The Cardiac Cycle

Question 1

The cardiac cycle can be be categorised into the basic 3 events…

Answer 1

Luv contraction, relaxation and filling

Question 2

The events of the cardiac cycle goes as follows:

Answer 2

1. Isovolumic contraction
2. Maximal ejection
3. Start of relaxation and reduced ejection
4. Isovolumic relaxtion
5. Rapid filling of LV - due to suction of LV
6. Slow LV filling diastasis
7. Atrial booster

Question 3

What is ISO-volumic contraction?

Answer 3

Here you get ventricular depolarisation
Mitral valve and aortic valve closed
During contraction there is an increase in pressure, higher pressure in the ventricle will cause the aortic valve to open which leads to the period of maximum ejection.

Question 4

What is ventricular relaxation? Also now as diastole.

Answer 4

LV pressure decreases
Influence of phosphorylase phospholambdan leads to Ca2+ being taken up by sarcoplasmic reticulum causing muscle to relax
There is now a phase of reduced ejection
Aortic flow maintained by aortic distensibility
When the LV pressure becomes higher than the Aortic the aortic valve will close
= isovolumic relaxation

Question 5

Ventricular filling

Answer 5

Left ventricular pressure< LA pressure so mitral valve opens rapid filling of the ventricle starts ventricular suction also contributes to this

LV pressure will then = LA pressure and filling will stop

The filling is renewed when atrium contracts raising pressure greater than that in the ventricle.

Question 6

What is systole?

What is diastole?

Answer 6

Period between the 1st and 2nd heart sound — Closure of mitral then aortic valve.

When the heart is contracting

Diastole is the period between the closure of the aortic valve to the closure of the mitral.

When the heart is relaxing

Question 7

What is preload?

What is afterload?

Answer 7

Preload = the load present at the end of diastole before LV contraction has started

Afterload = load after the ventricle has contracted

Question 8

What is the pressure volume loop of the LV?

Answer 8

Reflects contractility in the end systolic pressure volume relationship while compliance is reflected at the end diastolic pressure volume relationship.

Question 9

Definitions:

Contractility?

Elasticity?

Compliance?

Diastolic distensibility?

Isometric contraction?

Isotonic contraction?

Answer 9

Contractility = the state of the heart which enables it to increase its contraction velocity to achieve higher pressure - independent of load.

Elasticity = myocardial ability to recover its normal shape after removal of systolic stress

Compliance = relationship between the change in stress and the resultant strain

Diastolic distensibility = pressure required to fill the ventricle to the Sam diastolic volume

Isometric contraction = contractions where the length of the muscle does no change

Isotonic contraction = contraction where the length of the muscle changes.