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

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Questions and Answers

What is the normal value of intrapleural pressure?

  • +4 mm Hg
  • 0 mm Hg
  • -4 mm Hg (correct)
  • -2 mm Hg

    • How does an increase in intrapleural pressure affect cardiac output?

  • It has no effect on cardiac output
  • It decreases cardiac output (correct)
  • It increases cardiac output
  • It doubles cardiac output

    • What is the primary mechanism by which cardiac tamponade affects cardiac output?

  • Decreased vascular resistance
  • Increased heart rate
  • Increased preload
  • Decreased stroke volume (correct)

    • Which of the following is true regarding external pressure's effect on vascular return?

    <p>Increased external pressure decreases venous return.</p> Signup and view all the answers

    What effect does a pressure of -4 mm Hg have on the cardiac output curve?

    <p>It creates a parallel shift upwards.</p> Signup and view all the answers

    What happens to the cardiac output curve when intrapleural pressure is increased to -2 mm Hg?

    <p>It demonstrates marked reduction in cardiac output.</p> Signup and view all the answers

    Which factor primarily contributes to changes in venous return as depicted by cardiac output curves?

    <p>Intrapleural pressure</p> Signup and view all the answers

    What does an increase in external pressure typically indicate in terms of cardiac tamponade conditions?

    <p>Reduced cardiac efficiency</p> Signup and view all the answers

    What is the condition called when cardiac output falls so low that nutritional deficiency occurs in tissues?

    <p>Cardiac Shock</p> Signup and view all the answers

    What happens to total peripheral resistance when vasodilator products are released from tissues?

    <p>It decreases markedly.</p> Signup and view all the answers

    Which of the following factors can lead to decreased venous return?

    <p>Decreased blood volume</p> Signup and view all the answers

    How does anemia affect peripheral resistance and cardiac output?

    <p>Decreases total peripheral resistance.</p> Signup and view all the answers

    In the context of increased cardiac output, what can contribute to an increase of 40% to 80% above normal?

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

    What causes acute venous dilation most often?

    <p>Sudden loss of sympathetic nervous system activity</p> Signup and view all the answers

    Which of the following conditions can lead to abnormally low cardiac output?

    <p>Heart damage</p> Signup and view all the answers

    What is a primary consequence of decreased venous return?

    <p>Flaccid peripheral blood vessels</p> Signup and view all the answers

    How does blood pooling occur in the vessels?

    <p>Dilation of peripheral capacitance vessels</p> Signup and view all the answers

    Which phenomenon can result from low cardiac output due to cardiac factors?

    <p>Catastrophic hypotension</p> Signup and view all the answers

    What effect does the dilation of peripheral veins have on vascular filling pressure?

    <p>It decreases markedly</p> Signup and view all the answers

    What is the relationship between sympathetic nervous system activity and venous return?

    <p>Increased activity enhances venous constriction</p> Signup and view all the answers

    Which of the following could indicate cardiac tamponade?

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

    Which statement is true regarding pressure-volume relationships in low cardiac output scenarios?

    <p>Poor contractility reduces stroke volume and alters pressure-volume dynamics</p> Signup and view all the answers

    What condition is described when cardiac output falls below the required level for adequate tissue nutrition?

    <p>Circulatory shock</p> Signup and view all the answers

    How can positive-pressure breathing affect cardiac output curves?

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

    What physiological change occurs during the opening of the thoracic cage related to intrapleural pressure?

    <p>Intrapleural pressure increases to 0 mm Hg.</p> Signup and view all the answers

    In the context of cardiac output regulation, what does accumulation of fluid in the pericardial cavity indicate?

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

    What can cause the cardiac output curves to shift farther to the right during stressful situations?

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

    How does breathing against negative pressure affect right atrial pressure?

    <p>It shifts right atrial pressure to a more negative value.</p> Signup and view all the answers

    Which factor is not associated with the regulation of cardiac output in normal conditions?

    <p>High external cardiac pressure.</p> Signup and view all the answers

    What major risk is associated with circulatory shock?

    <p>Potentially lethal outcomes.</p> Signup and view all the answers

    What is the primary effect of decreased cardiac output on tissue nutrition?

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

    Which situation would lead to a more complex quantitative analysis of cardiac output regulation?

    <p>Extreme physical stress.</p> Signup and view all the answers

    What is the normal value for cardiac output indicated at the equilibrium point?

    <p>5 L/min</p> Signup and view all the answers

    An increase in blood volume by 20% results in what effect on cardiac output?

