cardiac cycle Flashcards
how many phases is each heart beat split into
2
what is diastole and how long does it last
ventricular relaxation
lasts 2/3 of each heart beat
and is split into 4 distinct phases
what is systole and how long does it last
ventricular contraction
lasts approx 1/3 of each heart beat
split into 3 distinct phases
what is isovolumetric contraction
heart is exerting pressure on the end diastolic volume
what is end diastolic volume
volume present at maximum filling of the heart
what is end systolic volume
not all blood is ejected from the heart - some blood remains at the end of systole
what is stroke volume
the difference between end diastolic and end systolic
equation for stroke volume
end diastolic - end systolic
how do you calculate ejection fraction
stroke volume / end diastolic x 100
what is the normal range for ejection fraction
52-72%
what happens in bad heart failure
low ejection fraction > contractility of the ventricle is decreased
heart cannot sustain enough cardiac output for the needs of the body
used clinically to address degrees of failure of the heart
STEPS for what happens in atrial systole
contraction of the atria (already blood in the ventricles)
1) the P wave starts the process off
2) atria is stimulated by the pacemaker potential fired off by the SAN (excites atrial muscle cells and depolarisation excites atrial cells)
(P wave on ECG signifies start of atrial systole)
3) atria are already almost full from passive filling driven by pressure gradient
4) atria contract to “top up” volume of blood in ventricle
what is the 4th heart sound
abnormal, valve incompetence (leaky blood) - occurs with congestive heart failure, pulmonary embolism or tricuspid incompetence
STEPS for isovolumetric contraction
QRS complex - signifies depolarisation of ventricular muscle > activates the muscles (allows Ca influx into cells > calcium release from SR > Ca dumped into cytosol and activates myofilaments and produce contraction)
2) ventricles start to contract against closed valves (2 semi lunar and pulmonary and aortic valves are closed)
3) QRS complex marks the start of ventricular depolarisation (this is the interval between AV valves - tricuspid and bicuspid/mitral - closing and semilunar valves - pulmonary and aortic - opening)
4) ventricular volume doesn’t change - but build up in ventricular pressure
5) contraction of ventricles with no change in volume = isometric
1st heart sound (lub) due to closure of AV valves and associated vibrations
STEPS for rapid ejection
signifies ventricular pressure overcomes back pressure/diastolic blood pressure in the aorta and the blood pushes against aortic valve which opens and flows out of the ventricle > decreases volume
2) contraction has moved from isometric to isotonic (shortening of muscle fibres > efflux of blood from both ventricles)
3) opening of the aortic and pulmonary valves marks the start of this phase
4) as ventricles contract, pressure within them exceeds pressure in aorta and pulmonary arteries
5) semi lunar valves open, blood pumped out and the volumes of ventricles decrease (isotonic contraction)
no heart sounds