the cardiac cycle

Question 1

LV contraction

Answer 1

• Isovolumic contraction

* Maximal ejection

Question 2

LV relaxation

Answer 2

• Start of relaxation and reduced ejection
• Isovolumic relaxation
• Rapid LV filling and LV suction
• Slow LV filling (diastasis)
• Atrial booster

Question 3

Ventricular relaxation: Diastole

Answer 3

 LVp peaks then decreases
 Influence of phosphorylated phospholambdan, cytosolic calcium is taken up into the SR
 ‘phase of reduced ejection’
 Ao flow is maintained by aortic distensibility
 LVp < Aop, 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 (active diastolic relaxation), may also contribute to filling
 Diastasis (separation): LVp=Lap, filling temporarily stops
 filling is renewed when a contraction (booster), raises Lap creating a pressure gradient

Question 5

preload

Answer 5

is the load present before LV contraction has started

Question 6

afterload

Answer 6

is the load after the ventricle starts to contract

Question 7

Starling’s law of the heart

Answer 7

• Starling 1918: within physiologic limits, 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: is the difference between Lap and LV diastolic pressure
• The relationship reaches a plateau

Question 8

The force-length interactions & Starling’s law

Answer 8

• The force produced by the skeletal muscle declines when the sarcomere is less than the optimal length (actin’s projection from Z disc ‘1um’ x 2)
• In the cardiac sarcomere, at 80% of the optimal length, only 10% of the maximal force is produced

Question 9

‘All or none’

Answer 9

• The cardiac sarcomere must function near the upper limit of their maximal length (Lmax) = 22um
• The physiological LV volume changes are affected when the sarcomere lengthens from 85% of Lmax to Lmax
• Steep relationship: length-dependent activation

Question 10

Frank & iso-volumic contraction

Answer 10

• The heart can, during the cycle, increase and decrease the pressure even if the volume is fixed
• Increasing diastolic heart volume, leads to increased velocity and force of contraction (Frank 1895)
• This is the positive inotropic effect
• Ino: Fibre (Greek); tropus: move (Greek)

Question 11

Compliance

Answer 11

is the relationship between the change in stress and the resultant strain (dP/dV)

Question 12

Diastolic distensibility

Answer 12

the pressure required to fill the ventricle to the same diastolic volume

Question 13

Contractility (inotropic state)

Answer 13

the state of the heart which enables it to increase its contraction velocity, to achieve higher pressure (increases contractility). This is independent of load

Question 14

Elasticity

Answer 14

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