    <p>Increases cardiac output to about 2.5 to 3 times normal</p> Signup and view all the answers

    What happens to the right atrial pressure as blood volume increases?

    <p>It increases from 0 to 16 mm Hg</p> Signup and view all the answers

    How does increased blood volume affect resistance in blood vessels?

    <p>Reduces resistance due to vessel distension</p> Signup and view all the answers

    At the equilibrium point, what value corresponds to the right atrial pressure?

    <p>0 mm Hg</p> Signup and view all the answers

    What characterizes the effect of increased venous return on cardiac output?

    <p>Enhances myocardial contractility</p> Signup and view all the answers

    What is the equilibrium point's role in venous return regulation?

    <p>It balances cardiac output and venous return</p> Signup and view all the answers

    When blood volumes are infused, which pressure values will most likely change?

    <p>Both right atrial pressure and cardiac output will change</p> Signup and view all the answers

    What is likely to occur when there is cardiac tamponade?

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

    How is the relationship between pressure and volume reflected during venous return?

    <p>Pressure increases with increasing volume until a threshold</p> Signup and view all the answers

    What happens to cardiac output when total peripheral resistance decreases and arterial pressure remains unchanged?

    <p>Cardiac output increases</p> Signup and view all the answers

    Which statement accurately summarizes the relationship between oxygen consumption and blood flow during exercise?

    <p>Blood flow rises proportionately with increasing oxygen consumption</p> Signup and view all the answers

    What primarily determines the long-term level of cardiac output?

    <p>The balance of peripheral vascular resistance and local blood flow factors</p> Signup and view all the answers

    What occurs to cardiac output when total peripheral resistance is exactly normal?

    <p>Cardiac output meets normal physiological levels</p> Signup and view all the answers

    Which factor does NOT directly influence the regulation of cardiac output under normal conditions?

    <p>External atmospheric pressure</p> Signup and view all the answers

    Which condition can lead to obstruction of the large veins leading into the heart?

    <p>Severe valvular heart disease</p> Signup and view all the answers

    What is a consequence of obstruction in the large veins leading to the heart?

    <p>Marked decrease in cardiac output</p> Signup and view all the answers

    Which condition is associated with a significant impact on cardiac output as illustrated in the provided data?

    <p>Severe valve disease</p> Signup and view all the answers

    Which of the following conditions would likely NOT contribute to low cardiac output as per the examples provided?

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

    Which factor would most directly cascade into increased difficulty for cardiac output based on the data presented?

    <p>Obstruction of large veins</p> Signup and view all the answers

    What condition occurs when cardiac output falls below levels required for adequate tissue nutrition?

    <p>Circulatory shock</p> Signup and view all the answers

    What effect does positive-pressure breathing have on the cardiac output curve?

    <p>Shifts the curve to the right</p> Signup and view all the answers

    How does breathing against negative pressure affect right atrial pressure?

    <p>Shifts it to a more negative value</p> Signup and view all the answers

    In which scenario would you expect a complex quantitative analysis of cardiac output regulation to be necessary?

    <p>During acute circulatory shock</p> Signup and view all the answers

    What impact does cardiac tamponade have on cardiac output curves?

    <p>Shifts the curve to the right due to increased external pressure</p> Signup and view all the answers

    What happens to intrapleural pressure during the opening of the thoracic cage?

    <p>Decreases to 0 mm Hg</p> Signup and view all the answers

    Which of the following factors is not related to the regulation of cardiac output under normal conditions?

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

    What is a significant risk associated with prolonged circulatory shock?

    <p>Organ failure</p> Signup and view all the answers

    What effect does the accumulation of fluid in the pericardial cavity indicate?

    <p>External cardiac pressure rise</p> Signup and view all the answers

    Which statement is true regarding circulatory changes during strenuous breathing?

    <p>Variations in pressure can reach ±50 mm Hg</p> Signup and view all the answers

    Hyperthyroidism is categorized as a hypoeffective condition in terms of cardiac output.

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

    Anemia reduces cardiac output but does not affect total peripheral resistance.

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

    An increase in total peripheral resistance results in an increase in cardiac output.

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

    Both arms and legs removal has no impact on arterial pressure or cardiac output.

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

    The heart rate can increase from 72 beats/min to as high as 200 beats/min under sympathetic stimulation.

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

    Increased contractility means the heart can pump with less strength than normal.

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

    The normal level of cardiac output is identified as 15 L/min.

