The Cardiac Cycle Flashcards
Describe atrial systole
Atrial contraction forces small amount of blood into ventricles
Describe the 2 stages of ventricular systole (including valves)
- Isometric ventricular contraction: first phase of ventricular contraction - pushes AV valves shut. But not enough pressure to open semilunar valves
- Ventricular ejection: as ventricular pressure rises and exceeds arterial pressure, the semilunar valves open and blood is ejected
Describe diastole
Atrial diastole: begins after atrial systole is complete
Isovolumic ventricular contraction: semilunar valves snapped shut as blood flows back into cusps and ventricular pressure falls leading to relaxation
Late diastole: both chambers are relaxes and ventricles fill passively
Describe the ventricular pressure variations during the cardiac cycle.
Increase in pressure from 0 to 120mmHg when mitral valve closes at 0s. Aortic valves opens about 0.1s and pressure falls to about 10mmHg by 0.5s and 0 by 0.8 seconds/
Describe the atrial pressure variations during the cardiac cycle.
Low pressure - up to 20mmHg.
A wave - increase in pressure due to atrial contraction before 0s
C wave: increase in pressure when mitral valve shuts at 0s putting pressure on the atrium
V wave starts to occur at about 0.7s: blood flows back into atrium and fills it leading to an increase in pressure
Describe the aortic pressure variations during the cardiac cycle.
Decrease in pressure from 100mmHg to about 75mmHg as mitral valve closes until aortic valve opens at 0.1s
Increase in pressure at about 0.2s then decrease to about 100mmHg and dicrotic notch where the filling phase is split into 2 - the aortic valve bounces shut and elastic energy bounces off the wall keeping pressure on and allowing pressure to fall slowly to about 75mmHg
Describe ventricular volume changes during the cardiac cycle
About 140ml (END DIASTOLIC PRESSURE) when mitral valve closes at 0s.
Falls during rapid ejection phase after aortic valve opens at 0.1s.
About 60ml (END SYSTOLIC PRESSURE) after aortic valve shuts.
Enters rapid filling phase at 0.3s when mitral valve opens again . Volume increases to about 130mls at 0.5s before entering a slower filling stage and then an active filling phase.
Why is ESV not 0?
Because the heart doesn’t need to push all blood out. The ESV is needed to make the heart contract more strongly during exercise
Why is the slower filling phase important?
Because important at a high heart rate vecayse t is important that most of the ventricle fills during the rapid 1/3 so that diastolic volume is not affected due to the shortening of the cardiac cycle and the shortening of the slow filling phase.
Describe how stroke volume and ejection fraction are calculated. Which is better at telling how healthy heart is working?
SV=EDV-ESV
EF = SV/EDV
EF is 2/3 in a healthy person
Describe heart sounds
S1 - closing of mitral valve
Sound between S1 and S2 - mitral/tricuspid regurgitation or aortic/pulmonary stenosis
S2 - closing of aortic valve
Sound between S2 and S1 - mitral stenosis or aortic regurgitation
Constant sound = septal defect
Describe the pressure volume loop
At LVV at 135ml, the EDV, the mital valve closes and the LV undergoes isovolumic contraction so pressure increases to about 100mmHg. The aortic valve opens when ventricular pressure exceeds aortic pressure and pressure rises to 120mmHg at 65ml (the ESV). The LV then undergoes isovolumic contraction and pressure falls to about 10mmHg. The mitral valve opens and blood flows in, increasing volume to 135ml (EDV) again
When does the aortic valve open?
When ventricular pressure exceeds aortic pressure
