The Cardiac Cycle

Question 1

3 basic evens of the cardiac cycle

Answer 1

• LV contraction,
• LV relaxation,
• LV filling.

Question 2

The cardiac cycle phases- LV contraction

Answer 2

• Isovolumic contraction ( b )
• Maximal ejection ( c )

Question 3

The cardiac cycle phases- LV relaxation

Answer 3

• Start of relaxation and reduced ejection ( d )
• Isovolumic relaxation ( e )
• Rapid LV filling and LV suction ( f )
• Slow LV filling (diastasis) ( g )
• Atrial booster ( a ).

Question 4

Ventricular contraction: Systole

Answer 4

Wave of depolarisation arrives,
Opens the L-calcium tubule, {ECG: Peak of R},
Ca2+ arrive at the contractile proteins,
LVp rises > LAp:
MV closes: M1 of the 1st HS, first heart sound
LVp rises (isovolumic contraction) > Aop,
AoV opens and Ejection starts.

Question 5

Ventricular relaxation: Diastole

Answer 5

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 < Ao p, Ao. valve closes, A2 of the 2nd HS.
“isovolumic relaxation”, then “MV opens”.

Question 6

Ventricular filling

Answer 6

LVp < LAp, MV opens, Rapid (E) filling starts.
Ventricular suction (active diastolic relaxation), may also contribute to E filling (esp. ex. ?S3).
Diastasis (separation): LVp=LAp, filling temporarily stops.
Filling is renewed when A contraction (booster), raises LAp creating a pressure gradient.(path, S4)

Question 7

Physiologic systole

Answer 7

Isovolumic contraction

Maximal ejection

Question 8

Cardiologic systole

Answer 8

From M1 to A2

Only part of isovolumic contraction (includes maximal and reduced ejection phases)

Question 9

Physiologic diastole

Answer 9

Reduced ejection

Isovolumic relaxation

Filling phases

Question 10

Cardiologic Diastole

Answer 10

A2 to M1 interval (filling phases included)

Question 11

Preload

Answer 11

is the load present before LV contraction has started

Volume of blood in the LV which streches the cardiac myocytes before LV contraction. Load present before LV contraction has started (EDV).

Question 12

Afterload

Answer 12

is the load after the ventricle starts to contract

Pressure the LV must overcome to eject blood during contraction

Question 13

Starling’s Law of the heart

Answer 13

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
The more the ventricles fill, the harder they contract
Higher end diastolic volume= myocytes stretch= increase in strength of contraction= increase in cardiac output

•LV filling pressure: is the difference between LAp and LV diastolic pressure

•The relationship reaches a plateau

Question 14

The Force-Length Interaction & Starling’s law

Answer 14

The force produced by the skeletal muscle declines when the sarcomere is less than the optimal length (Actin’s projection from Z disc “1micrometre” X 2).

In the cardiac sarcomere, at 80% of the optimal length, only 10% of the maximal force is produced

Question 15

All or none principal

Answer 15

The cardiac sarcomere must function near the upper limit of their maximal length (LMAX) = 2.2 micrometer.

The physiologic LV volume changes are affected when the sarcomere lengthens from 85% of LMAX to LMAX

Steep relationship: length-dependent activation.

Question 16

Frank and Isovolumic contraction

Answer 16

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 17

Contractility (inotropic state)

Answer 17

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

The pressure-volume loop reflects contractility in the end-systolic pressure volume relationship, while compliance is reflected at the end diastolic pressure volume relationship

Force of contraction and the change in fibre length - how hard the heart pumps.
When muscle contracts myofibrils stay the same length but the sarcomere shortens - force of heart contraction that is independent of sarcomere length

Question 18

Elasticity

Answer 18

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

Question 19

Compliance

Answer 19

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

How easily the heart chamber expands when filled with blood volume

Question 20

Diastolic distensibility

Answer 20

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

Question 21

Isometric vs. Isotonic contraction

Answer 21

Iso = the same (Greek),
Metric = length (Greek),
Tonic = contractile force (Greek),

The force-velocity curve may be a combination of initial isometric conditions followed by isotonic contraction.

The isometric conditions can be found during isovolumic contraction, isotonic contraction is totally impossible in the heart, given the constantly changing load.

Question 22

Total Peripheral Resistance

Answer 22

Total resistance to flow in systemic blood vessels from beginning of aorta to vena cava - arterioles provide the most resistance

Question 23

Stroke volume

Answer 23

Volume of blood ejected from each ventricle during systole
SV = end diastolic volume - end systolic volume

Question 24

Cardiac cycle is 72 bpm

Answer 24

0.3 secs- systole

0.5 secs- diastole

Systole – Ventricular Contraction and blood ejection
Diastole – Ventricular relaxing and blood filling.
Unless clearly states atrial systole etc

Question 25

Basic 3 events

Answer 25

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 (systole)

LV filling

Question 26

Ventricular contraction- Systole

Answer 26

1) Wave of depolarisation arrives at AV node

2) Ventricular walls contract

3) Pressure in ventricles > pressure in atria

4) AV valves close (first heart sound)

5) Isovolumic contractions (during isovolumic contraction/relaxation – all valves are closed)

6) Pressure in ventricles > aorta/pulm arteries

7) Semi lunar valves open and ejection begins

Question 27

Ventricular relaxation- Diastole

Answer 27

1) Once pressure aorta > ventricles, semi-lunar valves close – 2nd heart sound

2) Isovolumetric ventricular relaxation

3) Pulmonary veins/SVC/IVC are filling atria (forming pressure gradient between ventricles)

4) Pressure in atria > ventricles

5) AV valves open and blood passively flows into ventricles (80%)

Question 28

Atrial systole- Ventricular filling

Answer 28

1) As ventricle refill, pressure in atria and ventricles are equalising ( DIASTASIS- slows down flow into ventricles from atria)

2) Firing of SA node, causing atrial depolarisation (P wave) to increase flow into ventricles

3) When the pressure in atria = ventricles, rapid ejection starts

4) AV n is delaying the stimuli from the SA node to allow full ventricular filling and full atrial emptying