The cardiac cycle Flashcards
What are the stages of the cardiac cycle?
Late diastole
Atrial Systole
Isovolumic ventricular contraction
Ventricular ejection
Isovolumic ventricular relaxation
What happens during late diastole?
Both chambers of heart are relaxed and ventricles are filling passively with blood
When pacemaker reaches threshold potential = wave of depolarisation
What happens during atrial systole?
Wave of depolarisation spreads form atria to ventricle
Atrial contraction forces a small amount of additional blood into ventricles
What happens during isovolumic ventricular contraction?
Ventricles depolarise and contract pushing mitral and tricuspid valves closed
First phase of ventricular contraction pushes AV valves closed
Does not create enough pressure to open semilunar valves
Maximum blood volume in ventricles = End-diastolic volume (EDV)
Increasing pressure due to increasing volume of blood with nowhere to go
What happens in ventricular ejection?
Ventricular pressure rises and exceeds pressure in the arteries
Semilunar valves open and blood is ejected
What happens in isovolumic ventricular relaxation?
As ventricles relax, pressure in ventricles falls
Blood flows back into cusps of semilunar valves and snaps them closed
Minimum blood volume in ventricles = End-systolic volume (ESV)
Blood flows back into atria increasing pressure in them until it exceeds pressure in ventricles pushing mitral and tricuspid valves open and blood flows into ventricles.
What is diastole?
Filling phase
What is systole?
Ejection phase
What proportion of the cardiac cycle is systole?
1/3 = 0.2s
What proportion of the cardiac cycle is diastole?
2/3 = 0.6s
How long does a whole cardiac cycle take?
0.8s = 75bpm
What happens to diastole at higher HRs?
Diastole decreases (becomes smaller proportion of cycle)
What happens to the LV at the start of the cardiac cycle?
Pressure rapidly increases in LV
When it exceeds pressure in the LA the mitral valve closes
With mitral and aortic valves closed, volume of blood in LV plateaus
What happens after rapid filling of the ventricle?
Isometric contraction phase
- Pressure continues to increase rapidly and when it exceeds pressure in the aorta the valve opens and blood is ejected from LV into the aorta
Why cant this high pressure be maintained for long?
Intracellular calcium concentration decreases
Less cross bridging and thus relaxation of the muscle
= Pressure decrease
What causes aortic valve to shut?
When pressure in the LV falls below aortic pressure
What happens int he isometric relaxation phase?
Entry and exit valves to the LV are closed
Blood volume plateaus as not moving.
What happens after isometric relaxation phase?
Pressure in LV falls below pressure in LA
Causes mitral valve to open and blood to flow from LA into LV.
Pressure in LV is very low and remains constant
What happens to the aorta when pressure in the LV exceeds aortic pressure?
Aortic valve opens
Blood is ejected from LV into aorta
Pressure in aorta matches pressure in LV closely until the aortic valve closes
What does aortic pressure peak at?
120 mmHg = systolic pressure
What is the dicrotic notch and what is it due to?
A blip splitting the falling phase in two
Due to the elastic properties of the aorta
- During systole walls of aorta expands
- During diastole blood elastic energy stored in walls push against column of blood and keep it flowing through
Because when aortic valve closes = elastic recoil
How quickly does pressure fall in the LV compared to the aorta?
LV = falls rapidly
Aorta = slowly due to elastic properties
- The elastic walls maintain pressure in the artery
What is the minimum pressure in the aorta during diastole?
80 mmHg
What is pulse pressure?
Difference between diastolic and systolic pressure
What is mean arterial pressure?
1/3 between diastolic and systolic pressures
What are the 3 waves in pressure in the left atrium?
A wave
C wave
V wave
What happens during A wave in the left atrium?
Atrial contraction
What happens during C wave in the left atrium?
When mitral valve closes it bulges into left atrium increasing LA pressure
Aortic valve opens and pressure in LV falls so pressure on valve falls and C wave falls
What happens during V wave in the left atrium?
Long and slow
Pressure in atrium gradually increases as blood flows in (returning from lungs)
Pressure LA > pressure in LV mitral valve opens and blood flows from LA to LV
- Decrease in pressure
What does EDV mean?
End diastolic volume
- volume at the end of diastole
What does ESV mean?
End systolic volume
- Minimum volume at end of systole (not zero as wont pump all blood out)
What is stroke volume?
ESV - EDV
The amount of blood ejected out of the ventricle into the aorta
What is the ejection fraction?
Stroke volume divided EDV
% of blood in ventricle pumped out with each contraction
How does the process of contraction in the left heart compare to the right?
Exactly the same, except pressure in the right is 1/5th of pressure on the left
How do heart sounds occur?
Turbulence in blood flow caused by closure of heart valves
What causes the 1st heart sound?
Closure of the AV (mitral and tricuspid) valves
What causes the 2nd heart sound?
Closure of the semi-lunar (aortic and pulmonary) valves
What causes the 3rd heart sound?
Rapid passive filling phase
What causes the 4th heart sound?
Active filling phase
What sounds should always be heard and what are less common?
Can always hear 1st and 2nd
3rd and 4th not always heard
Who are physiological/innocent murmurs more common in?
Infants/children and pregnant women
What is the pattern of heart sounds with systole and diastole?
Lub systole dub diastole, lub systole dub diastole etc.
What are some causes of pathological murmurs? (2)
- Valve that should be open is narrowed or stenosed causing turbulent blood flow
- Valve that should be closed is leaky and allows blood to regurgitate back through it
What do you call the two types of murmur?
Stenosis
Regurgitation
What could a systolic murmur sound like?
lub st dub, lub st dub etc.
What is stenosis?
Narrowing of a valve causing turbulent blood flow
What is regurgitation?
Leaky valve allows blood to regurgitate back through it
What can cause a systolic murmur?
Stenosis/narrowing of aortic/pulmonary valves causing turbulence.
Regurgitation of blood through mitral or tricuspid valves.
What could a diastolic murmur sound like?
lub dub st, lub dub st etc.
What are some causes of diastolic murmurs?
Stenosis of mitral and tricuspid valves
Regurgitation of aortic or pulmonary valves
What is a continuous murmur?
Heard throughout systole and diastole
What could cause a continuous murmur?
Patent ductus arteriosus
What is a patent ductus arteriosus?
When the ductus arteriosus (a small vessel joining the pulmonary trunk to the aorta during foetal stage) doesn’t close after birth.
Pressure is higher in aorta than pulmonary trunk so some blood will flow from aorta to pulmonary trunk causing turbulent blood flow and a continuous murmur
