The cardiac cycle (27) Flashcards
What is diastole?
- ventricular relaxation: fills with blood
- lasts approx. 2/3 of each heartbeat
- split into 4 distinct phase
What is systole?
- ventricular contraction: generate pressure then eject blood into arteries
- lasts approx. 1/3 of each heartbeat
- split into 3 distinct phases
What is end diastolic volume?
ventricles filled completely
- 108 ml
What is end systolic volume?
ejected the blood that it is going to eject- some left
- 36 ml
What is the ejection fraction?
- describes contractility of the heart
- stroke volume / end diastolic volume x100
- should be around 67%
What are the 4 phases of diastole?
isovolumetric relaxation
rapid passive filling
slow passive filling
atrial systole
What causes the first heart sound (Lub)?
closing of AV valves
How does the pulmonary circuit pressure differ to the systemic circuit pressure?
- 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
What is a pressure volume loop and its landmarks?
- 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
What is cardiac output?
heart rate X stroke volume
What is contractility?
- measure of strength of contraction of heart (contractile capability)
- to measure: ejection fraction
- increased by sympathetic stimulation
How do you calculate stroke volume from end-diastolic and end-systolic volume?
end diastolic - end systolic = stroke volume
What occurs during atrial systole?
- 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
What occurs during isovolumetric contraction?
- 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
What occurs during rapid ejection?
- pressure in ventricles exceeds pressure in aorta
- blood expelled from ventricles, so ventricular volume decreases (isotonic contraction)
- SL valves open at start of phase
What occurs during reduced ejection?
- 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
What are the 3 phases of systole?
isovolumetric contraction
rapid ejection
reduced ejection
What occurs during isovolumetric relaxation?
- no change in ventricular volume, bc all valves closed
- ventricular muscles relax
- S2= SL valves shut
- ventricular pressure falls
- atrial pressure continues to rise
What occurs during rapid passive filling?
- 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
What occurs during reduced passive filling?
- diastasis
- ventricular volume increasing more slowly
- ventricles can fill considerably without atrial systole
What represents preload and afterload on pressure volume loops?
- preload= A, bc blood that has filled the ventricles during diastole determines the preload that stretches the resting ventricular muscle
- afterload= B
How would hardening of the aortic valve affect the normal PV loop?
greater back pressure-reduces flow and increases afterload (B is higher and dec. stroke volume)
How would acute blood loss affect the normal PV loop?
less blood back to heart–> reduced venous return–> dec. preload, so A shifted left, and dec. stroke volume
How would exercise affect the normal PV loop?
inc. sympathetic stimulation and HR–> inc. venous return, inc. contractility
- whole graph enlarged
