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CARDIOVASCULAR SYSTEM CARDIAC CYCLE. LECTURE – 3 DR. ZAHOOR ALI SHAIKH. 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. CARDIAC CYCLE.

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cardiovascular system cardiac cycle

CARDIOVASCULAR SYSTEM CARDIAC CYCLE

LECTURE – 3

DR. ZAHOOR ALI SHAIKH

cardiac cycle
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.
cardiac cycle1
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.
we will discuss mechanical electrical changes during cardiac cycle
We will discuss mechanical & electrical changes during Cardiac Cycle

Mechanical changes:

  • Phases of cardiac cycle
  • Pressure changes during cardiac cycle
  • Volume changes during cardiac cycle
  • Heart sounds

Electrical Changes

  • Electrocardiogram (ECG)
slide6
ECG
  • ECG ( Electrocardiogram) – These electrical events can be recorded by putting electrodes on the surface of body
  • P wave – Atrial depolarization
  • QRS - Ventricular Depolarization
  • T wave – Ventricular Repolarization

We will discuss ECG in detail in coming lectures.

phases of cardiac cycle
PHASES OF CARDIAC CYCLE
  • Atrial systole: 0.1 second
  • Atrial diastole : 0.7 seconds
  • Ventricular systole : 0.3 seconds
  • Ventricular diastole : 0.5 seconds
cardiac cycle2
CARDIAC CYCLE

Atrial Cycle (0.8 Sec.)

Ventricular Cycle (0.8 Sec.)

ventricular events
Ventricular events
  • Ventricular systole
  • Isovolumetric contraction
  • Ejection phase
          • Rapid ejection
          • Slow ejection
  • Protodiastolic phase
  • Ventricular Diastole
    • Isovolumetric relaxation phase
    • Filling phase
          • Rapid filling
          • Slow filling
          • Last rapid filling
ventricular events1
Ventricular events

Ventricular systole

  • 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.
ventricular systole
Ventricular systole
  • During Isovolumetric Contraction, volume remains same, but pressure in the ventricle must continue to increase till it exceeds aortic pressure.
ventricular systole1
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.
protodiastolic phase
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.
ventricular diastole
Ventricular Diastole
  • 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).

ventricular diastole1
Ventricular Diastole

2. 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.

relation of heart sounds with phases of cardiac cycle
Relation Of Heart Sounds With Phases Of Cardiac Cycle

1 st Heart Sound

2 nd Heart Sound

3 rd Heart Sound

4 th Heart Sound

HEART SOUNDS

tachycardia effect on cardiac cycle
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.

pressure changes during cardiac cycle
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.

slide24
Draw pressure curve for Lt.ventricle, Aorta & Lt. Atrium
  • Draw pressure curve for Rt. Ventricle &

Pul. Artery.

slide25
Events of cardiac cycle showing pressure changes in left ventricle, aortic pressure, atrial pressure, ECG & phonocardiogram
slide28
Define Stroke Volume (SV)
  • Define End Diastolic Volume (EDV)
  • Define End Systolic Volume (ESV)
  • Define Ejection Fraction (EF)
slide29
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
slide32

SV (EDV – ESV)

X 100

EDV

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

EF =

75

X 100 = 62.5%

120

Normal ejection fraction is about 60 – 65 %.

Ejection fraction is good index of ventricular function.

heart sounds
Heart Sounds
  • We will discuss Heart Sounds in next lecture.
what you should know from this lecture
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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