Intro and haemodynamics

Question 1

What is infarction?

Answer 1

Death of cells

Question 2

Capillaries are the sight of diffusion, what do they consist of?

Answer 2

A single layer of endothelial cells surrounded by basal lamina.

Question 3

Name 3 factors which affect diffusion

Answer 3

1. Area available for exchange - depends on capillary density.
2. Diffusion resistance - nature of molecule, barrier, path length.
3. Concentration gradient - depends on rate of use by tissues and rate of blood flow through capillary bed.

Question 4

What is capillary density?

Answer 4

Amount of capillaries in a tissue - higher capillary density at more metabolically active tissues.

Question 5

How does blood flow affect the concentration gradient?

Answer 5

Substances used by tissues have higher concentrations in arteries than capillaries. The lower the blood flow, lower capillary concentration. Blood flow has to be high enough to maintain a concentration gradient to drive oxygen diffusion into cells.

Question 6

What is perfusion rate?

Answer 6

Rate of blood flow.

Question 7

What type of blood flow is needed for: the brain, the heart, the kidneys and skeletal muscle and the gut.

Answer 7

The brain needs a constant high flow.
The heart needs a high flow which increases during exercise.
The kidneys need a high, constant flow.
The skeletal muscles can have a very high flow during exercise and the gut blood flow is highest just after a meal.

Question 8

What is the average cardiac output for a 70kg man?

Answer 8

5L/min at rest and can rise up to 25L/min during exercise.

Question 9

Where does the heart lie?

Answer 9

Between the 2nd and 5th intercostal spaces, behind the sternum in the pericardial sac situated in the media stinum (between lungs). The apex lines up with the left midclavicle line.

Question 10

What are the layers of the pericardial sac?

Answer 10

3 layers: outer fibrous layer attached to the first serous membrane of the parietal layer, then there’s the pericardial cavity containing a thin fluid for lubrication and then the visceral serous membrane (pericardium) which is attached to the myocardium.

Question 11

What is cardiac tamponade and what may need to be done in response to it?

Answer 11

If excess fluid builds up rapidly in the pericardial cavity, the heart is suppressed due to the inextensible fibrous layer of the pericardial sac. The heart won’t be able to relax and refill during diastole - medical emergency. Fluid may need to be removed to relieve pressure or for testing - pericardiocentesis.

Question 12

Where is the transverse pericardial sinus and what’s it’s use clinically? (Also, what’s the oblique sinus?)

Answer 12

The transverse pericardial sinus is the space behind the aorta and pulmonary trunk which is clamped when there’s a bypass machinery in use. (The oblique sinus is a dead end near the pulmonary veins at the posterior surface of the heart.)

Question 13

List 3 features of coronary arteries.

Answer 13

They’re end arteries, prone to a thermos and vital to supply well oxygenated blood to myocardium.

Question 14

Picture the heart and some of the coronary arteries and cardiac veins.

Answer 14

Check picture on images. Left and right coronary arteries, marginal arteries and circumflex branch round at the back. Anterior interventricular artery aka left anterior descending artery (widow maker). Posterior interventricular comes from right. Veins: anteriorly - small cardiac vein on left and great cardiac vein on right, posteriorly - all feed into coronary sinus, which drains into right atrium, as do the inferior and superior vena cava.

Question 15

What’s the difference between plasma and serum?

Answer 15

Serum is fluid collected from clotted blood, so serum = plasma - clotting factors (particularly fibrinogen).

Question 16

What is peripheral resistance?

Answer 16

Resistance of arteries to blood flow/totality of opposition to pumping heart.

Question 17

A marked increase in plasma viscosity can lead to an increase in whole blood viscosity and sludging at the peripheries (blood is more viscous when cool), what is the commonest cause?

Answer 17

Multiple myeloma - cancer of the bone marrow.

Question 18

What do the following terms mean and what can they all lead to? Polycythaemia, thrombocythaemia and leukaemia.

