cardiac cycle Flashcards
what are the phases of heart beat?
diastole
systoles
what is diastole?
lasts 2/3 of each beat
ventricle relax
blood passively flows into the ventricles
(4 phases)
what is systole?
lasts 1/3 of each beat
ventricles contract
generate pressure then eject blood into arteries
(3 phases)
what is the end diastole volume?
maximum blood that can be held by a ventricle before contraction
120ml average
what is the end systolic volume?
volume of blood left after contraction
50ml average
what is the stroke volume?
end diastole volume - end systolic volume
average 70ml
what is ejection fraction?
100 x stroke volume/end diastolic volume
(58% average) 52-72% normal range
what is the cardiac cycle (all 7 steps)
and what phase do they belong to? (d-diastole, s-systole)
atrial systole d isovolumetric contraction s rapid ejection s slow ejection s isovolumetric relaxation d rapid passive filling d slow passive filling d
outline atrial systole step
P-wave is the start of atrial systole
Atria already almost full from passive filling driven by pressure gradient. Atria contract to ‘top-up’ the volume of blood in ventricle
4th heart sound – abnormal, occurs with congestive heart failure, pulmonary embolism or tricuspid incompetence
atrial pressure is higher than ventricle
outline isovolumetric contraction
QRS complex marks the start of ventricular depolarisation
This is the interval between AV valves (tricuspid & mitral) closing and semi-lunar valves (pulmonary & aortic) opening
Contraction of ventricles with no change in volume
1st heart sound (‘lub’) due to closure of AV valves and associated vibrations
pressure inside ventricle increases
outline the rapid ejection phase
Opening of the aortic & pulmonary valves mark the start of this phase
As ventricles contract pressure within them exceeds pressure in aorta and pulmonary arteries. Semilunar valves open, blood pumped out and the volumes of ventricles decrease.
No heart sounds for this phase
outline the reduced ejection phase
This phase marks the end of systole
Reduced pressure gradient means aortic & pulmonary valves begin to close
Blood flow from ventricles decreases and ventricular volume decreases more slowly
As pressures in ventricles fall below that in arteries, blood begins to flow back causing semilunar valves to close
Ventricular muscle cells repolarize producing T wave
outline the isovolumetric phase
The aortic & pulmonary valves shut, but the AV valves remain closed until ventricular pressure drops below atrial pressure.
Atrial pressure continues to rise. Dichrotic notch (green line) caused by rebound pressure against aortic valve as distended aortic wall relaxes.
2nd heart sound (‘dub’) due to closure of semilunar valves and associated vibrations
outline the rapid passive filling phase
Occurs during isoelectric (flat) ECG between cardiac cycles
Once AV valves open blood in the atria flows rapidly into the ventricles.
3rd heart sound – usually abnormal and may signify turbulent ventricular filling
Can be due to severe hypertension or mitral incompetence
outline the reduced passive filling phase
This phase can be called diastasis
Ventricular volume fills more slowly
The ventricles are able to fill considerably without the contraction of the atria.