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

    Paget's disease affects cardiac output by increasing total peripheral resistance.

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

    Nervous excitation reduces the pumping effectiveness of the heart.

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

    The relationship between cardiac output and total peripheral resistance is inversely proportional.

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

    Acute venous dilation occurs most often due to increased sympathetic nervous system activity.

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

    Low cardiac output can result from conditions that either decrease the heart's pumping effectiveness or decrease venous return.

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

    Blood pooling in the vessels occurs when the heart is pumping effectively.

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

    Fainting is often a result of sudden loss of parasympathetic nervous system activity.

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

    When cardiac output is low, the heart can still maintain adequate blood flow to the tissues.

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

    The dilation of peripheral veins decreases the filling pressure of the vascular system.

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

    Venous return is increased when blood vessels become markedly dilated.

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

    The primary consequence of decreased cardiac output is increased oxygen delivery to tissues.

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

    Certain cardiac conditions can lead to decreased pumping effectiveness of the heart.

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

    Sudden loss of sympathetic nervous system activity leads to constriction of peripheral blood vessels.

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

    Match the following factors with their effect on heart performance:

    <p>Nervous stimulation = Hypereffective heart Hypertrophy = Hypereffective heart Decreased blood ability = Hypoeffective heart Obstruction of veins = Hypoeffective heart</p> Signup and view all the answers

    Match the following descriptions with their corresponding heart conditions:

    <p>Pumping better than normal = Hypereffective heart Pumping at levels below normal = Hypoeffective heart Allowing heart to pump 30 to 40 L/min = Hypereffective heart Decreased cardiac output = Hypoeffective heart</p> Signup and view all the answers

    Match the following physiological effects with their descriptions:

    <p>Increased venous return = Higher cardiac output Nervous excitation = Enhanced heart performance Hypertrophy from training = Stronger heart pump Reduction in heart pump ability = Hypoeffective heart</p> Signup and view all the answers

    Match the following cardiac output characteristics with their causes:

    <p>Higher than normal pumping levels = Nervous stimulation and hypertrophy Cardiac output below normal = Factors decreasing pumping ability Extreme heart efficiency = Athletic training effects Impaired venous return = Obstruction and fluid accumulation</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Hypereffective heart = Heart pumping significantly above normal Hypoeffective heart = Heart pumping below normal levels Venous return = Blood returning to the heart Cardiac output = Volume of blood pumped by the heart per minute</p> Signup and view all the answers

    Match the following terms related to cardiac output with their definitions:

    <p>Cardiac Output = The amount of blood the heart pumps in a given time period Venous Return = The flow of blood back to the heart Cardiac Index = Cardiac output adjusted for body surface area Peripheral Resistance = The resistance to blood flow in the circulatory system</p> Signup and view all the answers

    Match the following factors affecting cardiac output with their influence:

    <p>Metabolic Needs = Increase cardiac output Cardiac Tamponade = Decrease cardiac output Increased Blood Volume = Increase venous return Peripheral Vein Dilation = Decrease vascular filling pressure</p> Signup and view all the answers

    Match the following conditions with their effect on cardiac output:

    <p>Anemia = Decreases peripheral resistance Heart Weakness = Limits cardiac output Fluid Accumulation in Pericardial Cavity = Interferes with heart function Obstruction in Large Veins = Reduces venous return</p> Signup and view all the answers

    Match the following physiological terms with their correct association:

    <p>Equilibrium Point = Balance between cardiac output and venous return Negative Pressure Breathing = Can enhance venous return Intrapleural Pressure = Affects cardiac output indirectly Total Peripheral Resistance = Influences flow through the circulatory system</p> Signup and view all the answers

    Match the following cardiovascular features with their characteristics:

    <p>Cardiac Output Regulation = Controlled mainly by metabolic demands High Cardiac Output = Often seen during exercise Low Cardiac Output = Can lead to tissue nutritional deficiency Increased Right Atrial Pressure = Occurs with high blood volume</p> Signup and view all the answers

    Study Notes

    Effects of External Pressure on Cardiac Output Curves

    • Intrapleural pressure, the pressure within the chest cavity, normally sits around -4 mmHg.
    • Increases in intrapleural pressure, such as during deep breaths or positive-pressure breathing, shift the cardiac output curve to the right.
    • Cardiac tamponade, the buildup of fluid around the heart, also raises external pressure and shifts the curve to the right.

