The cardiac cycle

Question 1

What are the key phases of the cardiac cycle in terms of pressure and volume changes?

Answer 1

Atrial systole – Atria contract, increasing atrial pressure and pushing blood into the ventricles.
Isovolumetric contraction – Ventricles begin to contract, increasing pressure but with no volume change as valves are closed.
Ventricular ejection – Ventricular pressure exceeds aortic/pulmonary artery pressure, causing semilunar valves to open and blood to be ejected.
Isovolumetric relaxation – Ventricles relax, pressure falls, but volume remains unchanged as valves are closed.
Ventricular filling – Atrial pressure exceeds ventricular pressure, AV valves open, and blood passively fills the ventricles.

Question 2

What is a pressure-volume (PV) loop, and what does it represent?

Answer 2

A PV loop is a graphical representation of the relationship between ventricular pressure and volume throughout the cardiac cycle. It illustrates stroke volume, contractility, afterload, and preload.

Question 3

What are the key phases of the pressure-volume loop?

Answer 3

Ventricular filling (low pressure, increasing volume).
Isovolumetric contraction (increasing pressure, constant volume).
Ventricular ejection (increasing pressure, then decreasing volume).
Isovolumetric relaxation (decreasing pressure, constant volume).

Question 4

What does an increase in preload do to the pressure-volume loop?

Answer 4

It shifts the loop rightward, increasing end-diastolic volume (EDV) and stroke volume.

Question 5

What does an increase in afterload do to the pressure-volume loop?

Answer 5

It shifts the loop upward and narrows it, increasing ventricular pressure but decreasing stroke volume.

Question 6

What does an increase in contractility do to the pressure-volume loop?

Answer 6

It shifts the loop leftward and upward, increasing stroke volume and decreasing end-systolic volume (ESV).

Question 7

What are the main heart sounds, and what causes them?

Answer 7

S1 (“lub”) – Closing of the mitral and tricuspid valves at the start of systole.
S2 (“dub”) – Closing of the aortic and pulmonary valves at the start of diastole.
S3 (abnormal in adults) – Rapid ventricular filling, often due to heart failure.
S4 (always abnormal) – Atrial contraction against a stiff ventricle, seen in hypertrophy.

Question 8

What is a phonocardiogram, and how does it relate to heart sounds?

Answer 8

A phonocardiogram is a graphical recording of heart sounds, displaying the timing and intensity of S1, S2, and any abnormal heart sounds or murmurs.