Cardiac cycle refers to a complete heartbeat from its generation to the beginning of the next beat. Cardiac events that occur from – beginning of one heart beat to the beginning of the next are called the cardiac cycle.

1. ‘Events of Cardiac Cycle
and Cardiac Output’
Presented by: Ananya Azad Hrisha

2. Contents
Cardiac Cycle
Duration Of Cardiac Cycle
Events & phases of Cardiac Cycle
Cardiac Output
Cardiac Output Measurement
Relationship of CO with BP
Summary

3. Cardiac Cycle
Refers to a complete heartbeat from its generation to
the beginning of the next beat.
Cardiac events that occur from –
beginning of one heart beat to the beginning of the next
are called the cardiac cycle.

4. Cardiac Cycle
Initiated by spontaneous generation of AP in SA node.
Cardiac cycle has :
A period of relaxation -
Diastole - during which heart fills with blood.
A period of contraction -
Systole - during which blood is ejected.

5. Cardiac Cycle
Systolic Duration=0.3 sec
Diastolic duration=0.5sec
During atrial systole, the ventricles are relaxed.
During ventricular systole, the atria are relaxed.
Calculation
For 72 beats time is 60 sec
For 1 beat=60/72=0.8 sec
Total duration of each cardiac cycle=0.8sec

6. Cardiac Cycle
Systole (0.3 s) includes:
1. Isovolumetric contraction.
2. Ejection.
Diastole (0.5 s) includes:
3. Isovolumetric relaxation.
4. Rapid ventricular filling.
5. Slow ventricular filling (diastasis).
6. Atrial contraction.

7. Cardiac Cycle
Systole
(0.3 s)
• Isovolumetric
contraction
Ejection
Reduced
Ejection
Rapid
Ejection
Diastole
Isovolumic
relaxation
Rapid
ventricular
filling
Slow
ventricular
filling
(diastasis).
Atrial
contraction

8. EVENTS IN CARDIAC CYCLE
(physiology)
'Lub-dub,' 'lub-dub' - This is the familiar sound of the
heartbeat.
The events in cardiac cycle includes –
Systole- term used to describe the contraction of the
heart.
Diastole -term used to describe the relaxation of the
heart.

9. Atrial Systole
• Blood normally flows continually from great veins
into atria :
• 75% flows directly from atria into ventricle before the
atria contracts.
• 25% of filling of ventricles – atrial contraction.

10. Atrial Systole
(The end of diastole)
• Atrial contraction is complete before the
ventricle begins to contract.
• Atrial pressure drops when the atria stop
contracting.

11. Beginning of Ven.Systole
Isovolumetric Contraction
Atrioventricular (AV) valves close at the beginning.
Mechanically, it’s the interval between the closing of the AV valves
and the opening of the semilunar valves (aortic and pulmonary
valves).
Electrically, it is the interval between the QRS complex and the end
of the T wave (the Q-T interval).

12. Ven.Systole
The AV valves close when the pressure in the
ventricles exceeds the pressure in the atria.
As the ventricles contract isovolumetrically- their
volume doesn’t change
the pressure inside increases, approaching the
pressure in the aorta and pulmonary arteries.

13. Ven. Systole
Ejection
The Semilunar valves ( aortic , pulmonary ) open at the
beginning of this phase.
at first 2/3 rapid ejection (70%) & remaining 1/3 slow
ejection (30%)
ventricles continue to contract - pressure in ventricles
exceed that of in aorta & pulmonary arteries &
semilunar valves open-blood is pumped out of ventricles
& volume decreases rapidly.

14. Ejection
 Then, pressure in the ventricles falls
below the pressure in the arteries.
 blood in the arteries begins to flow
back toward the ventricles.
 At the end of ejection, the semilunar
valves close.

15. Diastole
Isovolumetric relaxation
Relaxation of the heart.
Is in this state of relaxation(diastole)-the
pressure within the heart is low.
 The atrium in diastole has been filling
with blood on top of the closed AV valve,
causing atrial pressure to rise grad .

16. Diastole
Rapid Inflow ( Rapid Ven. Filling)
• Pressure & volume of ventricle are low in
this phase and This phase lasts for 0.06 sec.
• AV valves are open -blood accumulated in
atria flows into the ventricle.
• Ventricular volume increases rapidly - blood
flows from the atria into the ventricles.

