This document provides an introduction to concepts related to cardiac output. It defines cardiac output as the volume of blood pumped by the heart each minute. A normal resting cardiac output for an adult male is approximately 5 liters per minute. Cardiac output can increase during exercise, reaching as high as 20 liters per minute. Other factors that affect cardiac output are defined, such as stroke volume, ejection fraction, preload, contractility, and afterload. The relationship between these factors and how they regulate cardiac output is also explained.

1. An Introduction to Cardiology
Nikhil Vaishnav, Clinical Coordinator
Department of Paramedical & Health Science

2. Cardiac output
CHAPTER-8

3. Introduction
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• Cardiac output is described as the amount of blood heart pumps each
minute.
• Cardiac output (CO) is the volume of blood ejected from the left ventricle
(or the right ventricle) into the aorta (or pulmonary trunk) each minute.
• Cardiac output is related to the quantity of blood delivered to various parts
of the body.
• It is an important indicator of how efficiently the heart can meet the body's
demands for perfusion.
 Cardiac output is expressed in terms of litres per min .

4. Image source : Google
In a typical resting adult male , Stroke volume is approximately 70 ml/
beat & heart rate is 72 per minute .
 Therefore Cardiac output is 70 X 72 = 5 litre per minute .
 Factors that increase stroke volume or heart rate normally increase CO.
During mild exercise cardiac output would be 10 L/ min.
During intense exercise CO would reach up to 20 L/ min.
The normal range for cardiac output is about 4 to 8 L/min.
It can vary depending on the body's metabolic needs.
Cardiac output is important indicator as it predicts oxygen delivery to cells

5. Cardiac output

6. Cardiac output

7. Cardiac output

8. Cardiac reserve
Cardiac reserve
 Cardiac reserve refers to
the difference between the
rate at which
the heart pumps blood and
its maximum capacity for
pumping blood at any given
time.
 Cardiac reserve is the
difference between a
person’s maximum cardiac
output and cardiac output at
rest

9. Cardiac reserve
The average person has a cardiac
reserve of 4 or 5 times the resting
value.
 Top endurance athletes may have
a cardiac reserve 7 or 8 times their
resting cardiac output.
 People with severe heart disease
may have little or no cardiac reserve

10. Cardiac index(CI)
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 The cardiac index(CI) is an assessment of the cardiac output value based on
the patient’s size.
 Cardiac index (CI) is a haemodynamic parameter that relates the cardiac
output (CO) from left ventricle in one minute to body surface area (BSA).
CI relates heart performance to the size of the individual.
The unit of measurement is litres per minute per square meter (L/min/m2)
 The normal range for CI is 2.5 to 4 L/min/m2.

11. Cardiac index

12. Cardiac index

13. BSA calculation

14. Ejection fraction
 Ejection fraction (EF) is a measurement, expressed as a percentage, of how
much blood the left ventricle pumps out with each contraction.
 An ejection fraction of 60 percent means that 60 percent of the total
amount of blood in the left ventricle is pushed out with each heartbeat.
 A normal heart’s ejection fraction may be between 50 and 70 percent.
 Preserved ejection fraction (HFpEF) – also referred to as diastolic heart
failure. The heart muscle contracts normally but the ventricles do not relax
as they should during ventricular filling .
 Reduced ejection fraction (HFrEF) – also referred to as systolic heart failure.
The heart muscle does not contract effectively, and therefore less oxygen-
rich blood is pumped out to the body.

15.  A ejection fraction measurement under 40 percent may be evidence
of heart failure or cardiomyopathy.
 An EF from 41 to 49 percent may be considered “borderline.”. It may
indicate damage from heart attack .
 In severe cases, ejection fraction can be very low.
 An ejection fraction measurement higher than 75 percent may indicate
a heart condition such as hypertrophic cardiomyopathy.

