosity
Anaemia - reduced viscosity

Question 18

How can turbulent blood flow be detected in the heart and in the vessels?

Answer 18

Heart = murmur 
Vessels = bruit

Question 19

When is the Re pathogenically increased?

Answer 19

Atherosclerotic blood vessels

Question 20

How does resistance influence flow?

Answer 20

Increase resistance = decrease flow

Decrease resistance = increase flow

Question 21

Name the 3 factors governing resistance.

Answer 21

Length of tube (L)
Viscosity of liquid
Radius of tube

Question 22

What is the main site of resistance in the CVS system?

Answer 22

Arterioles and smallest arteries

= the biggest pressure drop occurs between the conduit arteries and the arterial end of the capillaries

Question 23

How is the pulmonary circuit arranged differently to the systemic circuit?

Answer 23

Pulmonary circuit is arranged in series

Systemic circuit is arranged in parallel

Question 24

What is the importance of having a parallel series in the systemic circulation?

Answer 24

Guarantees all tissues receive fresh oxygenated blood

Allows independent variation of blood flow through different organs depending on their need

Question 25

Which organs receive the most blood flow at rest?

Answer 25

Skeletal muscle
Abdominal organs
Kidney

Question 26

What happens to blood flow during exercise?

Answer 26

Decrease blood flow to gut and kidneys

Increase blood flow to skeletal muscle, skin and heart

Question 27

What is the function of the aorta and large arteries with regards to flow and pressure?

Answer 27

Reduce the fluctuations in flow and the pressure generated by the intermittent ejection of SV.
Accomplished by the highly elastic walls of these vessels.

Question 28

Describe what happens to the elastic elements of the aorta and large arteries in systole and diastole.

Answer 28

During systole energy is stored in the vessel wall as the elastic fibres are stretched.
Energy is released during diastole.
This prevents large swings in BP between heart beats and results in a steady blood flow into smaller arteries.

Question 29

What is pulse pressure?

Answer 29

Systolic pressure - diastolic pressure

Question 30

What factors determine pulse pressure?

Answer 30

Stroke volume of the LV 
Arterial stiffness (reduced compliance) 
With atherosclerosis, compliance is reduced so pulse pressure can double with aging

Question 31

What are causes of a reduced pulse pressure?

Answer 31

Congestive heart failure
Severe haemorrhage
Aortic stenosis

Question 32

What are causes of an increased pulse pressure?

Answer 32

Well-trained athletes
Atherosclerosis
Aortic valve regurgitation

Question 33

When is blood pressure the lowest?

Answer 33

During sleep

Question 34

Name factors affecting arterial blood pressure.

Answer 34

Age
Posture: transient decrease in blood pressure
Sleep: decrease in BP
Emotions: anger fear = increase BP
Full bladder: increase BP
Valsalva manoeuvre
Smoking: increase in BP due to vasoconstriction
Haemorrhage and hypovolemia: decrease BP
Disease: HTN

Question 35

What is the function of veins?

Answer 35

Capacitance vessels - blood reservoirs

Due to high compliance - can release or store blood in response to small changes in pressure.

Question 36

Name the determinants of venous pressure.

Answer 36

Sympathetic innervation
Blood volume
Respiratory pump
Skeletal muscle pump

Question 37

What is varicose veins?

Answer 37

One-way valves of veins become leaky

Veins become dilated and tortuous