The Cardiac Cycle - L4 Flashcards
What is the cardiac cycle?
All the events associated with the flow of blood through the heart during a single complete heartbeat
How long is the cardiac cycle is the heart rate is 65bpm?
approx 0.92 sec
What is 1 heart beat divided into?
2 Sequential phases: systole and diastole
What is systole?
Period of cardiac contraction and emptying
Often an implied time of ejection, despite period of isovolumetric contraction
What does systole vary on? What is it at 65bpm and 200bpm?
The length varies depending on what the heart rate: 0.3 sec @ 65bpm, 0.16 sec @ 200bpm
What happens at a higher heart rate to systole? What happens to calcium?
Myocardium contracts & repolarises faster at high HR (increased Calcium return to SR)
Systole is often an implied time of x?, despite x?
Often an implied time of ejection, despite period of isovolumetric contraction
What is diastole?
Period of cardiac relaxation
Often an implied time of refilling, despite period of isovolumetric relaxation
What does diastole vary with? @65bpm?@200bpm?
The length varies with varying heart rate
0.62sec @65bpm; 0.14sec @200bpm
Action of valves control?
Cardiac cycle
When do the AV valves open - the bicuspid/tricuspid valves??
open when pressure in atria is greater then those in the ventricles
when pressure gets greater in ventricles than in atria then the AV valves close
When do the semilunar valves open and close?
semilunar valves open when pressure in ventricles is greater then the pressure in the arteries and the semilunar valves close when the pressure in the arteries is greater then the pressure in the ventricles
Mechanical phases of cardiac cycle step:
- Late diastole: both sets of chambers are relaxed and
ventricles fill passively. - Atrial systole: atrial contraction forces a small amount of additional blood into ventricles.
- Isovolumic ventricular contraction: first phase of
ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves. 0.05 sec - Ventricular ejection: as ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves
open and blood is ejected. - Isovolumic ventricular relaxation: as ventricles relax, pressure in ventricles falls, blood flows back into cups of semilunar valves and snaps them closed.
What does cardiac cycle begin and end with?
Begins with a ventricular diastole and ends with a ventricular diastole
Heart sounds - what is S1:”lub”?
What is S2: “dup”?
S1 – “lub” (AV valve closure)
S2 – “dup” (semilunar valve closure)
With diastole it is often an implied time of x, despite x?
Often an implied time of refilling, despite period of isovolumetric relaxation
The sequence of events which may overlap are?
Atrial diastole -> ventricular diastole -> atrial systole -> ventricular systole
What is the action of the valves?
They open passively due to pressure gradients
EDV?
End diastolic volume = volume of blood in ventricle at end of diastole
130mL
ESV?
End systolic volume = volume of blood in ventricle at end of systole
70mL
SV?
Stroke volume = volume of blood ejected from ventricle in each cycle
SV = EDV-ESV
SV = 130-70 = 60mL in this case
What is the ejection fraction?
% EDV ejected with each stroke: ranges from 50-75%
What is ejection fraction useful for?
A good index of ventricular function
Wiggers’ Diagram main events: 6
- Atrial systole
- Isovolumic ventricular contraction
- Ventricular systole
- Early ventricular diastole
- Late ventricular systole
- Atrial systole again
1,2,3 make up QRS complex
4,5 cardiac cycle
cardiac cycle - one complete heartbeat
STEP 1 OF CARDIAC CYCLE
both atria and ventricles are filling passively: overlap
atria are passively filling from pulmonary veins from the lungs with oxygenated lungs and passively filling from the systemic return from the superior and inferior vena cava into right atria here, the AV valves are open as pressure is greater in atria then ventricles and blood fills ventricles
ventricles are filling passively
STEP 2 OF CARDIAC CYCLE: MECHANICAL PHASES
Atria have a systolic contraction to complete ventricular refilling
to force remaining blood in through valves and then the valves close
AV valves close
STEP 3
When AV valves close, just before we have the ventricular contraction where we have ejection of stroke volume that is when we have the period of the isovulimic ventricular contraction: AV closed here as pressure in ventricles is greater then what is in atria.
The ventricles are depolarising and they are getting ready to contract , the pressure is building, starting to contract but not forcefully enough to open semi lunar valves
All the valves are closed at this point - no blood entering or leaving
The volume remains the same but pressure is increasing, it is contracting.
Lasts 0.05 of a second
STEP 4 of cardiac cycle - mechanical phase
Systole has began, Ventricles are contracting, and now fully depolarised
Ventricular ejection occurs - ventricular pressure rises and exceeds the pressure in aorta and pulmonary artery, semi lunar valves open and blood leaves heart through these ventricles. The stroke volume occurs
Step 5 of cardiac cycle - mechanical phase?
Isovolumic ventricular relaxation
Ventricles has been ejected and now ventricles stop contracting and pressure reduces in ventricles and pressure within aorta and pulmonary arteries increases and causes closing of semi lunar valves. All the valves in heart are closed
When ventricles contract only 1/2 of blood is ejected, so some volume of blood left in ventricles
The volume is same but pressure is reducing
Ventricles are repolarising and getting ready to refill and begin the whole cycle again
- P wave?
- QRS?
- ST?
- T wave?
- TP?
- Atria depolarising, threshold has been reached
- Atria contracting and sending blood into ventricles and ventricles getting ready to contract and depolarises
- Ventricles are contracting and ejecting its contents
- Repolarisation of ventricle
- Ventricular diastolic, they are refilling
Isovolumic ventricular contraction happens at end of?
Isovolumic ventricular contraction happens at end atrial systole just before ventricular starts to do complete ventricle contraction
What is the dicrotic notch?
The end of systole and the beginning of diastole in these arteries.
EXAM Q - write about wiggers diagram, talk your way through each step: ECG, mechanical phase of cardiac cycle etc