    Cardiac Output Regulation

    • Cardiac output is the amount of blood pumped by the heart each minute.
    • Several factors influence cardiac output regulation, including heart pumping efficiency and venous return (blood returning to the heart).
    • If cardiac output falls below the level needed for adequate tissue nutrition it is considered circulatory shock.

    Factors Affecting Venous Return

    • Venous return is the flow of blood back to the heart.
    • Several factors affect venous return:
      • Increased blood volume: A sudden, significant increase in blood volume can lead to a rise in cardiac output (up to 2.5-3 times normal).
      • Acute venous dilation: Sudden inactivity of the sympathetic nervous system can cause peripheral blood vessels, especially veins, to dilate. This leads to a pooling of blood in the vessels and decreased venous return.
      • Decreased blood volume: A decrease in blood volume can also reduce venous return. This can occur due to fluid loss, such as from bleeding or dehydration.
    • Peripheral factors: A decrease in total peripheral resistance can increase venous return and cardiac output.
      • Vasodilator products released by tissues: As oxygen usage increases in tissues, vasodilator substances are released, which lower total peripheral resistance.
      • Anemia: Anemia can cause vasodilation and lower total peripheral resistance.

    Cardiac Shock

    • Cardiac shock is a serious condition that occurs when the cardiac output is insufficient to meet the body's needs.
    • It often results from a damaged heart that cannot pump enough blood.
    • Cardiac shock can be lethal within a few minutes to hours.

    Blood Flow Regulation

    • Blood flow regulation in most tissues is mainly proportional to their metabolism.
    • Exercise leads to increased tissue oxygen consumption, which is directly linked to increased blood flow.
    • Cardiac output, the amount of blood pumped by the heart per minute, generally increases in direct proportion to oxygen consumption and work output during exercise.

    Cardiac Output Variation

    • Cardiac output is influenced by systemic factors that control local blood flow.
    • Venous return, the blood flowing back to the heart, is directly related to the sum of all local blood flows.
    • The heart automatically pumps the returning venous blood back into the arteries, maintaining blood circulation.

    Inverse Relationship Between Cardiac Output and Peripheral Resistance

    • Cardiac output varies inversely with total peripheral vascular resistance, assuming constant arterial pressure.
    • Increased peripheral resistance, meaning narrower blood vessels, leads to reduced cardiac output.
    • Decreased peripheral resistance, meaning wider blood vessels, leads to increased cardiac output.

    Factors Affecting Cardiac Output

    • Obstructed Large Veins: This rare condition impedes blood flow back to the heart, significantly decreasing cardiac output.
    • Myocardial Infarction (Heart Attack): Severe coronary blood vessel blockage can drastically reduce cardiac output.
    • Valvular Heart Disease: Significant heart valve dysfunction can impair blood flow, resulting in decreased cardiac output.
    • Myocarditis (Heart Inflammation): Heart inflammation can weaken the heart muscle, lowering cardiac output.
    • Circulatory Shock: This life-threatening condition occurs if cardiac output falls below the level needed for adequate tissue nutrition.

    Quantitative Analysis of Cardiac Output Regulation

    • Mean circulatory filling pressure (MCFP): The equilibrium pressure in the circulatory system when blood flow is stopped. It reflects the "tightness" of blood filling the circulatory system.
    • Increased blood volume raises MCFP: More blood stretching the blood vessels increases the pressure within the circulatory system.
    • Sympathetic Stimulation Effects on MCFP: Strong sympathetic stimulation increases MCFP by constricting blood vessels and enhancing heart pumping.
    • Sympathetic Inhibition Effects on MCFP: Complete inhibition of the sympathetic nervous system relaxes blood vessels and heart, reducing MCFP.

    Mean Systemic Filling Pressure (MSFP)

    • MSFP is related to the volume of blood in the veins and the ability of the veins to distend.
    • Increased MSFP shifts the venous return curve upward and to the right, indicating increased capacity for blood return to the heart.
    • Decreased MSFP shifts the venous return curve downward and to the left, indicating reduced capacity for blood return to the heart.

    The Venous Return Curve

    • The venous return curve describes the relationship between right atrial pressure (RAP) and venous return.
    • Factors affecting the venous return curve include respiratory activity, posture, and blood volume changes.

    Cardiac Output Curves

    • Cardiac output curves are used to understand cardiac output regulation in stressful situations.
    • Different factors can shift the cardiac output curve, reflecting changes in the relationship between heart pumping capacity and blood return.
    • Examples include respiratory activity, cardiac tamponade, and changes in sympathetic nervous system activity.

