3. Haemodynamics

Question 1

what are the constituents of blood?

Answer 1

Whole blood is made up plasma (serum), white blood cells, platelets and red blood cells.

Question 2

what is serum?

Answer 2

Serum is plasma without clotting factors

Question 3

What is the the effect of changing cell number or protein content on viscosity?

Answer 3

Blood viscosity is relatively unchanging, it will only occur as a result of conditions such as polycythaemia, thrombocythaemia or leukaemia.
These can lead to “sludgey” thick blood – leading to dry
gangrene in peripheries.
However minor changes in plasma viscosity are more common.
They’re usually due to plasma proteins e.g fibrinogen, compliment and C-reactive protein. – used to measure plasma viscosity as indicator of inflammation

Question 4

what is Polycythaemia?

Answer 4

An abnormal increase in the concentration trait on of haemoglobin in the blood

Question 5

what is Thrombocythaemia?

Answer 5

An abnormal production of the cell that produce blood platelets (megakaryocytes) which leads to an excess of platelets to in the blood.

Question 6

what is Leukaemia?

Answer 6

Disease that causes the bone marrow and other blood forming organs to produce abnormal leukocytes.

Question 7

what is haemodynamics?

Answer 7

Haemodynamics can be defined as the factors that govern blood flow (the movement of fluid between two points) and are dependent upon the relationship between cardiac output, blood pressure and resistance

Question 8

how does pressure affect blood flow?

Answer 8

Blood moves from relative high to low pressure regions

Question 9

what are the 2 types of blood flow?

Answer 9

laminar flow

turbulent flow

Question 10

Differentiate between the 2 types of blood flow

Answer 10

In laminar flow adjacent layers of blood slide over each other. Flow will be fastest in the central layers and slowest in the peripheral layers.
Laminar flow is silent, smooth, streamlined and organised. It maintains energy and is the more common type of flow through the vessels.

Turbulent flow is noisy, disorganised,non streamlined flow. Energy is lost and can be a sign of pathology.

Question 11

when does blood flow change from laminar to turbulent?

Answer 11

when there is occlusion of a blood vessel, whether due to a stenosis or atherosclerotic build up. change in diameter of vessel causes disruption resulting in turbulent flow. Blood flow can also change to turbulent when there is change in vdirection of vessels (branching)

Question 12

What is the difference between the two types of blood flow graphically?

Answer 12

As the perfusion pressure increases, laminar flow increases linearly.
When the laminar flow changes to turbulent flow, it is the critical point at which the pressure increase beyond which flow can match it linearly, so the line curves. If the flow can’t increase proportionally to perfusion pressure, from that point, flow is turbulent.

Question 13

what is flow?

Answer 13

volume transferred per unit

time – (L/min)

Question 14

what is pressure?

Answer 14

force per unit area –
(mmHg used as surrogate when
measuring BP – SI unit is Pascal)

Question 15

what is resistance?

Answer 15

measure of difficulty of flow

Question 16

how does resistance affect flow?

Answer 16

Flow is inversely proportional to flow. At high resistance, flow is decreased so pressure difference has to increase. At low resistance, flow is increased as pressure increases.
An increase in resistance causes a reduction in flow.

Question 17

what are the factors that act as resistance to flow?

Answer 17

Primary factors are diameter, length of vessel and viscosity - physiologically diameter is most important quantitatively – vessel length (L) doesn’t change and viscosity (η) of blood regulated within narrow range.

The radius and changes in the radius of a vessel have a large impact on flow and or resistance.

Question 18

What effect does an increase in resistance and a maintenance of the flow level have on pressure?

Answer 18

If resistance increases and flow is maintained pressure will have to rise to overcome this resistance.

Question 19

What effect do changes in pressure have on resistance and vice versa?

Answer 19

A change in pressure will indicate a change in resistance.
So for example an increase in pressure suggests that there’s been an increase in resistance whilst a decrease in pressure indicates a decrease in resistance in vessels.In the arterial system, as resistance increases, blood pressure increases and flow decreases.

Question 20

Compare the resistance in arteries and arterioles and give the structures of each that result in this

Answer 20

• There’s a lower resistance in the larger arteries such as the aorta in comparison to smaller arteries and the arterioles.
• This is due to the fact that larger arteries have a larger diameter and a wider lumen so the resistance to blood flow isn’t as monumental.
• However arterioles have a smaller lumen and smaller diameter resulting in a larger resistance in these areas.
• the pressure in arterioles is much smaller despite the increase in resistance as he cross sectional area increases.
• Smallest arteries and arterioles contribute greatest component of total peripheral resistance – biggest jump in pressure across vessel class

Question 21

Compare the resistance in pulmonary circulation vs systemic circulation and explain why this is

Answer 21

Resistance in the pulmonary circulation is much lower than systemic system.
This is because vessels in the pulmonary system have shorter and wider vessels so the the level of resistance and pressure will be lower than in the systemic circulation.

Question 22

what is velocity?

Answer 22

Velocity (V) is distance fluid (blood) moves in a given time (cm/s)

Question 23

what are the factors affecting velocity of blood?

