Guyton and Hall Physiology Chapter 20 - Cardiac Output, Venous Return, and Their Regulation
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Questions and Answers

What happens to venous return when there is no pressure gradient?

  • Venous return remains unchanged
  • There is no venous return (correct)
  • Venous return becomes erratic
  • Venous return increases significantly

    • How does the filling level of the cardiovascular system affect blood flow into the heart?

  • High filling levels constrict blood flow
  • High filling levels ease blood flow (correct)
  • Filling levels have no effect on blood flow
  • Low filling levels enhance blood flow

    • Which physiological state represents a scenario where blood cannot return to the heart?

  • Increased right atrial pressure
  • Decreased systemic vascular resistance
  • Increased blood volume
  • Zero pressure gradient between vessels (correct)

    • What is a consequence of decreased filling in the cardiovascular system?

    <p>Blood flow into the heart becomes more difficult</p> Signup and view all the answers

    What needs to occur for blood to flow from peripheral vessels back to the heart?

    <p>A pressure difference between peripheral vessels and the right atrium</p> Signup and view all the answers

    What is the maximum increase in cardiac output that can occur due to nervous excitation and hypertrophy in athletes?

    <p>30 to 40 L/min</p> Signup and view all the answers

    What happens to venous return before the heart becomes a limiting factor?

    <p>It increases beyond 2.5 times the normal level.</p> Signup and view all the answers

    What characterizes a hypoeffective heart?

    <p>It pumps blood below normal levels.</p> Signup and view all the answers

    Which of the following is NOT a factor that can make the heart stronger than normal?

    <p>Hypotension</p> Signup and view all the answers

    What is one of the most important consequences of an increased pumping capacity in athletes?

    <p>Improved running time</p> Signup and view all the answers

    Which condition leads to hypoeffectivity of the heart?

    <p>Decreased heart muscle efficiency</p> Signup and view all the answers

    What mechanism primarily contributes to the heart's increased effectiveness in pumping for athletes?

    <p>Nervous excitation</p> Signup and view all the answers

    What is meant by a hypereffective heart?

    <p>A heart that is pumping better than normal.</p> Signup and view all the answers

    What effect does hypertrophy have on the heart?

    <p>Increases the strength of the heart's pumping ability.</p> Signup and view all the answers

    What is the primary effect of increased venous return on cardiac output?

    <p>It allows for much greater cardiac output.</p> Signup and view all the answers

    What primarily controls cardiac output under normal unstressed conditions?

    <p>Peripheral factors affecting venous return</p> Signup and view all the answers

    When does the heart become the limiting factor in determining cardiac output?

    <p>When the metabolic needs exceed cardiac capacity</p> Signup and view all the answers

    Which of the following accurately describes cardiac index?

    <p>Cardiac output per square meter of surface area</p> Signup and view all the answers

    What is the relationship between cardiac output and venous return under normal conditions?

    <p>Cardiac output equals venous return</p> Signup and view all the answers

    What happens to cardiac output when the heart is severely weakened?

    <p>It becomes limited by the heart's pumping ability</p> Signup and view all the answers

    Which statement best describes the role of metabolic needs in cardiac output determination?

    <p>It mainly controls cardiac output when venous return exceeds heart capacity</p> Signup and view all the answers

    Which component is NOT considered a determinant of cardiac output?

    <p>Temperature of the body</p> Signup and view all the answers

    How does venous return influence cardiac output under most normal conditions?

    <p>It directly determines cardiac output</p> Signup and view all the answers

    What happens when cardiac output falls below the necessary level for tissue nutrition?

    <p>The person experiences circulatory shock.</p> Signup and view all the answers

    How does positive-pressure breathing affect the cardiac output curve?

    <p>It shifts the curve to the right.</p> Signup and view all the answers

    What is the effect of opening the thoracic cage on intrapleural pressure?

    <p>It sets intrapleural pressure to 0 mm Hg.</p> Signup and view all the answers

    What condition occurs due to accumulation of fluid in the pericardial cavity?

    <p>Cardiac tamponade.</p> Signup and view all the answers

    What can shift the cardiac output curve to the right by 4 mm Hg?

