doctor cardiac output slides

1. CARDIAC OUTPUT

2. ◻ Cardiac output is the quantity of blood pumped
into the aorta each minute by the heart.
Cardiac output
is expressed by the following equation:
Cardiac output = Stroke volume x Heart rate
◻ Venous return is the quantity of blood flowing
from the veins into the right atrium each minute.

3. CARDIAC OUTPUT IS EXPRESSED IN THREE
WAYS:
◻ Stroke volume: is the amount of blood pumped out by each ventricle
during each beat. It is expressed by the following equation:
Stroke volume= End diastolic volume - End systolic volume
◻ Minute volume: is the amount of blood pumped out by each ventricle
in one minute.
◻ Minute volume = Stroke volume × Heart rate
◻ Cardiac index: is the minute volume expressed in relation to square
meter of body surface area.

4. Ejection fraction: is the fraction of end diastolic volume that is ejected out by
each ventricle.
◻ is the fraction of the end-diastolic volume ejected in each stroke volume.
◻ is related to contractility.
◻ is normally 0.55 or 55%.
◻ is expressed by the following equation
◻ Cardiac reserve: is the maximum amount of blood that can be pumped out by
heart above the normal value.

5. Stroke work
is the work the heart performs on each beat.
is equal to pressure ë volume. For the left ventricle, pressure is aortic pressure
and volume is stroke volume. is expressed by the following equation:

6. GENERAL FACTORS AFFECTING CARDIAC
OUTPUT
◻ The following factors, among others, directly affect cardiac output:
(1) the basic level of body metabolism
(2) whether the person is exercising
(3) the person’s age
(4) the size of the body

7. FORCE OF CONTRACTION
PRELOAD
◻ Preload is the stretching of the cardiac muscle fibers at the end of diastole,
just before contraction.
◻ Force of contraction of heart and cardiac output are directly proportional
to preload.
AFTERLOAD
◻ Afterload is the force against which ventricles must contract and eject the
blood.
◻ Force of contraction of heart and cardiac output are inversely
proportional to afterload.

8. PERIPHERAL RESISTANCE
◻ Peripheral resistance is the resistance offered to blood flow at the
peripheral blood vessels.
◻ when the total peripheral resistance is exactly normal, the cardiac output is
also normal.
◻ when the total peripheral resistance increases above normal, the cardiac
output falls;
◻ when the total peripheral resistance decreases, the cardiac output
increases.
◻ Cardiac output = Arterial pressure/ Total peripheral resistance

9. THE HEART HAS LIMITS FOR THE CARDIAC
OUTPUT THAT IT CAN ACHIEVE
◻ Normal cardiac output curve, showing the cardiac output per minute at each
level of right atrial pressure. This is one type of cardiac function curve .

10. FACTORS THAT CAUSE A HYPEREFFECTIVE
HEART
Factors That Cause a Hypereffective Heart:
◻ (1) nervous stimulation (2) hypertrophy of the heart muscle.
Nervous Excitation Can Increase Heart Pumping:
◻ (1) sympathetic stimulation (2) parasympathetic inhibition
Heart Hypertrophy Can Increase Pumping Effectiveness:
◻ This factor increases the plateau level of the cardiac output curve,
sometimes 60 to 100 percent, and therefore allows the heart to pump much
greater than usual amounts of cardiac output.

11. Factors That Cause a Hypoeffective Heart:
◻ Increased arterial pressure against which the heart
must pump
◻ Inhibition of nervous excitation of the heart
◻ Pathological factors that cause abnormal heart
rhythm
◻ Coronary artery blockage
◻ Valvular heart disease
◻ Congenital heart disease
◻ Myocarditis
◻ Cardiac hypoxia

12. ROLE OF THE NERVOUS SYSTEM IN
CONTROLLING CARDIAC OUTPUT
◻ Effect of the Nervous System to Increase the Arterial Pressure
During Exercise

13. PATHOLOGICALLY HIGH OR LOW CARDIAC
OUTPUTS
High Cardiac Output Caused by Reduced Total Peripheral
Resistance:
◻ Some of the conditions can decrease the peripheral resistance and at the
same time increase the cardiac output to above normal.
1. Arteriovenous (AV) fistula
2. Hyperthyroidism. In hyperthyroidism, the metabolism of most tissues of the
body becomes greatly increased
3. Anemia.
(In anemia, two peripheral effects greatly decrease total peripheral
resistance. One is reduced viscosity of blood and second diminished
oxygen to tissue)

