The Cardiac Cycle

Question 1

list the 2 systolic phases of the cardiac cycle

Answer 1

1. isovolumic contraction
2. ejection

Question 2

list the 4 diastolic phases of the cardiac cycle

Answer 2

1. isovolumic relaxation
2. early, rapid ventricular filling
3. diastasis
4. atrial systole

Question 3

talk through the events occurring simultaneously in the left ventricle, left atrium, and aorta during isovolumic contraction (4)

Answer 3

1. mitral and aortic valves closed
2. ventricle takes time to build enough pressure to overcome reistance impose by aorta and systemic arterial tree (afterload)
3. ventricular volume is fixed (no place to go bc valves closed)
4. when ventricular pressure > aortic pressure, the aortic valve opens (cross over point around 80mmHg

Question 4

talk through the events occurring simultaneously in the left ventricle, left atrium, and aorta during ventricular ejection (8)

Answer 4

1. aortic valve open, mitral valve closed
2. ventricle and aorta become a common cavity
3. as blood moves forward into circulation, aortic and ventricular pressures rise together
4. rapid ejection: 70% of volume ejected in the first third of this phase
5. reduced ejection: the rest of the volume takes longer to eject because calcium is taken up by SR and vent pressure starts to decrease
6. ventricular volume decreases as blood exits the chamber
7. at end of ejection when ventricular pressure falls below aortic pressure, aortic valve closes (at 100mmHg) and gives second heart sound S2
8. through ventricular systole, atrial pressure and volume steadily increase, filling against the closed mitral valve

Question 5

talk through the events occurring simultaneously in the left ventricle, left atrium, and aorta during ventricular diastole/isovolumic relaxation

Answer 5

1. aortic and mitral valves closed
2. ventricular pressure rapidly decreases, but ventricular volume is fixed
3. when ventricular pressure < arterial pressure, mitral valve opens (around 10mmHg)

Question 6

talk through the events occurring simultaneously in the left ventricle, left atrium, and aorta during rapid ventricular filling

Answer 6

1. mitral valve opens (aortic valve closed)
2. ventricular volume begins to increase rapidly (accounts for majority of ventricular filling; ventricular suctions may contribute during exercise)
3. may be associated with a soft heart sound S3 (audible in normal horses and people, but only diseased dogs and cats)

Question 7

talk through the events occurring simultaneously in the left ventricle, left atrium, and aorta during diastasis

Answer 7

ventricular and arterial pressure begin to equalize, slowing ventricular filling (may even stop at slower heart rates)

Question 8

talk through the events occurring simultaneously in the left ventricle, left atrium, and aorta during atrial systole

Answer 8

1. atrial depolarization wave (P wave) arrives
2. arterial pressure rises, pushing the last bit of blood into the ventricle immediately before it contracts (primer function)
3. soft heart sound (S4) in pathologic states

Question 9

for each phase of the cardiac cycle, predict the position (open or closed) of the mitral and aortic valves

Answer 9

isovolumic contraction: aortic valve open, mitral valve closed
ejection: aortic valve open, mitral valve closed
isovolumic relaxation: aortic valve closed, mitral valve opens
rapid inflow: aortic valve closed, mitral valve opened
diastasis: aortic valve closed, mitral valve opened
atrial systole: aortic valve closed, mitral valve open

Question 10

understand the events associated with normal heart sounds

Answer 10

first heart sound (S1): LUB
-loudest and longest, closure of AV valves (mitral and tricuspid)

second heart sound (S2): DUB
-shorter and softer, closure of semilunar valves (aortic and pulmonic)

Question 11

be able to label/draw the Wigger’s diagram