    <p>Opening the thoracic cage.</p> Signup and view all the answers

    During which condition might one expect a significant shift in the cardiac output curve due to external pressure?

    <p>Cardiac tamponade.</p> Signup and view all the answers

    Which physiological state may lead to lethal circulatory shock within minutes?

    <p>Low cardiac output.</p> Signup and view all the answers

    What is a characteristic effect of strenuous breathing on blood pressure variations?

    <p>Dramatic variations of ±50 mm Hg.</p> Signup and view all the answers

    What general condition causes the need for a complex quantitative analysis of cardiac output regulation?

    <p>Extreme states of exercise.</p> Signup and view all the answers

    What is typically inadequate in cases of low cardiac output leading to circulatory shock?

    <p>Tissue perfusion.</p> Signup and view all the answers

    What effect does decreased skeletal muscle mass have on cardiac output?

    <p>It reduces cardiac output.</p> Signup and view all the answers

    Which factor requires an additional increase in right atrial pressure to maintain cardiac output with increased external pressure on the heart?

    <p>Increased intrapleural pressure.</p> Signup and view all the answers

    What is the result of a decreased metabolic rate in tissues like skeletal muscle?

    <p>Decreased blood flow and oxygen consumption.</p> Signup and view all the answers

    What type of changes in intrapleural pressure occur during respiration?

    <p>Cyclical changes.</p> Signup and view all the answers

    How much additional right atrial pressure is required to overcome a +2 mm Hg intrapleural pressure?

    <p>6 mm Hg.</p> Signup and view all the answers

    What physiological condition is likely to increase tissue blood flow?

    <p>Increased metabolic activity.</p> Signup and view all the answers

    What happens to the cardiac output curve with a decreased metabolic rate?

    <p>It shifts right.</p> Signup and view all the answers

    What is the normal right atrial pressure before any external factors are considered?

    <p>-4 mm Hg.</p> Signup and view all the answers

    Which of the following conditions is associated with a reduced metabolic rate in tissues?

    <p>Hypothyroidism.</p> Signup and view all the answers

    What is a likely consequence of prolonged periods of physical inactivity?

    <p>Decreased tissue oxygen needs.</p> Signup and view all the answers

    What condition is primarily associated with the heart being able to pump significantly more than normal?

    <p>Nervous stimulation and hypertrophy</p> Signup and view all the answers

    Which factor contributes to a hypoeffective heart?

    <p>Reduced blood volume returning to the heart</p> Signup and view all the answers

    What is the possible cardiac output level for an athlete with a hypereffective heart?

    <p>30-40 L/min</p> Signup and view all the answers

    What is a key factor that limits the heart's ability to increase cardiac output?

    <p>Decreased venous return</p> Signup and view all the answers

    Which of the following accurately reflects the relationship between venous return and cardiac output under normal conditions?

    <p>Increased venous return can enhance cardiac output.</p> Signup and view all the answers

    What causes abnormally high cardiac output according to the provided conditions?

    <p>Chronically reduced total peripheral resistance</p> Signup and view all the answers

    Which disease is specifically mentioned as being caused by a deficiency in thiamine?

    <p>Beriberi</p> Signup and view all the answers

    What is a significant physiological consequence of thiamine deficiency in relation to blood flow?

    <p>Compensatory peripheral vasodilation</p> Signup and view all the answers

    Which of the following statements best describes the relationship between cardiac output and peripheral resistance?

    <p>Decreased peripheral resistance can lead to increased cardiac output</p> Signup and view all the answers

    What feature distinguishes conditions related to high cardiac output from those that do not?

    <p>Chronically reduced total peripheral resistance</p> Signup and view all the answers

    What occurs as a result of a significant reduction in total peripheral resistance?

    <p>Increased venous return</p> Signup and view all the answers

    What is the primary effect of hyperthyroidism on metabolism?

    <p>Greatly increased metabolic activity</p> Signup and view all the answers

    What physiological change is associated with the presence of an arteriovenous (AV) fistula?

    <p>Direct blood flow from artery to vein</p> Signup and view all the answers

    What causes the arterial pressure to fall when pressure control is not maintained?