14. LOW CARDIAC OUTPUT
◻ These conditions fall into two categories:
(1) abnormalities that decrease pumping effectiveness of the heart
(2) those that decrease venous return
Decreased Cardiac Output Caused by Cardiac Factors:
(1) Severe coronary blood vessel blockage and consequent myocardial
infarction
(2) Severe valvular heart disease
(3) Myocarditis
(4) Cardiac tamponade
(5) Cardiac metabolic derangements
(6) Leading to cardiac shock

15. CARDIAC OUTPUT CURVES USED IN THE
QUANTITATIVE ANALYSIS
Effect of External Pressure Outside the Heart on
Cardiac Output Curves
◻ Shows the effect of changes in external cardiac
pressure on the cardiac output curve.
◻ Some of the factors that can alter the external
pressure on the heart and thereby shift the cardiac
output curve are the following:
1. Cyclical changes of intrapleural pressure during
respiration
2. Breathing against a negative pressure
3. Positive pressure breathing
4. Cardiac tamponade

16. Cardiac and vascular function curves
are simultaneous plots of cardiac output and venous return as a function of right
atrial pressure or end-diastolic volume.
The cardiac function (cardiac output) curve
depicts the Frank–Starling relationship for the ventricle.
shows that cardiac output is a function of end-diastolic volume.
It states that the stroke volume of the left ventricle will increase as the left
ventricular volume increases due to the myocyte stretch causing a more forceful
systolic contraction.
The vascular function (venous return) curve
depicts the relationship between blood flow through the vascular system (or
venous return) and right atrial pressure.

17. DECREASE IN CARDIAC OUTPUT CAUSED BY NONCARDIAC
PERIPHERAL FACTORS—DECREASED VENOUS RETURN:
◻ Anything that interferes with venous return also can lead to decreased
cardiac output. Some of these factors are the following :
1. Decreased blood volume
2. Acute venous dilation
3. Obstruction of the large veins
4. Decreased tissue mass, especially decreased skeletal muscle mass
5. Decreased metabolic rate of the tissues

18. VENOUS RETURN CURVES
◻ The following three principal factors that affect venous return to the heart
from the systemic circulation:
1. Right atrial pressure
2. Degree of filling of the systemic circulation (measured by the mean
systemic filling pressure)
3. Resistance to blood flow

19. NORMAL VENOUS RETURN CURVE
◻ the venous return curve relates venous return to right atrial pressure.
◻ A slight rise in right atrial pressure causes a drastic decrease in venous
return.
◻ Both the arterial and the venous pressures come to equilibrium when all
flow in the systemic circulation ceases at a pressure of 7 mm Hg, which, by
definition, is the mean systemic filling pressure.

20. 1. is the point at which the vascular function curve
intersects the x-axis.
2. equals right atrial pressure when there is “no flow”
in the cardiovascular system.
3. is measured when the heart is stopped
experimentally.
4. Under these conditions, cardiac output and venous
return are zero, and pressure is equal throughout
the cardiovascular system.
5. is increased by an increase in blood volume or by a
decrease in venous compliance.
6. An increase in mean systemic pressure is reflected
in a shift of the vascular function curve to the right.
7. Mean systemic pressure is decreased by a
decrease in blood volume or by an increase in
venous compliance.
8. A decrease in mean systemic pressure is reflected
in a shift of the vascular function curve to the left.
Mean systemic pressure

21. b. Slope of the venous return curve
(1) is determined by the resistance of the arterioles
(1) A clockwise rotation of the venous return curve
indicates a decrease in total peripheral resistance
(TPR).
(2) When TPR is decreased for a given right atrial
pressure, there is an increase in venous return (i.e.,
vasodilation of the arterioles “allows” more blood to
flow from the arteries to the veins and back to the
heart).
(3) A counterclockwise rotation of the venous return
curve indicates an increase in TPR.
(4) When TPR is increased for a given right atrial
pressure, there is a decrease in venous return to the
heart (i.e., vasoconstriction of the arterioles
decreases blood flow from the arteries to the veins
and back to the heart)

22. Combining cardiac output and venous
return curves
When cardiac output and venous return
are simultaneously plotted as a function of
right atrial pressure, they intersect at a
single value of right atrial pressure.
The point at which the two curves intersect
is the equilibrium, or steady-state, point.
Equilibrium occurs when cardiac output
equals venous return.