physiology of heart

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PHYSIOLOGY Cardiac Output, Venous Return and Their Regulation

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Cardiac Output and Venous Return

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Page 1: Physiology of Heart

PHYSIOLOGY

Cardiac Output, Venous Return

and Their Regulation

Page 2: Physiology of Heart

Cardiac Output:

It is the quantity of blood pumped into the aorta each minute by the heart or the quantity of blood that flows through the circulation each minute.

Cardiac output = Heart Rate Stroke Volume

Venous return: It is the quantity of blood flowing from the veins into the right atrium each minute.

Venous Return = Cardiac Output

Page 3: Physiology of Heart
Page 4: Physiology of Heart

Increase in Cardiac Output The factors which increases the cardiac output are: Heart Venous Return Arterio-Venous Fistula Blood Volume Mean Systematic Filling

Pressure

Page 5: Physiology of Heart

Metabolic Rate Exercise Rate Pathology Size of the body

(Cardiac Index) Person’s age

Page 6: Physiology of Heart

Role Of Frank-Starling Mechanism

Frank-Starling Law: It states that “ Within physiologic limits, the heart pumps all the blood that returns to it by the way of veins.” Increased Venous Return

Cardiac muscles stretches to greater length

Ventricular muscle contracts with greater force

Increased Cardiac Output

Page 7: Physiology of Heart

EFFECTS Stronger Contractions: Increased heart volume stretches muscles and causes stronger contraction.

Heart Rate: Stretch increases heart rate as well.

S-A Node:

Direct effect on rhythmicity of the node to increase heart rate as much as 10-15%.

Bainbridge Reflex: It gives reflexes to the vasomotor center and then back to the heart by the way of sympathetic nerves and vagi, increases the heart rate.

Page 8: Physiology of Heart

Cardiac Output RegulationThe venous return to

the heart is the sum of all the local blood

flows through all the individual tissue segments of the

peripheral circulation.At each increasing

level of work output during exercise, the oxygen consumption

and the cardiac output increase in parallel to

each other.To summarize, cardiac output is determined by the sum of all the various factors throughout the

body that control local blood flow. All the local blood flows summate

to form the venous return, and the heart automatically pumps this returning blood back into the

arteries to flow around the system again.

Page 9: Physiology of Heart
Page 10: Physiology of Heart

Relation of Cardiac Output and Stroke Volume

Stroke Volume: Volume of blood that is ejected by each ventricles during systole is called Stroke Volume Output.

As the stroke volume increases the cardiac output also increases.

Stroke Volume depends upon

1. End diastolic Volume

2. Contractility

Page 11: Physiology of Heart

Limitations For The Cardiac OutputThere are definite limits to the amount of

blood that the heart can pump, which is expressed quantitatively in the form of cardiac output curves.

Normal: The plateau level of this normal cardiac output

curve is about 13 L/min. Hypoeffective: The lowermost curves are for hypoeffective hearts that are pumping at levels below normal. Hypereffective heart plateau – 5 L/min

Hypereffective: The uppermost curves are for Hypereffective hearts that are pumping better than normal. Hypoeffective heart plateau – 20 L/min

Page 12: Physiology of Heart

Hypoeffective Heart In this the heart is pumping at a very slow

rate and the cardiac output decreases. Factors that can cause hypoeffectivity are following:

1. Increased Arterial Pressure

2. Inhibition of Nervous Excitation

3. Abnormal Heart Rhythm

4. Coronary Artery Blockage

5. Valvular Heart Disease

6. Congenital Heart Disease

7. Myocarditis

8. Cardiac Hypoxia

Page 13: Physiology of Heart

Hypereffective Heart In this the heart is pumping at a

high rate and the cardiac output increases.

Two type of factors can make the heart a better pump than normal:

1. Nervous Stimulation: It involves Sympathetic Stimulation and Parasympathetic Inhibition.

2. Hypertrophy of The Heart Muscles: It involves the increased mass and contractile strength due to exercise and causing hypertrophy which allows increased Cardiac Output.

Page 14: Physiology of Heart

Pathologically High or Low Cardiac Output

In healthy humans, the average Cardiac Outputs are surprisingly constant from one person to another. However. Multiple clinical abnormalities can cause either high or low cardiac outputs.

Page 15: Physiology of Heart

High Cardiac Output High cardiac output is mostly caused

by reduced total peripheral Resistance.

Following are some of the conditions that can decrease the Peripheral Resistance and at the same time increase the Cardiac Output to above the normal.

1. Beriberi

2.Arteriovenous Fistula

3.Hyperthyroidism

4. Anemia

Page 16: Physiology of Heart

Low Cardiac Output

There are two factors that cause Low

Cardiac Output:

B. Abnormalities that cause the

Venous Return to fall too low

A. Abnormalities that cause pumping

effectiveness of the Heart to fall

too low

Page 17: Physiology of Heart

A. Cardiac Factors: Whenever the heart becomes severely damaged, regardless of the cause, its limited level of pumping may fall below that needed for adequate blood flow to the tissues. Some examples of this include:

1. Severe Coronary Blood

2. Myocardial Infarction

3. Severe Valvular Heart Disease

4. Myocarditis

5. Cardiac Temponade

6. Cardiac Metabolic Derangements

Page 18: Physiology of Heart

B. 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 Muscle Mass

5. Decreased Metabolic Rate

of the Tissues

Page 19: Physiology of Heart

THANK YOU

Page 20: Physiology of Heart

Any Questions???