Answer 18

Polycythaemia is an increased number of red blood cells, thrombocythaemia is the same for platelets and leukaemia is the same for white blood cells. All three can lead to an increase in whole blood viscosity and sludging in the peripheries.

Question 19

Recently, C-reactive protein has been used as a measure for inflammation, why?

Answer 19

CRP is an acute phase proteins which increase in the blood in response to inflammation, producing a minor change in blood viscosity.

Question 20

Why does blood move from an area of high pressure to an area of low pressure.

Answer 20

It is a mixture of cells and plasma and considered a fluid.

Question 21

What is laminar flow of blood?

Answer 21

Blood flowing in stream lines with each layer remaining the same distance from the vessel walls. Blood in the centre has the highest velocity.

Question 22

Turbulent flow sees blood flowing in all directions and constantly mixing in a vessel, what 5 situations might cause it?

Answer 22

The rate of blood flow may be too great. Blood may pass through an obstructed vessel. It may make a sharp turn. It may pass over a rough surface. There may be an increased resistance to blood flow.

Question 23

What’s the difference between velocity and flow?

Answer 23

Velocity is the distance an object moves over time and is measured in distance/time, whereas flow is volume of liquid/gas moving over time and is measure in volume/time.

Question 24

What effect may stenosis have on flow?

Answer 24

Increase pressure (PSI - pounds per square inch) and so decrease flow, may lead to critical ischaemia.

Question 25

What’s the difference between a stenosis and an occlusion?

Answer 25

A stenosis is a narrowing whereas an occlusion is a blockage.

Question 26

How may a stenosis be noticed?

Answer 26

An abnormal sound through a stethoscope/murmur - bruit.

Thrill - buzz that you feel.

Question 27

In a pressure time graph of the descending aorta, what is the area under the curve and what can you tell from it? How else is it estimated? (MAP)

Answer 27

MAP - mean arterial pressure, estimated as diastolic pressure + 1/3 pulse pressure, so commonly 93mmHg. If it falls below 70mmHg, organ perfusion impaired.

Question 28

What are the anacrotic and dicrotic limbs on a graph?when does the dicrotic notch occur.

Answer 28

The anacrotic limb is the upstroke and the dicrotic limb is the line going down. The dicrotic notch occurs when the aortic valve shuts, at the end of systole.

Question 29

What is pulse pressure?

Answer 29

Peak systolic pressure - end diastolic pressure. Most commonly 120-80= 40mmHg. Determines how strong a pulse is.

Question 30

What is retrograde flow in arteries?

Answer 30

Blood moves backwards - greatest when peripheral resistance is high.

Question 31

What determines strength of pulse?

Answer 31

Force with with left ventricle pumps out blood into arterial system, creating shock wave.

Question 32

How is a weak pulse referred to and what can cause it?

Answer 32

A weak pulse is known as ‘thready’ and can occur if there is left ventricle failure, stenosis in the aorta or hypovolaemia (dehydration, blood loss).

Question 33

What is a strong pulse known as and what may cause it?

Answer 33

A strong pulse is ‘bounding’ and may be caused by bradycardia which widens pulse pressure by lowering diastolic pressure, as does low peripheral resistance e.g. from pregnancy, exercise or a hot bath.

Question 34

Explain Karotkoff sound phase 1.

Answer 34

External pressure>systolic pressure, so no flow and there is silence. Pulse obliteration.

Question 35

Explain what happens when diastolic pressure

Answer 35

There is partial flow and a sound is heard.

Question 36

Explain what happens at Karotkoff sound phase 5.

Answer 36

Sound disappears indicating that external pressure

Question 37

What can cause a falsely high BP reading?

Answer 37

The cuff being too small - it must cover at least 80% of the arm.

Question 38

What innervates the pericardium?

Answer 38

The phrenic nerve (on the way down to the diaphragm).