Prof. Sultan Ayoub MeoMBBS, M.Phil, Ph.D (Pak), PG Dip Med Ed, M Med Ed (Scotland)

FRCP (London), FRCP (Dublin), FRCP (Glasgow), FRCP (Edinburgh)Professor and Consultant, Department of Physiology,

College of Medicine, King Saud University, Riyadh, Saudi Arabia

CARDIC CYCLE CARDIC CYCLE

LECTURE OUTLI NES / OBJECTIVESLECTURE OUTLI NES / OBJECTIVES

General principle of the cardiac cycle

Identify events occurring during cardiac cycle:

mechanical, electrical, volume & pressure

changes, heart sounds. Understand the various phases of the cardiac

cycle

STUDENTS ABLE TO UNDERSTAND:

CARDIAC CYCLE

The cardiac events that occur from the beginning of one heart beginning of one heart

beat to the beginning of the nextbeat to the beginning of the next is called the is called the cardiac cycle.cardiac cycle.

Cardiac cycle is a complete beat of the heart.

Each cycle is initiated by spontaneous generation of an action

potential in the sinus node.

The cardiac cycle consists of a period of relaxation called

diastole during which the heart fills with blood. This period is

followed by a period of contraction called systole.

CARDIAC CYCLE: CARDIAC VALVES

CARDIAC CYCLE: CARDIAC VALVES

CARDIAC CYCLE: CARDIAC VALVES

PRESSURES IN THE CARDIAC CHABERS

Aortic pressure (left ventricular pressure)Maximum pressure (during systole): 120 mm Hg.Minimum pressure (during dystole): 80 mm Hg.Pulse pressure (difference between systolic and diastolic) : 120-80 = 40 mm Hg.Right ventricular pressure Maximum pressure = 25mm HgMinimum pressure = 0-2mm HgAtrial pressureMaximum right atrial pressure 6-8 mm HgMinimum right atrial pressure 0-2 mm Hg Maximum left atrial pressure 6-9 mm HgMinimum left atrial pressure 0-2 mm Hg Pulmonary pressure (mm Hg)Systolic pulmonary arterial pressure: 25Diastolic pulmonary arterial pressure : 8

CARDIAC CYCLE

I. VENTRICULAR SYSTOLE

Iso-volumetric contraction of ventricles (0.05 sec ) Maximum ejection phase (0.112sec)Reduced ejection phase. (0.141 sec )

-------------0.303 Sec

2. VENTRICULAR DIASTOLEProtodiastole (0. 033 sec)Isovolumetric (isovolumic ) relaxation (0. 071 sec)Rapid inflow (0.110 sec)Reduced inflow (0.161 sec) Atrial systole (0.12 sec )

-------------- 0.495 sec. [0.8 Sec]

CARDIAC CYCLE: DURATION OF SYSTOLE AND DIASTOLE

0.3Sec. 0.5 sec.

VS VD

CARDIAC CYCLE: VENTRICULAR SYSTOLE

Isovolumetric contraction: The left ventricle begins to

contract, at this stage the pressure in the ventricles is slightly

above 0-2mm Hg.

As the intra-ventricular pressure rises, it pushes the cusps of the

A-V valve up and the A-V orifices are closed.

The pressure in the ventricular cavities continues to rise but

remains less than that in the large arteries. Thus, the semilunar

valves (aortic and pulmonary) also remain closed and no blood

enters or leaves the ventricles.

CARDIAC CYCLE: VENTRICULAR SYSTOLE

MAXIMUM EJECTION PHASE: The ventricles contract and

increase the pressure more than in the large arteries.

The left ventricular pressure rises up to 120 mm Hg causes the

opening of the aortic valves

Right ventiricular presssure rises more than 25 mm Hg and

causes the opening of pulmonary valves so blood leaves the

ventricles rapidly to the aorta and pulmonary artery

At the end of this stage, intraventricular pressure reaches its

peak level.

CARDIAC CYCLE: VENTRICULAR SYSTOLE

REDUCED EJECTION PHASE

In this phase of the cardiac cycle, the force of contraction of

the ventricles becomes weaker than the force of contraction

during the maximum ejection phase. Now the pressure within

the ventricles also decreases, but is still higher than that of the

aorta so ventricular emptying continues.

In this phase less volume of blood flows into the aorta and

pulmonary artery due to weaker contraction of the ventricles.