17. Diastole
Diastasis
• Pressure in atria and ventricles rises
slowly as blood continues to return to
the heart.
• This decreases the rate of blood flow
from atria to ventricles
• causes slow filling of ventricles
called diastasis.

18. Diastole
Diastasis
• Also called reduced filling phase.
• During rapid filling and diastasis phase about 75% of blood
passes from atria to ventricles.
• Then next cycles begins with atrial contraction.
• Then Atrial Diastole begins – where the atria are relaxed after
the contraction (period of atrial relaxation for rest of
cardiac cycle) having duration of 0.7 sec.

19. Figure: Events of the Cardiac Cycle

20. Cardiac Cycle

21. Cardiac Output
Cardiac output (Q or or CO ) is the volume of blood
being pumped by the heart, , in particular by a left or
right ventricle in the time interval of one minute.
The amount of blood the heart pumps through the
circulatory system in a minute.
A normal adult has a cardiac output of 4.7 liters (5
quarts) of blood per minute.

22. Cardiac Output
The stroke volume output and the heart rate determine the
cardiac output.
Doctors think about cardiac output in terms of the following
equation:
Cardiac output = stroke volume × heart rate
(ml/min) (ml/beat) (beats/min)
 Where,
stroke volume = the amount of blood put out by the left
ventricle of the heart in one contraction
heart rate = number of times your heart beats per minute.

23. Cardiac Output
The cardiac output is usually expressed in liters/minute.
Someone weighing about 70 kg (154 lbs), the cardiac output at rest
is about 5 liters/minute.
In a resting male, CO = 70mL/beat x 75 beats/min = 5.25L/min.
 A number of clinical methods available for measurement of CO -
having unique strengths and weaknesses & relative comparison.
Is limited by the absence of a widely accepted "gold standard"
measurement.

24. Cardiac Output
MEASURING CARDIAC OUTPUT
1. The Fick principle
2. Dilution methods
3. Pulmonary artery
thermodilution (trans-right-heart
thermodilution)
4. Doppler ultrasound method
5. Impedance cardiography

25. Cardiac Output
Relationship With BP
As Cardiac output is made up of heart rate and stroke volume - at rest
these are relatively constant.
With exercise the heart beats faster - more blood is pumped out
with each beat contributing to a rise in BP.
Changes in the volume of blood within the cardiovascular system will
also affect Bp.

26. Cardiac Output
Relationship With BP
A person was severely dehydrated or lost a large quantity of
blood through a wound there would be less blood for the heart to
pump, thereby reducing cardiac output and BP.
For a typical, fit young person, the cardiac output might go up to
about 20 liters/min at the peak of exercise.
for a world-class athlete in an endurance sport, the maximum
cardiac output might be around 35 liters/min.

27. Summary
 Cardiac Cycle :all events associated with one
heartbeat, including diastole (relaxation phase) and systole
(contraction phase) of both the atria and the ventricles.
 During a cardiac cycle -
Each heart chamber goes through systole and diastole.
Correct pressure relationships are dependent on careful timing
of contractions.

28. Summary
 The sequence of events in one cardiac cycle is –
1st is atrial systole,
Followed by atrial diastole and ventricular systole,
Finally, ventricular diastole.

29. Summary
 Atrial systole (duration 0.1 sec) :Contraction of atria, increases pressure
inside atria to 4-6 mmHg in right atrium and abt. 7-8mmHg in left atrium.
 Then there is a period of atrial relaxation for rest of cardiac cycle about
duration 0.7 sec.
 Ventricular contraction (0.3 sec):Rising ventricular pressure exceeds the
atrial pressure causing closure of AV valves(tricuspid & mitral valves) -
responsible for generating 1st heart sound.
 Ventricular relaxation (0.5 sec) : called heart’s state of relaxation, the
pressure within the heart is low. blood passively flows through the atria
and into the ventricles.

30. Summary

31. Summary
Cardiac output:
The cardiac output is simply the amount of blood pumped
by the heart per minute.
Necessarily, the cardiac output is the product of the heart
rate, which is the number of beats per minute, and the
stroke volume, which is amount pumped per beat.

32. Thank You 