    <p>Uncontrolled cardiac output</p> Signup and view all the answers

    When total peripheral resistance decreases to half of normal levels, what is the expected impact on venous return and cardiac output?

    <p>Both may increase to twice the normal value</p> Signup and view all the answers

    What outcome is seen with the metabolic stimulant dinitrophenol without pressure control?

    <p>An insignificant increase in cardiac output</p> Signup and view all the answers

    What is one potential consequence of cardiac tamponade?

    <p>Decreased cardiac output</p> Signup and view all the answers

    Which of the following factors may contribute to increased venous return in specific conditions?

    <p>Presence of an AV shunt</p> Signup and view all the answers

    Which condition is characterized by an increase in blood flow to tissues?

    <p>Arteriovenous (AV) fistula</p> Signup and view all the answers

    What is the relationship between total peripheral resistance and cardiac output?

    <p>Inversely proportional</p> Signup and view all the answers

    Cardiac output is the total volume of blood the heart pumps in a minute, expressed in L/min.

    <p>True</p> Signup and view all the answers

    Oxygen consumption is not influenced by the amount of blood flow through individual tissue segments.

    <p>False</p> Signup and view all the answers

    The sum of all local blood flow regulations contributes to cardiac output regulation.

    <p>True</p> Signup and view all the answers

    Acute venous dilation most often results when the sympathetic nervous system suddenly becomes active.

    <p>False</p> Signup and view all the answers

    Low cardiac output can occur due to conditions that decrease the pumping effectiveness of the heart.

    <p>True</p> Signup and view all the answers

    Venous return is independent of local blood flow in peripheral circulation.

    <p>False</p> Signup and view all the answers

    Cardiac index is defined as cardiac output divided by body surface area.

    <p>True</p> Signup and view all the answers

    Blood pools in the vessels when their filling pressure becomes too high.

    <p>False</p> Signup and view all the answers

    Fainting is often a result of a sudden increase in sympathetic nervous system activity.

    <p>False</p> Signup and view all the answers

    Decreased cardiac output can lead to inadequate blood flow to bodily tissues.

    <p>True</p> Signup and view all the answers

    An additional set of curves is required to show the effect on cardiac output caused by changing external pressures on the outside of the heart.

    <p>True</p> Signup and view all the answers

    Changes in external pressures have no effect on cardiac output.

    <p>False</p> Signup and view all the answers

    The effect of pleural pressure on cardiac output is negligible.

    <p>False</p> Signup and view all the answers

    Cardiac output is solely dependent on the internal mechanisms of the heart and does not require considerations of external pressures.

    <p>False</p> Signup and view all the answers

    Understanding external pressures on the heart is critical for analyzing cardiac function.

    <p>True</p> Signup and view all the answers

    The relationship between cardiac output and external pressures is irrelevant to overall cardiovascular health.

    <p>False</p> Signup and view all the answers

    Curves illustrating the effect of external pressure are less important than those showing internal heart pressures.

    <p>False</p> Signup and view all the answers

    An increase in external pressure on the heart may require an adjustment in cardiac output.

    <p>True</p> Signup and view all the answers

    The pleural pressure directly impacts the heart but does not influence venous return.

    <p>False</p> Signup and view all the answers

    Curves required to represent cardiac output are irrelevant to the discussion of external pressures.

    <p>False</p> Signup and view all the answers

    Match the heart conditions with their descriptions:

    <p>Hypoeffective heart = Reduced ability to pump blood Hypereffective heart = Increased ability to pump blood Increased heart rate = Up to 180 to 200 beats/min Increased contractility = Pumping strength doubles</p> Signup and view all the answers

    Match the effects of nervous excitation on cardiac output:

    <p>Increase in heart rate = Can reach 180 to 200 beats/min Increase in contractility = Strength of contraction doubles Sympathetic stimulation = Enhances heart pumping effectiveness Parasympathetic inhibition = Pauses heart's inhibitory signals</p> Signup and view all the answers

    Match the terms related to cardiac output regulation:

    <p>Total peripheral resistance = Reciprocal relationship with cardiac output Cardiac output = Blood volume ejected by the heart Long-term resistance changes = Affects cardiac output inversely Arterial pressure = Pressure exerted by circulating blood</p> Signup and view all the answers