    Cardiac Output and Venous Return

    • Cardiac output is the volume of blood pumped by the heart per minute.
    • Total peripheral resistance is the resistance to blood flow in the systemic circulation.
    • There is a reciprocal relationship between cardiac output and total peripheral resistance.
    • Increased total peripheral resistance leads to a decrease in cardiac output.
    • Decreased total peripheral resistance leads to an increase in cardiac output.
    • Cardiac output can be influenced by factors such as:
      • Heart rate
      • Contractility
      • Venous return
    • Venous return is the volume of blood returning to the heart from the veins.

    Mean Circulatory Filling Pressure

    • Mean circulatory filling pressure (MCFP) is the average pressure in the circulatory system when blood flow is stopped.
    • MCFP is influenced by blood volume and the capacitance of the circulatory system.
    • Increased blood volume results in increased MCFP.
    • Increased capacitance results in decreased MCFP.
    • Sympathetic activity can influence both blood volume and capacitance, thereby influencing MCFP.
    • Maximum sympathetic stimulation increases MCFP to approximately twice its normal value.
    • Complete inhibition of the sympathetic nervous system decreases MCFP to approximately 4 mm Hg.

    Venous Return Curve

    • Venous return curve describes the relationship between right atrial pressure and venous return.
    • Increased right atrial pressure decreases venous return by reducing the pressure gradient driving venous return.
    • Increased venous resistance decreases venous return.
    • Increased arteriolar resistance decreases venous return.

    Factors Affecting MCFP and Venous Return

    • Blood volume impacts the MCFP.
    • Capacitance of the circulatory system, mainly influenced by the veins, impacts the MCFP.
    • Venous pressure and, to a lesser extent, arteriolar and small artery resistances affect venous return.

    Nervous Excitation and Cardiac Pumping

    • Sympathetic stimulation and parasympathetic inhibition increase heart rate and contractility.
    • Acute venous dilation occurs most often due to sudden inactivation of the sympathetic nervous system, leading to pooling of blood in the veins.
    • Fainting can result from sudden loss of sympathetic nervous system activity.

    Cardiac Output Regulation

    • Cardiac output is primarily controlled by peripheral factors that determine venous return in normal conditions.
    • Venous return is the amount of blood returning to right atrium each minute.
    • Cardiac Output and Venous Return are generally equal
    • Blood volume can increase venous return up to 2.5 times normal level.
    • Cardiac Output is limited by the heart's pumping ability.
    • Hypertrophic heart in athletes can increase cardiac output up to 30-40L/min.

    Factors Influencing Cardiac Output

    • Hypoeffective heart occurs when the heart's pumping ability is decreased.
    • Causes of Hypoeffective Heart include diminished red blood cell concentration, loss of blood volume, acute venous dilation.
    • Peripheral factors are typically the cause of decreased Cardiac Output.
    • Circulatory Shock is a life threatening condition.
    • Circulatory Shock is caused by a cardiac output insufficient to meet the body's needs.

    Quantitive Analysis of Cardiac Output Regulation

    • Venous return curve is a quantitative representation of the relationship between venous return and right atrial pressure.
    • Cardiac output curve is a quantitative representation of the relationship between cardiac output and right atrial pressure.
    • Right atrial pressure is a critical factor in both of these curves.

    Factors Shifting Venous Return Curves

    • Increased intrathoracic pressure shifts the curve to the left.
    • Intrathoracic pressure is the pressure inside the chest cavity.
    • Negative pressure breathing shifts the curve to the left, decreasing venous return.
    • Positive pressure breathing shifts the curve to the right, increasing venous return.
    • Cardiac tamponade shifts the curve to the right, decreasing venous return.
    • Cardiac tamponade is a condition in which fluid accumulates in the pericardial sac, compressing the heart,

    Factors Influencing Right Atrial Pressure

    • Right Atrial Pressure is closely related to venous return.
    • Right Atrial Pressure is also related to cardiac output.
    • Zero venous return occurs when the Right Atrial pressure reaches about +7 mmHg.
    • A slight increase in right atrial pressure causes a significant decrease in venous return, leading to decreased cardiac output.

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    Cardiac Output, Venous Return, and Their Regulation PDF

    Description

    Explore the complex interactions between external pressures and cardiac output. This quiz covers topics including intrapleural pressure, circulatory shock, and factors affecting venous return vital for understanding heart function. Test your knowledge on cardiac output curves and their regulation.

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