Cardiac cycle

Question 1

Cardiac cycle phases

Answer 1

LV contraction - isovolumic contraction, maximal ejection.
LV relaxation - start of relaxation and reduced ejection, isovolumic relaxation, rapid LV filling and LV suction, slow LV filling (diastasis), atrial booster.

Question 2

Ventricular contraction - systole

Answer 2

Wave of depolarisation arrives.
Opens the L-calcium tubule.
Ca2+ arrives at the contractile proteins.
LVp rises > LAp:
MV closes: M1 of the 1dt HS.
LVp rises (isovolumic contraction) > Aop.
AoV opens and ejection starts.

Question 3

Ventricular relaxation - diastole

Answer 3

LVp peaks then decreases.
Influence of phosphorylated phopsholambdan cytosolic calcium is taken up into the SR.
‘phase of reduced ejection’
Ao flow is maintained by aortic distensibility.
LVp<Ao p - Ao valve closes - A2 of the 2nd HS.
Isovolumic relaxation then MV opens.

Question 4

Ventricular filling

Answer 4

LVp<LAp, MV opens, rapid filling starts.
Ventricular suction may contribute to filling.
Diastasis: LVp=LAp, filling temporarily stops.
Filling is renewed when A contraction, raises LAp creating pressure gradient.

Question 5

Physiologic vs cardiologic systole

Answer 5

1) Isovolumic contraction
1) Maximal ejection
2) From M1 to A2.
2) Only part of isovolumic contraction.

Question 6

Physiologic vs cardiologic diastole

Answer 6

1) Reduced ejection
1) Isovolumic relaxation
3) Filling phases
1) A2 to M1 interval

Question 7

Preload vs afterload

Answer 7

Preload - is the load present before LV contraction has started.
Afterload - is the load after the ventricle starts to contract.

Question 8

Starling’s Law of the heart

Answer 8

The larger the volume of the heart - the greater the energy of its contraction and the amount of chemical change at each contraction.
LV filling pressure - difference between LAp and LV diastolic pressure.
The relationship reaches a plateau.

Question 9

The force-length interaction

Answer 9

The force produced by the skeletal muscle declines when the sarcomere is less than the optimal length.
In the cardiac sarcomere - at 80% optimal length - only 10% of the maximal force produced.

Question 10

‘All or none’

Answer 10

The cardiac sarcomere must function near the upper limit of their maximal length = 2.2 micrometres.
The physiologic LV volume changes are affected when the sarcomere lengthens from 85% to L max.

Question 11

Frank and isovolumic contraction

Answer 11

The heart can, during the cycle, increase and decrease the pressure even if the volume is fixed.
Increasing diastolic heart volume - increased velocity and force of contraction.
This is the positive inotropic effect.

Question 12

Compliance

Answer 12

The relationship between the change in stress and resultant strain.

Question 13

Diastolic distensibility

Answer 13

Pressure required to fill the ventricle to the same diastolic volume.