CARDIAC CYCLE: VENTRICULAR SYSTOLE

CARDIAC CYCLE: VENTRICULAR SYSTOLE

CARDIAC CYCLE: VENTRICULAR SYSTOLE

VENTRICULAR DIASTOLE [PROTO DIASTOLE]

In this stage, the ventricles relax and the intraventricular

pressure decreases, becoming less than the aortic and

pulmonary artery pressures.

Blood present in the aorta and pulmonary artery tends to

move back into the ventricles.

At this stage the semilunar valves ( aortic and pulmonary )

are closed and do not allow entry of blood into the ventricles

CARDIAC CYCLE: VENTRICULAR DIASTOLE

ISOVOLUMETRIC RELAXATION

•In this stage the ventricles relax further and intraventricular

pressure falls.

•The semilunar valves remain closed due to higher pressure in

the large arteries as compared to intraventricular pressure.

•The pressure within the ventricles is still higher than the atria,

so the A-V valves remain closed and no blood enters or leaves

the ventricles.

CARDIAC CYCLE: VENTRICULAR DIASTOLE

CARDIAC CYCLE: VENTRICULAR DIASTOLE

RAPID INFLOW

The ventricular volume increases, the pressure within the

ventricles is further decreased to lower than intra atrial

pressure. The left ventricular pressure decreases up to 2-4 mm

Hg. This pressure is less than the maximum left atrial pressure

(6-9mm Hg). This change in pressure causes the opening of

left AV (biscuspid / mitral) valve. So blood which was

accumulate in the left atrium rush into the left ventricle.

CARDIAC CYCLE: VENTRICULAR DIASTOLE

RAPID INFLOW

Right ventricular pressure decreased up to 0-2mm Hg. This

pressure is less than the maximum right atrial pressure (6-8mm

Hg). This change in pressure causes the opening of right AV

(tricuspid) valve. So the blood which was accumulate in the

right atrium rush into the right ventricle.

CARDIAC CYCLE: VENTRICULAR DIASTOLE

CARDIAC CYCLE: VENTRICULAR DIASTOLE

CARDIAC CYCLE

Reduced inflow

At the beginning of this phase most of the blood has already

entered the ventricles.

Remaining blood in the atria also flows into the ventricles.

Atrial systole

Once again the atrial muscle fibers start to contract, indicating

the beginning of a new cardiac cycle.

CARDIAC CYCLE: VENTRICULAR DIASTOLE

SUMMARY CARDIAC CYCLE EVENTS: OPENING AND CLSOSING OF VAVLVES

CARDIAC CYCLE: ASSOCIATION WITH HEART SOUNDS

CARDIAC CYCLE: ASSOCIATION WITH HEART SOUNDS

CARDIAC CYCLE: ASSOCIATION WITH

HEART SOUNDS

VS VD

CARDIAC CYCLE: ASSOCIATION WITH HEART SOUNDS

HEART SOUNDS

0.3Sec. 0.5 sec.

1 st Heart Sound 2 nd Heart Sound 3 rd Heart Sound 4 th Heart Sound

AS – Atrial Systole; AD – Atrial Diastole ; VS – Ventricular systole; VD – Ventricular diastole

Ventricular Systole

0.3Sec.

1 st Heart Sound 2 nd Heart Sound

Isovolumetric contraction

period

Maximum ejection

period

Reduced ejection

period

AS – Atrial Systole; AD – Atrial Diastole ; VS – Ventricular systole; VD – Ventricular diastole

CARDIAC CYCLE: ASSOCIATION WITH HEART SOUNDS

Ventricular Diastole

0.5Sec.

1 st HS

2 nd HS

Isovolumetric Relaxation

Phase

Maximum Filling

Phase

Reduced Filling

Phase

4 th HS

3 rd HS

HS – Heart Sound

Protodiastolic Period

CARDIAC CYCLE: ASSOCIATION WITH HEART SOUNDS

TAKE HOME MESSAGE

Beginning of one heart beat to the beginning of the next is

called the cardiac cycle. consists of a period of relaxation called

diastole followed by a period of contraction called systole.

Cycle duration is 0.8 Sec [Systole 0.3 sec and Diastole 0.5 Sec]

THANK YOU THANK YOU

College of Medicine, King Khalid University College of Medicine, King Khalid University Hospital, King Saud University, Riyadh, Hospital, King Saud University, Riyadh,

Saudi ArabiaSaudi Arabia