Answer 23

Velocity is related to flow and will be affected by the cross-sectional area of the vessel.

As the total cross-sectional area of the vessels increases, the velocity and flow decreases. This is why blood flow is slowest in the capillaries, which allows time for exchange of gases and nutrients.
At constant flow, V is inversely related to r2

Question 24

Compare velocity to cross-sectional area and relate this to different blood vessels

Answer 24

Velocity (the distance blood travels in a given time) will vary based on the cross-sectional area of the vessel it’s in.
As the total cross-sectional area of the vessels increases, the velocity of flow decreases.

In the capillaries you have a very large cross-sectional area, here the velocity is a lot slower than at the aorta or any of the large arteries.
This is to allow allows time for exchange of gases and nutrients.
However as you leave the capillaries and move into the larger veins and the vena cava you’ll see a reduction in area and an increase in velocity.

Question 25

what is pulse pressure?

Answer 25

Pulse pressure is the difference between systolic and diastolic blood pressure. It represents the force that the heart generates each time it contracts.

Question 26

what governs pulse pressure?

Answer 26

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

Question 27

what is the equation for pulse pressure?

Answer 27

Pulse pressure (PP) = systolic blood pressure (SBP) – diastolic blood pressure (DBP)

Question 28

which factors affect pulse pressure?

Answer 28

1. Exercise Exercise will cause an increase in stroke volume which causes an increase in pulse pressure. increase in systolic blood pressure 2. Haemorrhage 3. Age Age often results in the development of atherosclerosis, this'll cause an increase in systolic pressure and therefore an increase in pulse pressure. 4. Heart block Causes a strong pulse and an increase in pulse pressure as there is bradycardia so the longer beat means extra reduction of diastolic pressure and thus fresher difference between SP and DP. 5. Vasodilation Causes a decrease in peripheral resistance, a strong pulse and an increase in pulse pressure

Question 29

what is mean arterial pressure?

Answer 29

The mean arterial pressure (MAP) is an average blood pressure in an individual during a single cardiac cycle.

Question 30

what is the equation for mean arterial pressure?

Answer 30

Mean arterial pressure (MAP) = DBP + (SBP-DBP)/3) = DBP + 1/3 PP MAP = CO x Total peripheral resistance (TPR)

Question 31

what is cardiac output and what is its equation?

Answer 31

``` Cardiac output is the volume of blood ejected from the left side of the heart in one minute.Total flow is the cardiac output Cardiac output (CO) = Heart rate (HR) x Stroke volume (SV) ```

Question 32

what is the stroke volume?

Answer 32

Stroke volume (SV) is the volume of blood pumped from the left ventricle per beat

Question 33

what is heart rate?

Answer 33

Heart rate is the speed at which the heart beats

Question 34

What is a pulse ?

Answer 34

A pulse is a shock wave that arrives slightly before the blood itself.

Question 35

what can the pulse pressure be described as?

Answer 35

Described as a “bounding” pulse

Question 36

what is increasing pulse pressure common in?

Answer 36

* Heart block – bradycardia * Vasodilatation – decrease peripheral resistance – hot bath, pregnancy * Elite athletes – systolic increased and diastolic decreases

Question 37

How can blood pressure be measured?

Answer 37

• The measurement of blood pressure relies on changes in blood flow. • A cuff is placed over the brachial artery in the arm and is inflated until blood can no longer pass through, this is the systolic pressure. • This inflation causes an occlusion of the vessel which causes a change in blood flow from laminar to turbulent. This change creates sound known as Korotkoff sounds. • Once systolic pressure has been identified the cuff will deflate to reduce the pressure on the brachial artery. • This will continue until the turbulent flow is now laminar and no more sounds can be heard. This is the diastolic pressure.

Question 38

what happens when blood flow changes from laminar to turbulent?

Answer 38

* Velocity increases and flow decreases beyond stenosis * Thrill can be felt * Bruit can be b heard

Question 39

What carrying out a blood pressure measurement give the factors that have to be considered

Answer 39

1. The size of the cuff If the cuff is too small you get an overestimation of BP but if the cuff is too big you get an underestimation of BP. 2. The positioning of the cuff You have to know the position of the brachial artery to be able to carry out the measurement properly. 3. You need to measure in both arms There's often a difference in the 2 so you'd use the higher as a reference 4. Positioning of the patient The patient should be sat comfortably with their legs uncrossed and flat on the ground and their arm supported. Unless otherwise stated, assumed that measurement will be taken at the level of the heart and RESTING 5. Repetition BP measurement should be repeated several times and a mean should be taken of the 2 closest values

Question 40

Give the effects of gravity on BP

Answer 40

• The pressure below the level of the heart is greater in comparison to the pressure above the level of the heart which is lower. • Gravity creates a pressure gradient that allows blood to flow from the heart to the foot when standing. • Pooling of blood occurs below the level of the heart upon standing in the venous system • Postural hypotension – dizziness upon standing – ↓stroke volume → transient arterial hypotension - decrease in blood pressure by a sudden change in position

Question 41

Explain how arterial pulse is generated

Answer 41

Pulse, rhythmic dilation of an artery generated by the opening and closing of the aortic valve in the heart.