2.3. The heart cycle. Changes in pressure and volume during the cardiac cycle. Heart sounds. & 2.4A. Pump function of the heart

Question 1

I. Describe the heart sounds

Answer 1

1st heart sound:
- Closure of AV valves (tricuspid + bicuspid/mitral valves)
=> Loud, long, low frequency sound (noise)

2nd heart sound:
- Closure of semilunar valves (aortic + pulmonary valve)
=> Weak, short, high frequency sound (noise)

Question 2

II. Cardiac cycle
1. What is a cardiac cycle?

Answer 2

Refers to the sequence of mechanical and electrical events that repeats with every heartbeat. Can be divided into 2 phases: systole (contraction) and diastole (relaxation)

Question 3

II. Cardiac cycle
2. What is systole?

Answer 3

• Systole = ventricular contraction
• Time period between the beginnings of the 1st and 2nd heart sounds
• Electrical: beginning of Q wave to end of the T-wave

Question 4

II. Cardiac cycle
3. What is Diastole?

Answer 4

Diastole = ventricular relaxation
- Time period after 2nd heart sound till before the 1st heart sound

Question 5

II. Cardiac cycle
3. What is Electrical systole?

Answer 5

• Electrical systole = from the beginning of the Q-wave to the end of T-wave
• Duration of ventricular depolarization -> ventricular contraction

Question 6

II. Cardiac cycle
4. What is Atrial systole?

Answer 6

Atrial systole = occurs in late (ventricular) diastole
- Contraction of atrium = filling of ventricles
- Atrial systole is responsible for the small increases in atrial, ventricular, and venous pressure, as well as in ventricular volume

Question 7

II. Cardiac cycle -
5. What are the rules for construction of cardiac cycle?

Answer 7

1. Liquid is incompressible
   - Change of blood volume is negligible (volume will not change)
2. Direction of flow is determined by the pressure gradient
   - Blood flows from high pressure to low pressure
3. Opening / closing of valves is controlled by the direction of flow (passive opening)
   - Ex: AV valves open when atrial pressure > ventricular pressure
   - Ex: semilunar valves close when aortic pressure > ventricular pressure
4. No flow through closed valves

Question 8

III. Changes in pressure and volume during cardiac cycle
1. What are the 5 phases of cardiac cycle?

Answer 8

• Phase 1 – atrial depolarization/contract (diastole)
• Phase 2 – isovolumetric contraction (systole)
• Phase 3 – Ejection (systole -> diastole)
• Phase 4 – Isovolumetric relaxation (diastole)
• Phase 5 - filling

Question 9

III. Changes in pressure and volume during cardiac cycle
2. What happen during Phase 1 – atrial depolarization/contract (diastole)?

Answer 9

• Cardiac cycle is initiated with firing of the SA node that depolarizes the atria (P-wave)
• Atrial contraction causes atrial pressure to increase, forcing ventricular filling (ventricular volume↑)
• Both atrial and ventricular pressure increase simultaneously, until atrial contraction is over (atrial pressure decrease)
• Small decrease in aortic pressure = less blood remained to flow away from aorta

Question 10

III. Changes in pressure and volume during cardiac cycle
3. What happen during Phase 2 – isovolumetric contraction (systole)?

Answer 10

• Since ventricular pressure is larger than atrial pressure = AV valves close -> 1st heart sound (beginning of systole)
• Ventricle depolarization/contraction occurs -> increased ventricular pressure
• But since both AV and semilunar valves are closed = constant volume =
  ISOVOLUMETRIC CONTRACTION

Question 11

III. Changes in pressure and volume during cardiac cycle
4. What happen during phase 3 – Ejection (systole -> diastole)?

Answer 11

• As ventricular pressure increases, it will exceed the aortic pressure -> semilunar valves open
• Blood is ejected from ventricle to aorta
• Ventricular and aortic pressure increase a little bit, then decrease when ventricular repolarization occurs
• End of the ejection phase when aortic pressure is higher than ventricular pressure
  -> semilunar valves close
  => Closed semilunar valve: 2nd heart sound and the beginning of diastole (end of
  systole)

Question 12

III. Changes in pressure and volume during cardiac cycle
5. What happen during Phase 4 – Isovolumetric relaxation (diastole)?

