Mechanical Properties of the Heart 2

Question 1

State the different phases of the cardiac cycle in order.

Answer 1

Atrial Systole
Isovolumic Contraction
Rapid Ejection
Reduced Ejection
Isovolumic Relaxation
Rapid Ventricular Filling 
Reduced Ventricular Filling

Question 2

What is the Ejection Fraction?

Answer 2

SV/EDV - the proportion of the blood in the heart that is pumped out in one contraction

Question 3

What ECG change is seen in atrial systole?

on

Answer 3

P wave - atrial depolarisati

Question 4

What abnormal heart sound could be heard during atrial systole and what could it be a result of?

Answer 4

S4 - this could be due to tricuspid incompetence, pulmonary embolism or congestive heart failure

Question 5

How does atrial pressure change during atrial contraction?

Answer 5

Atrial pressure shows a small increase - a wave

Question 6

Describe the pressure and volume changes that take place during isovolumic contraction.

Answer 6

The valves are all closed so there is no change in volume but the pressure increases dramatically.

Question 7

What heart sound will be heard during isovolumic contraction?

Answer 7

S1 - closing of the atrioventricular valves

Question 8

What ECG change is seen during isovolumic contraction?

Answer 8

QRS complex - ventricular depolarisation

Question 9

Describe what happens during rapid ejection.

Answer 9

The ventricular pressure exceeds the aortic and pulmonary pressures so the aortic and pulmonary valves open and blood rapidly flows out into the aorta and pulmonary artery.

Question 10

What causes the ‘c wave’ in atrial pressure during rapid ejection?

Answer 10

The ventricles contracting pushes the tricuspid valve inwards causing a slight increase in atrial pressure - c wave

Question 11

Describe the electrical activity and heart sound heard during rapid ejection.

Answer 11

There is no electrical activity - isoelectric line on ECG. No heart sounds are heard.

Question 12

Describe what happens during reduced ejection.

Answer 12

Marks the end of systole. Ventricular pressure begins to fall
T wave on the ECG due to the repolarisation of the ventricles. There are NO heart sounds because none of the valves are shutting.

Question 13

What is the dichrotic notch and when does it occur?

Answer 13

The dichrotic notch is caused by the elastic recoil of the aorta causing a small rise in aortic pressure once ventricular contraction has ended.

Question 14

What changes in pressure occur during isovolumic relaxation?

Answer 14

The atrial pressure increases due to the filling against closed valves - v wave. Volume of the ventricles does not change.

Question 15

What heart sound can be heard during isovolumic relaxation?

Answer 15

S2 - this is due to the shutting of the aortic and pulmonary valves

Question 16

What changes in volume and pressure take place during rapid ventricular filling?

Answer 16

There is a gradual increase in ventricular volume but ventricular pressure remains about the same. Atrial pressure decreases.

Question 17

What abnormal heart sound can be heard during rapid ventricular filling and what could it be a result of?

Answer 17

S3 - can be due to mitral incompetence or severe hypertension

Question 18

What happens during reduced ventricular filling?

Answer 18

Ventricular volume increases more slowly. This is also called diastasis. There are NO changes on ECG and NO heart sounds.

Question 19

What diagram can show all this information?

Answer 19

Wiggers diagram

Question 20

What is the difference between the pressures in the pulmonary circulation and in the systemic circulation?

Answer 20

The pressures in the pulmonary circulation are much lower (though the patterns of pressure changes are the same)

Question 21

State the average pressures of the systemic circulation and of the pulmonary circulation.

Answer 21

Systemic - 120/80

Pulmonary - 25/5

Question 22

What is used to measure preload on the left side of the heart?

Answer 22

PAWP - Pulmonary Artery Wedge Pressure

By measuring the pulmonary artery pressure you get an indirect measurement of the left atrial pressure

Question 23

What do points 1-4 on the pressure-volume loop indicate?

Answer 23

1 = End diastolic volume
2 = Isovolumic contraction (pressure has increased but volume hasn't)
3 = End systolic volume
4 = Isovolumic relaxation (volume doesn't change but pressure has decreased)

Question 24

Which feature of the pressure-volume loop indicates stroke volume?

Answer 24

Distance between point 2 and point 3

Question 25

Which points on the pressure-volume loop indicate preload and afterload?

Answer 25

Preload = point 1 (because it indicates the venous return to the heart and hence the stretch on the ventricular muscle) 
Afterload = point 2 (this is the end of isovolumic contraction when the pressure in the aorta and pulmonary artery (the afterload) is first experienced)

Question 26

Draw a diagram of the frank-starling relationship combined with a pressure-volume loop.

Answer 26

Starling’s Law = increased muscle fibres length causes increased ventricular contraction
The graph should be force against muscle fibre length (and pressure against volume)

Question 27

How does the pressure-volume loop change if the venous return to the heart is increased?

Answer 27

Points 1 and 2 move further to the right so the distance between 2 and 3 and hence the stroke volume, increases

Question 28

How does the pressure-volume loop change if the afterload is increased?

Answer 28

Points 3 and 4 move further to the right so the distance between 2 and 3, and hence the stroke volume, decreases. Also, point 2 and 3 move in a positive y direction so more pressure is required to open the aortic and pulmonary valves.

Question 29

What three factors can affect cardiac output?

Answer 29

Preload
Afterload
Contractility

Question 30

What is a simple measure of cardiac contractility?

Answer 30

Ejection Fraction

Question 31

How does the Frank-Starling Relationship change with increased contractility?

Answer 31

The gradient of the ESV line changes

Question 32

How does the pressure-volume loop change during exercise?

Answer 32

It becomes wider and the points move further out in all directions. EDV increases and ESV decreases (hence ejection fraction increases)