3.2 Cardiac Function

Question 1

List the four phases of diastole in order

Answer 1

• Isovolumetric relaxation
• Rapid inflow
• Diastasis (diastole-stasis)
• Atrial contraction (top up)

Question 2

List the three phases of systole in order

Answer 2

• Isovolumetric contraction
• Rapid ventricular ejection
• Reduced ventricular ejection

Question 3

Draw a left ventricular volume loop

Answer 3

https://www.adinstruments.com/sites/default/files/wysiwyg-resources/images/PV%20Loop%20parameter%20schematic%20Adam%20Goodwill.png

Question 4

What produces S1?

Answer 4

Atrioventricular valve closure

Question 5

What produces S2?

Answer 5

Semilunar valve closure

Question 6

When does the S3 sound occur (if it occurs)?

Answer 6

Ventricular filling

Question 7

What can cause an S4 heart sound to be heard?

Answer 7

Vibration of ventricular wall during end-diastolic atrial contraction

Question 8

Define preload

Answer 8

The tension applied to the left ventricle before it contracts; affected by end-diastolic volume

Question 9

What happens to cardiac contractility if preload becomes too high?

Answer 9

Cardiac muscle is stretched too far, and it begins to produce less contractile force

Question 10

Will maximum preload always result in highest stroke volume?

Answer 10

• No
• There is a point at which the contraction of ventricles will produce maximum force; beyond this, the force will decreased despite increased stretching of cardiac muscle

Question 11

List the three roles of atria in the cardiac cycle

Answer 11

• Collecting blood
• Passively filling ventricles
• Actively filling ventricles during atrial systole

Question 12

Which two factors can be used to quantify/conceptualise afterload?

Answer 12

• Aortic pressure
• Properties of arterial system

Question 13

What is the effect of increased/decreased preload on stroke volume?

Answer 13

Increased Preload: Increased Stroke Volume
Decreased Preload: Decreased Stroke Volume

Question 14

What is the effect of increased/decreased afterload on stroke volume?

Answer 14

Increased Afterload: Decreased Stroke Volume
Decreased Afterload: Decreased Stroke Volume

Question 15

Describe the location and mechanism of the baroreceptor reflex

Answer 15

• Location: carotid bodies and aortic arch
• Feed back information to the cardiovascular centre in the medulla
• Modulate autonomic innervation to regulate BP (incl. changes to heart and vascular system)

Question 16

Describe the function aortic stretch receptors in the heart in response to increased stroke volume

Answer 16

• Detect if stretch is too high (meaning ventricular filling has increased)
• Modulates increase in heart rate if necessary

Question 17

Describe the role of mechanoreceptors and metaboreceptors in skeletal muscle on heart function

Answer 17

• Feed back information regarding metabolic status of muscle to the cardiovascular centre, modulating stroke volume and heart rate (e.g. during exercise)

Question 18

List the main receptor types involved in extrinsic cardiovascular regulation

Answer 18

• Aortic stretch receptors in heart
• Baroreceptors in carotid bodies and aortic arch
• Metaboreceptors and mechanoreceptors in skeletal muscle

Question 19

Why might stroke volume decrease as HR increases?

Answer 19

Less time is available for diastolic filling, and so stroke volume decreases

Question 20

Describe the cardiovascular response to exercise. What happens to stroke volume as heart rate nears its maximum?

Answer 20

1. Central command assists with a rapid
   early rise in HR.
2. Muscle pump ↑ venous return, which
   ↑ central venous pressure, thus
   engaging the Starling mechanism.
3. Matching of HR to the metabolic
   demand achieved by afferent
   feedback via muscle mechano- and
   metaboreceptors.
4. At higher HR, stroke volume plateaus
   and falls due to limited diastolic filling
   time.
5. At peak exercise, cardiac output
   plateaus as HR reaches its upper
   limit.

Question 21

Which two factors can be used to quantify/conceptualise afterload?

Answer 21

• Aortic pressure
• Properties of arterial system