Cardiac cycle Flashcards
what is the cardiac cycle?
- all events that occur from beginning of 1 heartbeat to beginning of next heartbeat
- orderly depolarisation / repolarisation sequence triggers a recurring cardiac cycle of atrial & ventricular contractions and relaxations
what is diastole?
heart ventricles are relaxed & fill with blood (relaxation)
what is systole?
heart ventricles are contracting & pump blood into aorta (LV) and pulmonary artery (RV)
what is average heart rate and length of diastole/systole?
75 beats per min
- diastole = 0.5
- systole = 0.3
what are the 5 phases during cardiac cycle?
- passive filling
- atrial contraction
- isovolumetric ventricular contraction
- ventricular ejection phase
- isovolumetric ventricular relaxation
what is the passive filling stage of cardiac cycle?
- pressure of atria and ventricles close to 0
- AV valves open so venous return flows into ventricles
- aortic valve close, AV valve is open
- ventricles become 80% full by passive filling
what side has higher pressure?
left has much higher pressure than right
what is atrial contraction phase of cardiac cycle?
- P wave in ECG signals atrial depolarisation
- atria contracts between P wave and QRS
- after atrial contraction = left with end diastolic volume (usually about 65 mmHg)
what is isovolumetric ventricular contraction phase of cardiac cycle?
- ventricular contraction starts after QRS (signals ventricular depolarisation) in ECG
- ventricular pressure rises and when it exceeds atrial pressure, the AV valves shut
- closure of AV valves makes first sound -LUB which signals end of diastole and start of systole
- aortic valve is shut so no blood can enter or leave ventricle and tension rises around closed volume hence the name
what is the ventricular ejection phase of cardiac cycle?
- ventricular pressure exceeds aorta/pulmonary artery
- aortic/pulmonary artery valves open (silent)
- stroke volume ejected by each ventricle leaving behind end systolic volume
- T wave signals ventricular repolarization on ECG
- ventricles relax & pressure falls
- ventricular pressure falls below aortic/pulmonary artery pressure so valves shut and produces 2nd sound (DUB) = end of systole & start of diastole
- valve vibration makes the dicrotic notch in aortic pressure curve
how to calculate stroke volume?
end diastolic volume - end systolic volume
what is dicrotic notch caused by?
the valve vibration produces the dicrotic notch in aortic pressure curve
what is isovolumetric ventricular relaxation?
- closure of aortic/pulmonary artery valves - signals the start of isovolumetric relaxation
- ventricle is again a closed box, as AV valve is shut
- tension falls around a closed volume (isovolumetric relaxation)
- when ventricular pressure falls below the atrial pressure, AV valves open (silent event) and the heart starts a new cycle
what is the first sound caused by?
S1 = sounds like LUB and signals start of systole
- atrial & tricuspid valves closing
what is the second sound caused by?
S2 = sounds like DUB and signals end of systole and start of diastole
- by closure of aortic & pulmonary artery valves
