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CARDIOVASCULAR SYSTEM

CARDIAC CYCLELECTURE – 3

DR. ZAHOOR ALI SHAIKH

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CARDIAC CYCLE

Cardiac events occurring during one beat (systole & diastole) are repeated during the next beat

Cardiac cycle time : 0.8 second when heart rate is 75 beats per minute.

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CARDIAC CYCLE

Atria and Ventricle go through separate cycles of systole and diastole.

When we use the term Systole and Diastole, we refer to ventricles, until unless specified for atria.

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We will discuss mechanical & electrical changes during Cardiac CycleMechanical changes:

1. Phases of cardiac cycle

2. Pressure changes during cardiac cycle

3. Volume changes during cardiac cycle

4. Heart sounds

Electrical Changes

5. Electrocardiogram (ECG)

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ECGECG ( Electrocardiogram) – These electrical events can be

recorded by putting electrodes on the surface of bodyP wave – Atrial depolarizationQRS - Ventricular DepolarizationT wave – Ventricular Repolarization

We will discuss ECG in detail in coming lectures.

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MECHANICAL CHANGES1. PHASES OF CARDIAC CYCLE

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PHASES OF CARDIAC CYCLE Atrial systole: 0.1 second Atrial diastole : 0.7 seconds

Ventricular systole : 0.3 seconds Ventricular diastole : 0.5 seconds

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AD AS

VS VD

CARDIAC CYCLE

Atrial Cycle (0.8 Sec.)

Ventricular Cycle (0.8 Sec.)

0.7 Sec. 0.1 sec.

0.3Sec. 0.5 sec.

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

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Ventricular events Ventricular systole1. Isovolumetric contraction 2. Ejection phase

Rapid ejection Slow ejection

Protodiastolic phase

Ventricular Diastole1. Isovolumetric relaxation phase2. Filling phase

Rapid filling Slow filling Last rapid filling

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Ventricular events

Ventricular systole

1. Isovolumetric Contraction When blood has come from Atria into

the ventricle, ventricle will start contracting, when pressure increases in ventricle than atria, AV valves close.

This phase of ventricular contraction when all valves are closed is called ISOVOLUMETRIC CONTRACTION.

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Ventricular systole During Isovolumetric Contraction,

volume remains same, but pressure in the ventricle must continue to increase till it exceeds aortic pressure.

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Ventricular systole

2. Ejection Phase When ventricular pressure increases,

semi-lunar valve [aortic and pulmonary valves] will open and blood will flow into aorta and pulmonary artery. This is Ejection Phase [pumping of blood out].

Ejection is rapid first and then slow.

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Protodiastolic phase Once ventricle muscle is fully

contracted, than it will relax and ventricular pressure will drop rapidly.

When ventricles are relaxing, but aortic and pulmonary valves have not closed yet, this period is called Protodiastole.

It lasts for 0.04 sec. It ends when aortic and pulmonary valve

close.

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Ventricular Diastole

1. Isovolumetric Relaxation

During diastole, When ventricular pressure falls below the Aortic pressure, aortic valve closes, and AV valves are not open yet , ventricle is close cavity with all valves closed. This phase is called Isovolumetric Relaxation (means volume remains same but pressure is decreasing).

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Ventricular Diastole2. Filling phase When ventricular pressure falls below the atrial pressure, AV

valve open and blood moves rapidly from the atria into the ventricles – first rapid filling phase [causes 3rd heart sound].

Then blood comes slowly – slow filling phase. Then atria contract for 0.1sec and blood comes fast into the

ventricle – last rapid filling phase [causes 4th heart sound].

NOTE

Last rapid filling phase is due to atrial systole and contributes to 20-30% of ventricular filling.

After atrial systole, cardiac cycle will re-start.

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AD AS

VS VD

Relation Of Heart Sounds With Phases Of Cardiac Cycle

HEART SOUNDS

0.7 Sec. 0.1 sec.

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

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Tachycardia, Effect on Cardiac Cycle During Tachycardia, when heart rate is

increased, both systole and diastole time decreases.

Diastole length (time) is shortened much more than systole length. Therefore it

reduces the time for ventricular relaxation and filling.

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2. PRESSURE CHANGES DURING CARDIAC CYCLE

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Pressure changes during cardiac cycle

Rt- Atrium = 0-7mm Hg.

Lt- Atrium = 2-10 mm Hg.

Rt – Ventricle = 25 / 6(2-8) mm Hg.

Lt – ventricle = 120 / 8(2-10) mm Hg.

Aorta = 120 / 80 mm Hg.

Pul. Artery = 25 / 10 mm Hg.

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Draw pressure curve for Lt.ventricle, Aorta & Lt. Atrium

Draw pressure curve for Rt. Ventricle &

Pul. Artery.

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Events of cardiac cycle showing pressure changes in left ventricle, aortic pressure, atrial pressure, ECG & phonocardiogram

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pressure curves for Rt. ventricle. & Pulmonary Artery

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3. VOLUME CHANGES DURING CARDIAC CYCLE

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Define Stroke Volume (SV)

Define End Diastolic Volume (EDV)

Define End Systolic Volume (ESV)

Define Ejection Fraction (EF)

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Stroke Volume: It is a volume of blood pumped out

by each ventricle per beat. It is about 70 - 80 ml.

Stroke volume (SV) = EDV – ESV

End Diastolic Volume: Volume of blood in each

ventricle at the end of diastole.

It is about 120 – 130 ml.

End Systolic Volume: Volume of blood in each

ventricle at the end of Systole. It is about 50 to 60 ml

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Volume changes during cardiac cycle

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Events of cardiac cycle showing left ventricular pressure, volume changes, & phonocardiogram

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Ejection fraction (EF) is the percentage of ventricular end diastolic volume (EDV) which is ejected with each stroke.

EF = SV (EDV – ESV)

EDVX 100

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120X 100 = 62.5%

Normal ejection fraction is about 60 – 65 %.

Ejection fraction is good index of ventricular function.

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Heart Sounds

We will discuss Heart Sounds in next lecture.

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What You Should Know From This Lecture

Cardiac Cycle – Definition Phases of Cardiac Cycle Pressure Changes Volume Changes Period of Systole & Diastole During

Tachycardia Relationship of Heart sounds with

Cardiac Cycle

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Thank you