Cardiac Output and Blood Flow in Muscle Tissues

Question 1

What is the definition of cardiac output?

Answer 1

Cardiac output is the volume of blood pumped by heart per minute.

Question 2

What is the definition of cardiac index?

Answer 2

Cardiac index is cardiac output to surface area of being.

Question 3

What is the cardiac index in a normal human being?

Answer 3

5 L/1.7 m² = 3 L/min/m²

body surface area=1.7 m²

cardiac output= 5 L

Question 4

What is the equation for cardiac index?

Answer 4

cardiac index= cardiac output/ body surface area

Question 5

What is the primary controller of cardiac output?

Answer 5

venous return. Most believe that the heart is the controller of cardiac output but if the blood is not returned then the heart cannot possibly pump blood

Question 6

Would an individual with a large body surface area or an individual with a smaller body surface area have the largest cardiac output?

Answer 6

The individual with a large body surface area would have the largest cardiac output because cardiac output has a direct relationship with body surface area.

Question 7

What does the peak in this graph indicate?

Answer 7

The peak in this graph indicates an increase in cadiac index to meet the demands of growth and increased activity at this age level.

Question 8

What does the slow drop off in this graph indicate?

Answer 8

The slow decrease in this graph indicates that after 10 years old there is a decrease of muscle mass and/or activity with age.

Question 9

What is the oxygen fick principle?

Answer 9

The oxygen fick principle is a technique to measure cardiac output noninvasively.

The diagram shows that there was 200 mL/L blood leaving the heart a minute and 160mL/L of blood returning the heart a minute. This means that every liter of blood going through the lungs absorbs 40mL of oxygen.

200mL/ 40mL = 5 - 1 liter portions that must pass through the lungs every minute to absorb this amount of oxygen

Question 10

What is the equation used in the Fick principle to calculate cardiac output?

Answer 10

cardiac output = O₂ consumption/ [0₂]_{pul vein}- [O₂]_{pul art}

Question 11

What is the determining factor that controls how much blood the heart pumps out?

Answer 11

the venous return determines how much blood the heart pumps out.

Question 12

True or false. All pressures in the systemic circuit are higher than the pulomonary circuit.

Answer 12

True

Question 13

True or False. Cardiac output and rate of the systemic circuit is greater than the pulmonary circuit.

Answer 13

False. The systemic and pulmonary circuit have equal cardiac output and rate because they are connected in series.

Question 14

Chemical composition of pulmonary venous blood is (different/similar) to that of systemic arterial blood.

Answer 14

Chemical composition of pulmonary venous blood is similar to that of systemic arterial blood.

Question 15

Chemical composition of venous blood entering the right atrium is (different/similar) to the composition of pulmonary arterial blood.

Answer 15

Chemical composition of venous blood entering the right atrium is the same as the composition of pulmonary arterial blood.

Question 16

What are 4 factors that directly affect cardiac output?

Answer 16

1. basic level of body metabolism
2. whether the person is exercising
3. age
4. size of body

Question 17

What are normal values of cadiac output for:

young, health male:

women:

resting adult:

Answer 17

young, health male: 5.6 L/min

women: 4.9 L/min

resting adult: 5.0 L/min

Question 18

What is the Frank-Starling Law?

Answer 18

The Frank Starling Law states that when there is an increase in blood pressure there is a stretch in the walls of heart chambers and as a reaction the heart muscles contract with increased force. Therefore, the blood that flows into the heart is automatically pumped without delay.

Question 19

What is the bainbridge reflex?

Answer 19

Bainbridge reflex (atrial stretch reflex) is a response to increased stretch of receptors in the right atrium causing the heart to pump faster.

Question 20

How does Beriberi effect cardiac output and peripheral resistance?

Answer 20

Lack of vitamine B1 causes diminished ability of the tissues to use some cellular nutrients, and the local tissue blood flow mechanisms in turn cause marked compensatory peripheral vasodilation and decreased peripheral resistance and increased cardiac output.

Question 21

How do AV (atriovenous) shunts affect cardiac output?

Answer 21

Atriovenous shunt is an abnormal bypass from an artery to a vein and when done in a major vessel can markedly decrease the peripheral resistance. As a long-term response the body increases cardiac output.

Question 22

what effect does hyperthyroidism have on cardiac output?