16. Tests for measuring EF
 Echocardiogram: Most widely used test to measure EF.
 MUGA scan.
 CAT scan
 Cardiac catheterization
Nuclear stress test

17. Ejection fraction

18. Ejection fraction formula

19. Ejection fraction

20. Stroke volume
 Stroke volume is the amount of blood ejected from the ventricle with each
cardiac cycle or each beat.
 Stroke Volume (SV) is the volume of blood in milliliters ejected from
the each ventricle due to the contraction of the heart muscle which
compresses these ventricles.
 Normal values for a resting healthy individual would be approximately 60-
100mL.
 Stroke volume= End diastolic volume(EDV) – End systolic volume(ESV).
 Stroke volume is regulated by 3 factors preload , contractility & afterload.

21. Stroke volume

22. End Diastolic volume(EDV)
EDV refers to amount of blood in the left or right ventricle at the end of
diastole, just before systole starts.
 For an average-sized man, the end-diastolic volume is 120 milliliters of
blood
 EDV is used to estimate preload and ejection fraction , stroke volume.
 EDV is affected by conditions such as cardiomyopathy and mitral
regurgitation.

23. End systolic volume(ESV)
End systolic volume (ESV) is the amount of blood that remains in a ventricle of
the heart at the end of systole.
 The ESV for an average adult male at rest is usually about 50 ml.
 The main factors that affect the end-systolic volume are afterload and the
contractility of the heart.

24. Regulation of stroke volume
 Preload
 Contractility
 Afterload

25. Preload
Preload is also known as left ventricular end-diastolic pressure (LVEDP).
 It is the amount of ventricular stretch at the end of diastole.
 It is related to ventricular filling.
 It is the initial stretching of the cardiac myocytes prior to contraction.
 The preload is proportional to End diastolic volume (EDV).
 If preload is more , EDV is more, heart fills with more blood then greater the
force of contraction during systole

26. EDV determined by 2 main factors: the duration of ventricular filling and
venous return.
If Heart rate is more , diastole time is lesser, EDV is less , ventricle contract
before they filled adequate .
If heart rate is more than 160 bpm, SV declines due to short filling time.

27. 

28. Factors affecting preload

29. 

31. Frank Starling law
 The Frank-Starling relationship is based on the link between the
initial length of myocardial fibers and the force generated by
contraction.
 The Frank-Starling relationship is the observation that ventricular
output increases as preload (end-diastolic pressure) increase

32. Frank starling law


33. 

34. Contractility
Contractility is the strength of contraction at any given preload.
During constant preload positive inotropic agents increase calcium inflow
during cardiac action potential , thus increase force of contraction.
 Inhibition of the sympathetic division , anoxia, acidosis, hyperkalemia,
some Anesthetics & CCB have negative Inotropic effects.

36. Afterload
 Afterload is the force or load against which the heart has to contract to
eject the blood.
 Afterload is the ‘load’ to which the heart must pump against.
 Afterload goes down when aortic pressure and systemic vascular
resistance decreases through vasodilation. HTN & Atherosclerosis increases
Afterload.

37. Decreased stroke volume
More blood remains in the ventricle(ESV)
Increased afterload

41. Preload & Afterload

42. Variations in cardiac output
Physiological variations :
Sex: Cardiac output is 10-20 % less in females.
 Age: At birth CO is 2.5 litre/min . At 10 years of age it becomes 4 litre/min.
CO declines in old age .
 Exercise: With high intense exercise CO reach even up to 35 L/min.
 After food intake it is increased about 30 %.
 Emotions like excitement, anxiety etc increase CO.
A high environmental temperature can increase the cardiac output .
Posture: A change in posture from lying to standing produces a slight
decrease in CO

43. Pathological variations:
Cardiac output is increased pathologically in fever, hyperthyroidism.
 Cardiac output is decreased in Myocardial infraction, hemorrhage,
shock, cardiac failure, arrhythmias etc.

44. Factors affecting cardiac output
 Diastolic volume: According to Frank-starling’s law End diastolic
volume(EDV) is more, the more will be myocardium stretching and the
force of contraction will be increased.
 Venous return: It is the quantity of food flowing from great veins into
the right atrium per minute . If venous return is more due to any reason ,
EDV is more , thus increased stroke volume.

45. Afterload: It is the quantity of food flowing from great veins into the right
atrium per minute. If venous return is more due to any reason , EDV is more ,
thus increased stroke volume.
 Heart rate: CO is directly proportional to heart rate .

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