    Match the cardiovascular elements with their functions:

    <p>Heart rate = Frequency of heartbeats Contractility = Strength of heart muscle contractions Cardiac output = Amount of blood pumped in a minute Peripheral resistance = Opposition to blood flow in vessels</p> Signup and view all the answers

    Match the physiological concepts with their effects:

    <p>Increased venous return = Boosts cardiac output Sympathetic stimulation = Increases heart pumping effectiveness Long-term high resistance = Reduces cardiac output Physical inactivity = Can lead to decreased cardiac efficiency</p> Signup and view all the answers

    Match the following factors with their effects on the heart's ability to pump blood:

    <p>Severe Hypertension = Decreases cardiac output Autonomic Nervous System Activity = Increases heart rate and contractility Venous Return Increase = Improves cardiac output Total Peripheral Resistance Decrease = May lower arterial pressure</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Cardiac Output = The volume of blood the heart pumps per minute Vein Constriction = Reduces blood return to the heart Muscle Arterioles Relaxation = Increases blood flow to active muscles Hypertrophy = Enlargement of heart muscle fibers</p> Signup and view all the answers

    Match the following physiological conditions with their outcomes:

    <p>Increased Metabolism During Exercise = Causes muscle arterioles to relax Nervous System Excitation = Compensates arterial pressure drops Decreased Filling = Leads to lower cardiac output Peripheral Tissues Dilating = Increases venous return</p> Signup and view all the answers

    Match the following changes with their impacts on cardiovascular function:

    <p>Increased Heart Rate = Enhances cardiac output Increased Contractility = Improves blood pumping efficiency Peripheral Vasodilation = Increases venous return Decreased Total Peripheral Resistance = Allows better blood flow during exercise</p> Signup and view all the answers

    Match the following cardiovascular responses with the associated triggers:

    <p>Blood Vessel Constriction = Triggered by nervous system signals Increased Oxygen Demand = Occurs during physical activity Arterial Pressure Compensation = Occurs during significant metabolic changes Skeletal Muscle Contraction = Decreases total peripheral resistance</p> Signup and view all the answers

    Study Notes

    Cardiac Output Regulation

    • Cardiac output is the amount of blood pumped by the heart per minute.
    • Venous return is the amount of blood returning to the heart per minute.
    • Venous return increases up to 2.5 times the normal level before the heart becomes the limiting factor in cardiac output.
    • When the heart pumps at levels above normal this is known as a hypereffective heart.
    • When the heart pumps at levels below normal this is known as a hypoeffective heart.

    Factors That Cause a Hypereffective Heart

    • Increased nervous stimulation
    • Hypertrophy, including marathon runners, can increase cardiac output to 30–40 L/min.

    Factors That Cause a Hypoeffective Heart

    • Factors that reduce the heart’s ability to pump blood
    • Decreasing arterial pressure, which is usually maintained by nervous reflexes, can decrease cardiac output.

    High Cardiac Output Caused by Reduced Total Peripheral Resistance

    • Beriberi
      • A disease caused by a lack of thiamine (vitamin B1).
      • It can decrease total peripheral resistance by up to 50%.
      • Venous return and cardiac output can increase to twice the normal value.
    • Arteriovenous fistula
      • A fistula (also called an AV shunt) is a direct connection between an artery and a vein.
      • This connection causes a decrease in total peripheral resistance and therefore increased venous return and cardiac output.
    • Hyperthyroidism
      • Increased metabolism in hyperthyroidism results in increased circulatory blood flow.

    Low Cardiac Output

    • Decreasing total peripheral resistance can lead to reduced blood flow.
    • Conditions that can affect the heart and cause low cardiac output:
      • Myocardial infarction
      • Congestive heart failure
      • Pulmonary embolism
      • Cardiac tamponade
      • Cardiac metabolic derangements

    Circulatory Shock

    • Cardiac output falling below the minimum level required for adequate tissue nutrition leads to circulatory shock.