Answer 22

Hyperthyroidism is an over production and secretion of T3 adn T4. T3 in particular works to increase basal metabolic rate and, thus, increases the body’s oxygen and energy consumption by dilating vessels. This creates decreased peripheral resistance and over time and increased cardiac output. Notice that hypothyroidism is on the other side of the graph and has the opposite effect.

Question 23

What effect does anemia have on cardiac output?

Answer 23

Anemia is a deficiency of hemoglobin and as a result has a hard time delivering oxygen to tissue and the body will vasodilate to compensate. This vasodilation causes decreased peripheral resistance and over time increased cardiac output to keep the arterial pressure constant.

Question 24

What effect does pulmonary disease have on cardiac output?

Answer 24

Pulmonary disease is any condition in which it is difficult to breathe, blocks airflow, an therefore decrease of oxygen loading. As a result the body will compensate by vasodilating, causing decreased peripheral resistance and over time increased cardiac output to keep the arterial pressure constant.

Question 25

What effect does Paget’s disease have on cardiac output?

Answer 25

Paget’s disease is a condition of abnormal bone destruction and regrowth and sometimes these overgrowth of bones have extra blood vessels which decreases the peripheral resistance and the heart has to work harder to deliver blood by increasing the cardiac output. The arterial pressure must stay the same.

Question 26

How would limb amputations effect peripheral resistance and cardiac output?

Answer 26

(This example is a great analogy to electrical circuits). Limb amputations increase peripheral resistance (reducing the number of resistors in parallel increases total resistance). Over time the body would respond by decreasing cardiac output and keeping arterial pressure constant.

Question 27

How does hypothyroidism effect peripheral resistance and cardiac output?

Answer 27

Hypothyroidism is an underproduction of T3 and T4 and as a result there is a decrease in vasodilation because there isn’t as much T3 (increases basal metabolic rate, oxygen consumption, energy consumption). This decrease in vasodilation factors and its association with vasoconstrictors causes an increase in peripheral resistance and the cardiac output decreases over time and arterial pressure remains constant.

Question 28

What are 3 factors that cause a hypereffective heart?

Answer 28

1. overstimulation of sympathetic nervous system
2. hypertrophy of heart
3. exercise via the nervous system

Question 29

How does exercise cause a hypereffective heart?

Answer 29

• increased metabolism= relax arterioles= more blood to arterioles
• brain signals to muscles to excite circulatory activity
• causes large vein constriction = reduced compliance= increased venous return
• increased heart rate and increased contractility of the heart.

Question 30

What are 7 factors that cause a hypoeffective heart?

Answer 30

1. increased arterial pressure
2. inhibition of nervous excitation of the heart
3. pathological factors causing abnormal heart rhythm/rate
4. coronary artery blockage
5. valvular heart disease
6. congenital heart disease
7. cardiac hypoxia

Question 31

What does the plateau in this graph indicate?

Answer 31

The plateau in this graph shows that when the right atrial pressure continues to increase it will hit a certain point where the cardiac output will no longer increase (this is the max that the heart is capable of pumping). The rapid increase of cardiac output reflects how blood is flowing back to the right atrium.

This graph also shows that a normal heart is capable of pumping 2.5 times (13.5L/min) the normal cardiac output(5L/min).

Question 32

What are 5 factors causing decreased cardiac output?

Answer 32

1. severe blood vessel blockage –> myocardial infarction
2. severe valvular disease
3. myocarditis
4. cardiac tamponade
5. cardiac metabolic derangements

Question 33

what are 5 (non-cardiac) factors that cause decreased cardiac output?

Answer 33

1. decreased blood volume
2. acute venous dilation
3. obstruction of large veins
4. decreased tissue mass
5. decreased metabolic rate of tissues

Question 34

What is the effect of dinitrophenol (DNP)?

Answer 34

dinitrophenol is a metabolic stimulant which causes vasodilation.

Question 35

What does this graph show about nervous control on cardiac output and arterial pressure?

Answer 35

Administration of DNP to a dog with nervous control caused vasodilation and increased in cardiac output, however there was no change in arterial pressure.

When DNP was administered to a dog with no nervous control, it caused vasodilation but cardiac output did not increase (lack of nervous control) and as a result arterial pressure decreased.

Question 36

What factors affect venous return to the heart from systemic circulation?

Answer 36

1. right atrial pressure
2. degree of filling of systemic circulation
3. pressure gradient for venous return
4. resistance to blood flow

Question 37

How does right atrial pressure affect venous return?

