Cardiac Cycle

Question 1

what is the cardiac cycle?

Answer 1

Sequence of electrical and mechanical events in a complete heart beat

Question 2

study slide 6 of Nov 23

Answer 2

ya

Question 3

main events for complete cardiac cycle

Answer 3

first event: ventricular systole; second event: ventricular diastole

Question 4

describe ventricular systole

Answer 4

2 periods: Isovolumic ventricular contraction and Ventricular ejection

Question 5

describe Isovolumic ventricular contraction

Answer 5

No change in ventricular volume  
Steady and rapid increase in
ventricular pressure  
All the valves are closed;
coincides with peak of R wave; occurs between the closure of the AV valves and the opening of the semilunar valves; increase atrial pressure observed (from the closure of AV valve); first sound heard--caused by closure of AV valves

Question 6

what is the volume of blood left in the left ventricle after ventricular filling called?

Answer 6

end-diastolic volume/pre-load

Question 7

describe ventricular ejection

Answer 7

Begins with the opening of the semilunar valves
(AV valves are now closed)
  Further sub-divided into 2 phases:
i) Rapid ejection phase
ii) Reduced ejection phase

Question 8

describe rapid ejection phase

Answer 8

starts with the initial opening of semilunar; Sharp increase in the ventricular and aortic pressurebut with ventricular pressure slightly above the aortic pressure
There is a sharp decrease in ventricular volume
The sudden drop in atrial pressure is caused by the descent of the base of the heart and the stretch of the atria during ventricular contraction
Ends when:
left ventricular pressure is at its peak @ this
particular cardiac cycle
ventricular pressure = aortic pressure
–>Arterial systolic pressure
It is approximately 1/3 of the whole ejection phase in duration

Question 9

describe reduced ejection phase

Answer 9

Both the ventricular and aortic pressures are starting to decrease
Continuation of blood flow from ventricle to aorta
–> with ventricular pressure slightly less than
aortic pressure
Decline in aortic pressure is due to the runoff of blood from aorta to the systemic circulation
This phase coincides with the onset of T-wave of the ECG
This period occupies approximately 2/3 of the whole ejection period in duration

Question 10

what composes ventricular diastole

Answer 10

isovolumic ventricular relaxation; ventricular filling

Question 11

what is isovolumic ventricular relaxation

Answer 11

period while the ventricle is relaxing;
No change in ventricular volume during this
but with a steady decrease in ventricular pressure
semilunar and AV valves are closed
Period between closure of semilunar valves and opening of the AV valves
Rapid decrease in ventricular pressure
There is a sudden increase in aortic pressure
(dicrotic notch)
due to the closure of aortic valve
Onset of second heart sound
–with a higher pitched sound
–described as a “dupp” sound
–associated with the closure of semilunar valves

Question 12

what is the volume of blood left i nthe ventricle during isovolumic ventricular relaxation?

Answer 12

end-systolic volume

Question 13

what is stroke volume?

Answer 13

as the amount of blood ejected by the heart per beat; SV = EDV – ESV

Question 14

what is ventricular filling?

Answer 14

divided into

i) rapid filling phase
ii) reduced filling phase

Question 15

describe rapid filling phase

Answer 15

Majority of ventricular filling occurs in this phase (~ 70%)
By passive filling
i.e.) no atrial contraction
3rd heart sound (very faint) can be heard associated with the turbulent blood flow
during the ventricular filling
The initial drop in atrial pressure is due to the opening of the AV valve

Question 16

describe reduced filling phase

Answer 16

Atrial contraction occurs in this phase
Which coincides with:
a) The mid-way of P-wave of the ECG
b) A sudden increase in the atrial pressure
c) An additional increase in ventricular volume (~ 30%)
This phase also known as the active ventricular filling phase
This phase ends with the closure of the AV-valve
i.e.) The beginning of the isovolumic ventricular contraction