Week 7- The Cardiac Cycle Flashcards
What are the 2 main phases of the cardiac cycle?
Diastole- ventricular relaxation (has 4 phases)
Systole- ventricular contraction (has 3 phases)
What is the stroke volume?
End diastolic volume - end systolic volume
What is the equation for ejection fraction?
Stroke volume divided by end diastolic volume
What happens to ejection fraction in those with breathlessness?
It is lower (around 30%)
What wave on an ECG signifies the start of atrial systole?
P wave
What could an abnormal 4th heart sound indicate?
Congestive heart failure, pulmonary embolism or tricuspid incompetence
What marks the start of ventricular depolarisation?
QRS complex
What is the isovolumetric contraction?
The interval between AV valves closing and semi lunar valves opening- contraction of ventricles with no change in volume
What causes the first heart sound?
The closure of the AV valves
What which phase of the cardiac cycle is there no heart sound?
Rapid ejection
State the phases of the cardiac cycle
Atrial systole Isovolumetric contraction Rapid ejection Reduced ejection Isovolumetric relaxation Rapid passive filling Reduced passive filling
What marks the start of rapid ejection?
Opening of aortic and pulmonary valves
What phase does reduced ejection mark the end of?
Systole
What happens during reduced ejection?
Aortic and pulmonary valves begin to close, blood flow from ventricles decreases and ventricular volume slowly decreases causing semilunar valves to close
What happens during isovolumetric relaxation?
AV valves remain shut until atrial pressure exceeds ventricular pressure
What causes the dichrotic notch?
Rebound pressure against aortic valve as distended aortic valve relaxes
What causes the 2nd heart sound?
Closure of the semilunar valves in isovolumetric relxation
When does rapid passive filling happen?
During the isoelectric flat between cardiac cycles
What is rapid passive filling?
When AV valves open blood in atria flows rapidly into ventricles
What may a 3rd heart sound indicate?
Turbulent ventricular filling due to hypertension or mitral incompetence
What is reduced passive filling known as?
Diastasis
What is atrial systole?
When the atria is almost full from passive filling due to pressure gradient, it contracts to top up blood volume in the ventricle
What is peak systole in the pulmonary artery?
25 mmHg
What is the difference in volume pumped out by the right side of the heart vs the left?
There is no difference in volume only in pressure generated
What is the pressure in the systemic circuit?
120/80 mmHg
Where is the preload encountered on the pressure volume loop?
During diastole when blood fills the ventricle and stretches the resting ventricular muscle
In the pressure volume loop what represents the afterload?
Blood pressure in the aorta and pulmonary artery
What does increased afterload do to stroke volume and why?
Decreases stroke volume because as afterload increases the amount of shortening that occours decreases
Define cardiac output
Contractile capability of the heart
What is the equation for cardiac output?
Heart rate x stroke volume
How is cardiac output measured?
Ejection fraction
How is cardiac output increased?
Sympathetic stimulation which can be hormonal (circulating adrenaline) or neural (noradrenaline from nerves)
What is cardiac output at rest?
4/5 L a minute
What is normal heart rate at rest?
60-100 bpm
