Cardiac cycle

Blood Flow Through Heart

CARDIAC CYCLE

• The normal duration of the cardiac cycle is 0.8 second.

• Each beat of the heart consists of systole and diastole of atria and ventricles.

• Systole is the contraction of the heart during which blood is ejected out from the heart

• Diastole is the relaxation of the heart during which the chambers of the heart are filled with blood

Cycle Length

FACTS TO REMEMBER

• SYSTOLE IS CONTRACTION-THE RISE IN PRESSURE IN THE CONTRACTING CHAMBER -BLOOD BEING EJECTED BY THE CONTRACTING CHAMBER

• DIASTOLE IS RELAXATION- A FALL IN PRESSURE OF THE RELAXING CHAMBER- FILLING OF THE RELAXING CHAMBER

END DIASTOLIC VOLUME 110 - 120 ml

STROKE VOLUME 70 ml

END SYSTOLIC VOLUME 40 - 50 ml

SV = EDV-ESV

DURATION OF CARDIAC CYCLE α 1 HR

Cardiac cycle - the total picture

The normal duration of the cardiac cycle is 0.8 sec.

ATRIAL EVENTS:• Atrial Systole - 0.1 sec• Atrial Diastole - 0.7 sec

VENTRICULAR EVENTS:• Ventricular systole - 0.3 sec• Ventricular diastole - 0.5 sec

• Ventricular Systole:

1. Isovolumetric contraction phase - 0.05 sec

2. Rapid Ejection phase - 0.10 sec

3. Reduced Ejection phase - 0.15 sec

Ventricular diastole

1. Proto diastolic phase - 0.04 sec

2. Isovolumetric Relaxation phase - 0.06 sec

3. First Rapid filling phase - 0.10 sec

4. Slow Filling or Diastasis - 0.20 sec

5. Last Rapid Filling Phase - 0.10 sec

Events in the cardiac cycle

• Initially, during diastole, all the four chambers

of the heart ie both atria and ventricles are

relaxed and filled with blood due to venous

return.

ATRIAL SYSTOLE The end of diastole

• Atrial systole: 0.1 sec.

• Atrial pressure rises.

• Right atrial : 4-6 mmHg

• Left atrial : 7-8 mmHg

Ventricular systole

Duration 0.3 sec. It has 3 phases.

1. Isovolumetric contraction phase: 0.05 sec

2. Rapid ejection phase: 0.10 sec

3. Reduced ejection phase: 0.15 sec

ISOVOLUMETRIC CONTRACTION

The Beginning of systole After the ventricles have filled by atrial

contraction, AV (Atrio-ventricular) valves close as the ventricles begin their contraction and intraventricular pressure increases .

The semilunar valves remain closed and this makes ventricle a closed cavity.

The volume in the ventricles remains unchanged throughout the contraction, hence the name isovolumetric.

Closure of the AV valves in this phase causes the first heart sound.

RAPID EJECTION

The semilunar valves (aortic and pulmonary) open at the beginning of this phase.

2/3rd of stroke volume ejected

Aortic pressure increases but slightly less than ventricles

REDUCED EJECTION The end of systole

The continued contraction of the ventricles pushes the remaining blood into the blood vessels ( Aorta and pulmonary artery) slowly.

At the end of this phase the ventricles begin to relax.

PROTODIASTOLIC PHASE

• When ventricles begin to relax, the AV valves close and the semilunar valves remain open.

• As the intra ventricular pressure decreases below the pressure in the aorta and pulmonary artery, the blood tries to come back into the ventricles.

• This is prevented by closure of semilunar valve which produces the second heart sound

ISOVOLUMETRIC RELAXATION The beginning

of DiastoleIn this phase, the ventricle is in a closed cavity, which is relaxing

During this phase the intra ventricular pressure goes below the atrial pressure.

FIRST RAPID VENTRICULAR FILLING

Since there is reduced intra ventricular pressure in this phase, causing the semilunar valves to close.

The AV valves open and there is sudden rush of blood into the ventricles from the atria.

REDUCED VENTRICULAR FILLING (Diastasis)

During this phase both atria and ventricles are relaxing ,the AV valve is open.

The blood entering the atria,fill the ventricles passively.

Last rapid filling phase

• This phase coincides with atrial contraction. The atria are in systole forcing blood into the ventricles which are relaxed.

PRESSURE CHANGES DURING CARDIAC CYCE

• Chambers of the heart show different pressures during the various phases of the cardiac cycle.

• Left ventricle will have higher pressure than right ventricle and both atria have lower pressures.

• During ventricular systole, LV pressure reaches a maximum of 120-140 mm Hg and RV pressure reaches a maximum of 25-30 mm Hg.

• During ventricular diastole, LV pressure drops to about 15-20 mm Hg and RV pressure drops to 0 mm Hg.

• Aortic pressure changes: At the beginning of rapid ejection phase 120 mm Hg and at the beginning of ventricular diastole 80 mm Hg.

• Pulmonary artery pressure changes during ventricular systole will reach a maximum of 25-30 mm Hg and during ventricular diastole it reduces to 0 mm Hg.

• Atrial pressure varies between 0 mm Hg when relaxing to a maximum of 15-20 mm Hg during contraction.

HEART SOUNDS

• First heart sound : It is due to the closure of AV valves ( mitral and

tricuspid valves) . Heard as LUB Duration is 0.09 to 0.15 seconds It is characterized by prolonged ,loud sound

and best heard at mitral and tricuspid areas

Second heart sound: : • It is due to the closure of semilunar valves.

Heard as DUP, Duration is 0.10 seconds It is characterized by short,sharp sound and

best heard at aortic and pulmonary areas.