The cardiac cycle (27)

Question 1

What is diastole?

Answer 1

• ventricular relaxation: fills with blood
• lasts approx. 2/3 of each heartbeat
• split into 4 distinct phase

Question 2

What is systole?

Answer 2

• ventricular contraction: generate pressure then eject blood into arteries
• lasts approx. 1/3 of each heartbeat
• split into 3 distinct phases

Question 3

What is end diastolic volume?

Answer 3

ventricles filled completely

- 108 ml

Question 4

What is end systolic volume?

Answer 4

ejected the blood that it is going to eject- some left

- 36 ml

Question 5

What is the ejection fraction?

Answer 5

• describes contractility of the heart
• stroke volume / end diastolic volume x100
• should be around 67%

Question 6

What are the 4 phases of diastole?

Answer 6

isovolumetric relaxation
rapid passive filling
slow passive filling
atrial systole

Question 7

What causes the first heart sound (Lub)?

Answer 7

closing of AV valves

Question 8

How does the pulmonary circuit pressure differ to the systemic circuit pressure?

Answer 8

• patterns of pressure changes are essentially identical
• however, pressures in the pulmonary circuit (RHS) are much lower
• but right ventricle ejects same volume of blood as left

Question 9

What is a pressure volume loop and its landmarks?

Answer 9

• point A= end-diastolic point
• A–>B= isovolumetric contraction
• B= diastolic blood pressure (aorta)
• B–>C= ejection phase (its peak is systolic blood pressure)
• C= S2, end systolic volume
• C–>D= isovolumetric relaxation
• D–>A= passive filling and atrial contraction

Question 10

What is cardiac output?

Answer 10

heart rate X stroke volume

Question 11

What is contractility?

Answer 11

• measure of strength of contraction of heart (contractile capability)
• to measure: ejection fraction
• increased by sympathetic stimulation

Question 12

How do you calculate stroke volume from end-diastolic and end-systolic volume?

Answer 12

end diastolic - end systolic = stroke volume

Question 13

What occurs during atrial systole?

Answer 13

• ventricles filling w/ blood
• SAN activation–> wave of depolarisation- P wave on ECG
• atria contract and top up volume in ventricle
• S4= abnormal heart sound, due to tricuspid incompetence, pulmonary embolism

Question 14

What occurs during isovolumetric contraction?

Answer 14

• wave of depolarisation down septum to ventricles–> QRS complex
• ventricles contract (isometrically), pressure increases but volume doesn’t change
• all valves closed
• S1= closing of AV valves at beginning of this period

Question 15

What occurs during rapid ejection?

Answer 15

• pressure in ventricles exceeds pressure in aorta
• blood expelled from ventricles, so ventricular volume decreases (isotonic contraction)
• SL valves open at start of phase

Question 16

What occurs during reduced ejection?

Answer 16

• blood outflow occurs do to inertial energy, but ventricular volume decreases more slowly
• ventricles repolarise–> T wave
• end of systole
• as ventricular pressure falls below arterial, blood begins to flow back, so SL valves begin to close

Question 17

What are the 3 phases of systole?

Answer 17

isovolumetric contraction
rapid ejection
reduced ejection

Question 18

What occurs during isovolumetric relaxation?

Answer 18

• no change in ventricular volume, bc all valves closed
• ventricular muscles relax
• S2= SL valves shut
• ventricular pressure falls
• atrial pressure continues to rise

Question 19

What occurs during rapid passive filling?

Answer 19

• AV valves open
• blood passively fills ventricles
• flat ECG (isoelectric) between cardiac cycles
• S3= abnormal, signifies turbulent ventricular filling due to hypertension or mitral incompetence

Question 20

What occurs during reduced passive filling?

Answer 20

• diastasis
• ventricular volume increasing more slowly
• ventricles can fill considerably without atrial systole

Question 21

What represents preload and afterload on pressure volume loops?

Answer 21

• preload= A, bc blood that has filled the ventricles during diastole determines the preload that stretches the resting ventricular muscle
• afterload= B

Question 22

How would hardening of the aortic valve affect the normal PV loop?

Answer 22

greater back pressure-reduces flow and increases afterload (B is higher and dec. stroke volume)

Question 23

How would acute blood loss affect the normal PV loop?

Answer 23

less blood back to heart–> reduced venous return–> dec. preload, so A shifted left, and dec. stroke volume

Question 24

How would exercise affect the normal PV loop?

Answer 24

inc. sympathetic stimulation and HR–> inc. venous return, inc. contractility
- whole graph enlarged