The Cardiac Cycle

Question 1

What are the 5 stages of the cardiac cycle?

Answer 1

1. ATRIAL SYSTOLE - atrial contraction forces small amount of additional blood into ventricles
2. ISOVOLUMIC VENTRICULAR CONTRACTION - first phase of ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves. Maximum blood volume in ventricles = end-diastolic volume (EDV)
3. VENTRICULAR EJECTION - as ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected
4. ISOVOLUMIC VENTRICULAR RELAXATION - as ventricles relax, pressure in ventricles fall. Blood flows back into cusps of semilunar valves and snaps them closed. Minimum blood volume in ventricles = end-systolic volume (ESV)
5. LATE DIASTOLE - both sets of chambers are relaxed and ventricles fill passively

Question 2

Heart sounds occur due to turbulence in blood flow caused by…

Answer 2

• 1st = closure of the AV (mitral and tricuspid) valves
• 2nd = closure of the semi-lunar (aortic and pulmonary) valves
• 3rd = rapid passive filling phase
• 4th = active filling phase
• These are normal
• Additional heart sounds are called murmurs (physiological or pathological)

Question 3

INTERPRET A PRESSURE VOLUME LOOP

Answer 3

USING THE ECG INTERPRETATION CASES STUDY (week 6)