Answer 37

Right atrial pressure exerts a force backwards and impedes flow. Mean systemic filling pressure = +7mmHg. So when right atrial pressure= +7mmHg then venous return = 0

When right atrial pressure = -2mmHg the venous return reaches a plateau (this negative pressure is caused by a collapsed vein entering chest.

Question 38

What affect does -2mmHg right atrial pressure have on venous return?

Answer 38

-2mmHg right atrial pressure causes the venous return to hits its max. This is the plateau and there will be no diference in venous return in right atrial pressures lower than this.

The negative right atrial pressure is caused by collapse of veins entering chest.

Question 39

How does degree of filling of systemic circulation effect the venous return?

Answer 39

Increasing the volume of blood in circulatory system increases the mean circulatory filling pressure (static pressure;no heart pumping)

When blood volume is 5L; mean circulatory filling pressure = 7 mmHg

this almost equals mean systemic filling pressure

when blood volume = 4 L; mean circulatory filling pressure = 0mmHg

The greater the difference between the mean systemic filling pressure and the right atrial pressure, the greater the venous return.

Question 40

What is the pressure gradient for venous return?

Answer 40

pressure gradient for venous return = difference between the mean systemic filling pressure and the right atrial pressure

Question 41

What is the equation for calculating venous return?

Answer 41

venous return= (mean systemic filling pressure)-(right atrial pressure)/(resistance to venous return)

Question 42

What are 3 factors that affect venous return?

Answer 42

1. right atrial pressure
2. mean systemic filling pressure (Psf)
3. blood flow resistance between peripheral vessels and right atrium

Question 43

At what pressure value is there a plateau in venous return?

Answer 43

No matter what the mean systemic filling pressure is, there is always a plateau at -2mmHg and is caused by the right atrial pressure dropping below atmospheric pressure and the large vessels entering chest collapsing.

Question 44

What is the difference between mean systemic filling pressure and mean circulatory filling pressure?

Answer 44

Mean circulatory filling pressue is measured by stopping the heart, clamping the large vessels to the heart, and measuring pressures of the systemic circulation independent from the pulmonary circulation.

Mean systemic filling pressure is almost the same since the pulmonary circulatory system has less than one eighth the capacitance.

Question 45

what effect does resistance have on venous return?

Answer 45

A decrease in resistance allows more blood to flow and has a higher venous return, while increased resistance causes decreased venous return.

Question 46

What is the highest level to which the right atrial pressure can rise to?

Answer 46

The right atrial pressure can only rise to its max which is equal to the mean systemic filling pressure.

Question 47

What effect does a 20% increase in blood volume have on venous return, cardiac output, and atrial pressure?

Answer 47

A 20% increase in blood volume causes the vessels to be distended and decrease in vascular resistance. This decreased vascular resistance allows an increase in venous return, and increase in atrial pressure and cardiac output.

Question 48

What effect does a decrease in blood volume have on venous return, cardiac output, and atrial pressure?

Answer 48

A decrease in blood volume would cause an increase in vascular resistance and a decrease in mean systemic pressure and is reflected by a shift of the vascular function curve to the left. Both cardiac output and atrial pressure are decreased.

An example that would cause a decrease in blood volume is hemorrhage or increase in venous capacitance.

Question 49

What are 4 mechanisms that can decrease venous compliance?

Answer 49

1. sympathetic stimulation
2. muscle pump
3. exercise
4. lying down

Question 50

What is Psf and what are two ways you can increase Psf?

Answer 50

Psf is the mean systemic filling pressure. You can increase this by increase vascular volume or decrease venous compliance.

Question 51

Increased Psf has what effect on cardiac output?

Answer 51

when Psf increases, cardiac output increases because more blood is returned to the heart.

Question 52

What are two ways you can decrease Psf?

Answer 52

1. decrease vascular volume (blood volume)
2. increase venous compliance

Question 53

What are 4 mechanisms that increase venous compliance?

Answer 53

1. inhibit sympathetics (vasodilation)
2. alpha block (vasodilation)
3. venodilators
4. standing upright (blood pools in legs)

Question 54

What are 4 mechanisms that decrease vascular volume?

Answer 54

1. hemorrhage
2. burn trauma
3. vomiting (fluid loss)
4. diarrhea (fluid loss)

Question 55

What are two sympathetic effects on the circulatory system?

Answer 55

• makes the heart a stronger pump
• increases the Psf by increasing contraction of peripheral vessels and increases resistance and venous return.