Answer 12

• Ventricular pressure decreases rapidly, but no change in volume since all valves are
  closed -> ISOVOLUMETRIC RELAXATION
• Ventricular pressure is still higher than atrial pressure
• Atrial contraction increases slowly = atrial pressure increases
• When the atrial pressure exceeds the ventricular pressure -> AV valves open -> ventricular filling
• Incisure (dicrotic notch) represents the closure of the semilunar valve -> aortic pressure decreases slowly

=> Atria contract till the cardiac cycle repeats itself

Question 13

IV. Important values from the cardiac cycle - Pressure
1A. What is the value of Aortic pressure?

Answer 13

Aortic pressure ranges from 80 to 120 mmHg
- Semilunar valve opens at 80mmHg
- Semilunar valve closes at 100mmHg
- Max 120mmHg

Question 14

IV. Important values from the cardiac cycle
1B. What is the value of Ventricular pressure?

Answer 14

Ventricular pressure ranges from (barely above) 0 to 120 mmHg

Question 15

IV. Important values from the cardiac cycle
1C. What is the value of Atrial pressure?

Answer 15

Atrial pressure ranges from 4 to 8 mmHg:
- AV valve closes at 4 mmHg
- AV valve opens at 8 mmHg

Question 16

IV. Important values from the cardiac cycle - Blood volume
2A. What is the value of End diastolic volume (EDV)?

Answer 16

maximal volume = 140mL

Question 17

IV. Important values from the cardiac cycle - Blood volume
2B. What is the value of End systolic volume (ESV)?

Answer 17

minimal volume = 60mL

Question 18

IV. Important values from the cardiac cycle - Blood volume
2C. What is The value of Stroke Volume?

Answer 18

• Difference between EDV and ESC = stroke volume (SV) = 80mL
• SV = amount of blood transported to aorta during systole

Question 19

IV. Important values from the cardiac cycle
3. What are the definition and value of Ejection Fraction (EF)?

Answer 19

Ejection fraction (EF): what fraction of ventricular blood has been ejected
- EF = SV/EDV = blood ejected / blood in ventricle when filled
- 0,5 < EF < 0,75 -> more than 1⁄2, but less than 3⁄4 of volume should be ejected

Question 20

IV. Important values from the cardiac cycle
4A. What is the value of Systole time period?

Answer 20

0,27s ≈ 0,3s

Question 21

IV. Important values from the cardiac cycle
4B. What is the value of Diastole time period?

Answer 21

Diastole time period = 0,53s ≈ 0,5s

Question 22

IV. Important values from the cardiac cycle
4C. What is the length of cardiac cycle?

Answer 22

• Systole time period = 0,27s ≈ 0,3s
• Diastole time period = 0,53s ≈ 0,5s
  => Length of cardiac cycle = SYS + DIA = 0,8 seconds

Question 23

V. Left ventricular pressure-volume loop
1. What is Left ventricular pressure-volume loop?

Answer 23

Ventricular pressure loop describes one complete cycle of ventricular contraction, ejection, relaxation and refilling.

Question 24

V. Left ventricular pressure-volume loop
2. Describe the loop

Answer 24

Points:
- opening of mitral valve (diastole), ventricular filling -> ventricular volume ↑
- begins at a place where mitral valve opens (during diastole)
+) mitral valve closure occurs at low pressure
+) the ventricle fills from 50mL to 120mL
- now, isovolumetric contraction: pressure builds up from 10 to 90mmHg
- afterwards, the aortic valve opens and left ventricular pressure continues to rise
while volume decreases as it is ejected out into the aorta (around 70mL)
- as pressure begins to drop again and reaches 100mmHg, the aortic valve closes
- volume has now returned to the starting position of 50mL and so the heart
undergoes isovolumetric relaxation as the pressure declines back to its starting pressure of just above 0mmHg