    Mean Circulatory Filling Pressure (MCFP)

    • The MCFP is the average pressure throughout the systemic circulation when blood flow is stopped.
    • The MCFP is nearly equal to the mean systemic filling pressure.
    • MCFP is not readily measurable in a live animal.
    • Factors that shift the MCFP:
      • Increased sympathetic nervous stimulation
      • Changes in total blood volume

    Venous Return Curve

    • Factors that shift the venous return curve:
      • Positive-pressure breathing
      • Negative-pressure breathing
      • Opening of the thoracic cage
      • Cardiac tamponade

    Cardiac Output and Tissue Metabolism

    • Cardiac output is the sum of all tissue blood flow
    • Most local blood flow is regulated by tissue metabolism

    Local Blood Flow Regulation

    • Venous return to the heart is the sum of blood flow through all tissues in the circulation
    • Cardiac output regulation is the sum of all local blood flow regulations
    • Acute venous dilation can occur when the sympathetic nervous system is inactive
    • This leads to blood pooling in peripheral vessels and a decrease in venous return

    Decreased Cardiac Output

    • Conditions that lead to decreased cardiac output fall into two categories: decreased pumping effectiveness of the heart and decreased venous return
    • Cardiac factors that decrease output include heart damage, regardless of cause

    Effect of External Pressure on Cardiac Output

    • Changes in external cardiac pressure affect cardiac output curves
    • Normal intrapleural pressure is about -4mmHg
    • Increased intrapleural pressure leads to decreased cardiac output

    Venous Return and Cardiac Output

    • Venous return is the volume of blood returning to the heart per minute
    • Cardiac output is the volume of blood pumped by the heart per minute
    • Venous return determines cardiac output
    • Increased venous return leads to increased cardiac output

    Impact of Blood Volume on Cardiac Output

    • An increase in blood volume of about 20% increases cardiac output
    • This shifts the venous return curve to the right, increasing both venous return and cardiac output
    • Increased blood volume distends blood vessels, reducing resistance and further increasing cardiac output

    Cardiac Output

    • Cardiac output is the amount of blood pumped by the heart per minute.
    • Cardiac output is a measure of how efficiently the heart is pumping blood.
    • Cardiac output is influenced by both the strength of the heart's contraction and the heart rate.
    • Changes in total peripheral resistance (TPR) have a reciprocal relationship with cardiac output.

    Nervous System Regulation

    • The nervous system impacts the heart rate and contractility, which in turn influence cardiac output.
    • Sympathetic stimulation increases heart rate and contractility.
    • Parasympathetic inhibition also increases heart rate and contractility.
    • Heart rate and contractility are critical determinants of the heart's ability to pump blood.

    Factors Affecting Cardiac Output

    • High blood pressure (hypertension) can strain the heart.
    • Valvular heart disease can decrease the efficiency of the heart's pumping function.
    • Cardiac arrhythmias (irregular heartbeats) can impact the heart's pumping efficiency.
    • Pericarditis can affect the heart's ability to pump blood.
    • Myocardial disease can decrease the heart's ability to pump blood.

    Nervous System Regulation During Exercise

    • During exercise, muscles require more oxygen and nutrients.
    • The nervous system increases heart rate and contractility to ensure adequate blood flow to the muscles.
    • Arterioles in the contracting skeletal muscles dilate, reducing TPR.

    High Cardiac Output Caused by Reduced TPR

    • Beriberi, caused by thiamine deficiency, results in vasodilation and increased cardiac output.

    Cardiac Output Curves

    • Cardiac output curves illustrate the relationship between right atrial pressure and cardiac output.
    • The normal cardiac output curve shows a typical relationship between pressure and output.
    • Hypereffective hearts have higher maximum cardiac output, while hypoeffective hearts have lower cardiac output.
    • The position of the cardiac output curve can shift based on factors such as extracardiac pressure.

    Venous Return Curve

    • The venous return curve depicts the relationship between right atrial pressure and venous return.
    • This curve illustrates how blood flows back into the heart from the systemic circulation.
    • The equilibrium point on the venous return curve represents the normal right atrial pressure, cardiac output, and venous return.

    Effect of Increased Blood Volume

    • Increasing blood volume by 20% significantly increases cardiac output, initially due to elevated venous pressure and reduced TPR.
    • The increased blood volume distends blood vessels, further reducing TPR and increasing cardiac output.

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