Cardiac cycle pt.1. Flashcards
What are the names of the stages of the cardiac cycle?
late diastole
atrial systole
isovolumic ventricular contraction
ventricular ejection
isovolumic ventricular relaxation
What happens in late diastole?
both chambers of the heart are relaxed and the ventricles are filling passively with blood
heart going to be full of blood and then when the pacemaker reaches threshold potential- wave of depolarisation is going to spread throughout the atria leading to atrial contraction
What happens in atrial contraction?
squeeze last bit of blood from atria into ventricles.
Here the pressure in the atria exceeds the pressure in the ventricles and that causes the mitral and tricuspid valves to open
What happens in isovolumic ventricular contraction?
ventricles are going to depolarise and contract.
When they contract they push the mitral and tricuspid valves closed.
Entry and exit valves to ventricles are closed
as ventricular pressure rises and exceeds pressure in the aorta and pulmonary trunk
causes aortic and pulmonary valves to open
What happens in ventricular ejection?
blood pumped out of ventricles into aorta and pulmonary trunk
ventricles begin to relax and pressure in ventricles drops and when pressure in ventricles drops below the pressure in aorta and pulmonary trunk - the aortic and pulmonary valves close.
What happens in isovolumic ventricular relaxation?
second phase
blood can’t get in or out of ventricles and volume in ventricles stays constant.
Blood will fill into atria and as they fill with blood- the pressure gradually increase until exceeds pressure in ventricles. This pushes mitral and tricuspid valves open and blood flows from atria into ventricles.
How is the cycle distributed into systole and diastole filling stages?
1/3 - systole
2/3- diastole
What is heart beat of someone with cardiac cycle of 0.8s?
60/0.8= 75 bpm
What happens to diastole at higher heart rates?
diastole decreases and so it becomes a smaller proportion of the total cardiac cycle
Describe pressure changes in left ventricle?
at time 0s - the ventricle is beginning to contract
when left ventricle contracts- the pressure in left ventricle very rapidly increases.
When pressure in left ventricle exceeds pressure in left atrium , causes mitral valve to close.
Then have phase where both the mitral and aorta valve is closed and blood can’t get out of ventricle.
Volume of blood plateaus at 140ml
When it exceeds pressure in the aorta , that pushes the aortic valve open and blood is ejected from left ventricle into aorta.
Pressure will continue to increase and it reaches a peak of about 120mmHg.
Muscle has to relax and therefore pressure will then decrease and when pressure in LV falls below pressure in aorta , aortic valve will shut.
Then have isometric relaxation phase and entry and exit valves to LV are closed- so both aortic valve is closed and mitral valve is closed.
Plateau in volume of blood in LV at 60ml.
When pressure in LV falls below pressure of LA causes mitral valve to open and blood from atrium flows into ventricle.
After this pressure in LV is low and constant and there is a little blip where last bit of blood from atria goes into ventricles (small increase in pressure)
Why can’t contraction of muscle continue?
intracellular calcium concentrations decrease , less crossbridging and get relaxation of muscle.
Describe the pressure in aorta during cardiac cycle?
when the pressure in left ventricle exceeds the pressure in aorta that pushes aortic valve open and blood flows into aorta.
Aorta pressure will closely match pressure in left ventricle as they’re linked and pressure in aorta peaks at 120mmHg. (systolic pressure)
Until aortic valve closes and there is a dicrotic notch (elastic energy in walls of aorta can push some blood still through) .
Pressure in aorta decreases very slowly due to elastic properties. Pressure in aorta is much more maintained.
Minimum pressure in aorta during diastole is 80mmHg.
How do you work out pulse pressure?
120-80= 40mmHg
What is mean arterial pressure?
one third way between diastolic and systolic
Describe pressure in left atrium during cardiac cycle?
three increases in the pressure in the left atrium known as waves
a wave - caused by atrial contraction
c wave - mitral valve bulges into atrium and causes increase in pressure
when aortic valve opens and blood flows from LV into aorta - pressure on LA decreased
v wave- even during systole , have blood returning from lungs to LA. Atrium has low volume and so when blood flows into it - pressure will increase and increase.
When pressure in LA exceeds pressure in LV, mitral valve will open and blood flows from LA into LV. Decrease in pressure
Describe volume in the cardiac cycle?
the maximum volume at end of diastole- end diastolic vol (EDV) (140ml)
minimum volume at end of systole- end systolic volume (60ml)
What is stroke volume?
difference between EDV and ESV
What is ejection fraction?
SV/EDV
what percentage of blood in ventricle is pumped out with each contraction
Isometric contraction phase volume?
volume in left ventricle remains constant - plateaus at 140
Volume during rapid ejection phase?
volume decreases very rapidly
Volume during slower ejection phase?
volume decreases from previous phase but slower about 60ml
What is the rapid filling phase?
after isometric relaxation phase where aortic and mitral valves are closed again- pressure in LA exceeds pressure in LV and mitral valve opens and blood flows into LV.
THEN HAVE SLOWER FILLING PHASE
How do pressures in RHS of heart compare to LHS?
fifth of LHS as LHS pumps to systemic circulation
