Cardiac Cycle Overview
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Questions and Answers

Which of the following factors does NOT affect stroke volume?

  • Preload
  • Afterload
  • Contractility
  • Respiratory Rate (correct)

    • Frank Starling's Law states that the strength of the heart's contraction is determined by the amount of blood filling the heart.

    True

    What is the significance of preload in cardiovascular physiology?

    Preload influences the volume of blood the ventricles receive, affecting stroke volume and cardiac output.

    The hormone ______________ is released from the adrenal medulla and enhances heart rate and contractility.

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

    Match the following terms with their correct descriptions:

    <p>Preload = The amount of blood in the ventricles at the end of diastole Afterload = The resistance the heart must overcome to eject blood Contractility = The strength of the heart's contraction Atrial (Bainbridge) reflex = Increased heart rate from venous return stimulation</p> Signup and view all the answers

    Which phase of the cardiac cycle involves the heart muscles contracting to eject blood into the arteries?

    <p>Ventricular ejection</p> Signup and view all the answers

    Diastole refers to the phase of the cardiac cycle when the heart is contracting.

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

    What is the relationship between atrial systole and ventricular filling?

    <p>Atrial systole facilitates ventricular filling as it pushes blood into the ventricles.</p> Signup and view all the answers

    The units of measurement for cardiac output (CO) are _____ per minute.

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

    Which statement correctly relates stroke volume (SV) to its components?

    <p>SV is the difference between end systolic volume and end diastolic volume.</p> Signup and view all the answers

    The Frank-Starling Law states that the heart pumps more blood when it is filled with more blood during diastole.

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

    Define preload in the context of cardiac mechanics.

    <p>Preload is the degree of stretch of the cardiac muscle fibers at the end of diastole.</p> Signup and view all the answers

    Match the following cardiac terms with their definitions:

    <p>Cardiac output = The volume of blood pumped by the heart per minute Stroke volume = The volume of blood pumped out of the ventricle with each heartbeat End diastolic volume = The maximum volume of blood in the ventricle just before contraction End systolic volume = The volume of blood left in the ventricle after contraction</p> Signup and view all the answers

    What phase of the cardiac cycle represents the heart's contraction?

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

    Atrial depolarization is represented by the QRS complex.

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

    What is the significance of the AV node during the cardiac cycle?

    <p>It delays the impulse to ensure atrial systole before ventricular contraction.</p> Signup and view all the answers

    The __________ phase comes after ventricular depolarization in the cardiac cycle.

    <p>ventricular systole</p> Signup and view all the answers

    Match the cardiac events with their corresponding components:

    <p>Atrial depolarization = P wave Ventricular depolarization = QRS complex Ventricular repolarization = T wave Atrial repolarization = Part of QRS complex</p> Signup and view all the answers

    Which sound is associated with the completion of ventricular repolarization?

    <p>2nd sound</p> Signup and view all the answers

    Mechanical events of the heart occur simultaneously with electrical events.

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

    What occurs during the isovolumetric relaxation phase?

    <p>All heart valves are closed and the volume of blood in the ventricles remains constant as they relax.</p> Signup and view all the answers

    During __________, the heart is known to be at rest and filling with blood.

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

    Which of the following best defines the cardiac cycle?

    <p>All events associated with blood flow through the heart in one heartbeat</p> Signup and view all the answers

    What does the stroke volume (SV) represent?

    <p>The volume of blood pumped out by the ventricle with each beat</p> Signup and view all the answers

    Increased preload will decrease stroke volume.

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

    What formula is used to calculate cardiac output (CO)?

    <p>CO = HR x SV</p> Signup and view all the answers

    The volume of blood in each ventricle at the end of diastole is known as ________.

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

    Match each term with its correct definition:

    <p>Preload = Degree of stretch of cardiac muscle cells before contraction Contractility = The inherent strength and vigor of heart contractions Afterload = The pressure the heart must work against to eject blood ESV = Volume of blood remaining in each ventricle after contraction</p> Signup and view all the answers

    Which factor does NOT directly affect stroke volume?

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

    Cardiac output is the total volume of blood pumped out in one minute.

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

    What is the average stroke volume in milliliters?

    <p>70 ml</p> Signup and view all the answers

    According to the Frank-Starling law, increased blood return to the heart stretches the ventricles and increases ________.

    <p>contraction force</p> Signup and view all the answers

    What is the volume of blood remaining in each ventricle after contraction known as?

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

    What is the primary factor that influences stroke volume according to Starling's law?

    <p>Venous return</p> Signup and view all the answers

    Increased stroke volume is achieved by decreasing venous return.

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

    What effect does exercise have on venous return?

    <p>Exercise increases venous return.</p> Signup and view all the answers

    The distension of ventricular walls increases _____ and consequently the stroke volume.

    <p>contraction force</p> Signup and view all the answers

    Match the following mechanisms with their role in aiding venous return:

    <p>Muscular pump = Helps blood flow towards the heart by skeletal muscle contraction Respiratory pump = Moves blood toward heart during breathing Valves = Prevent backflow of blood Abdominal pressure = Facilitates blood flow toward chest during inhalation</p> Signup and view all the answers

    Which of the following is NOT a method aiding venous return?

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

    A slow heartbeat decreases venous return.

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

    What are the two main factors that increase venous return?

    <p>Slow heartbeat and exercise.</p> Signup and view all the answers

    The Frank-Starling law explains the relationship between venous return, ____ and stroke volume.

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

    What happens to stroke volume when venous return is increased?

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

    What effect does increased afterload have on stroke volume?

    <p>Decreases stroke volume by increasing ESV.</p> Signup and view all the answers

    Which of the following would be classified as a positive ionotropic factor?

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

    What occurs in the heart due to sustained increases in calcium levels in congestive heart failure?

    <p>The architecture of cardiac myocytes is altered.</p> Signup and view all the answers

    Which chemical would likely decrease contractility in cardiac muscle?

    <p>Increased extracellular K+</p> Signup and view all the answers

    How do sympathetic stimulation and calcium influence stroke volume?

    <p>Sympathetic stimulation increases calcium, enhancing contractility and stroke volume.</p> Signup and view all the answers

    During which phase does the majority of blood enter the ventricles passively?

    <p>Ventricular filling</p> Signup and view all the answers

    What initiates atrial systole in the cardiac cycle?

    <p>Wave of depolarization (P wave)</p> Signup and view all the answers

    What happens during the isovolumetric contraction phase of the cardiac cycle?

    <p>All valves are closed while pressure builds</p> Signup and view all the answers

    What describes the end diastolic volume (EDV) in the cardiac cycle?

    <p>Volume of blood in each ventricle at the end of diastole</p> Signup and view all the answers

    Which heart sound is associated with the closure of the AV valves during the cardiac cycle?

    <p>First heart sound</p> Signup and view all the answers

    What occurs when the pressure in the ventricles exceeds the pressure in the large arteries?

    <p>Opening of the SL valves</p> Signup and view all the answers

    Which component is represented by the end systolic volume (ESV) in the cardiac cycle?

    <p>Volume of blood left in the ventricles after contraction</p> Signup and view all the answers

    Which electrical event marks the completion of the ventricular filling phase?

    <p>QRS wave</p> Signup and view all the answers

    During which phase of the cardiac cycle does isovolumetric relaxation occur?

    <p>Early diastole</p> Signup and view all the answers

    What occurs following the closure of the SL valves during isovolumetric relaxation?

    <p>A rapid drop in ventricular pressure</p> Signup and view all the answers

    What is the term for the brief rise in aortic pressure caused by blood rebounding off the closed SL valves?

    <p>Dicrotic notch</p> Signup and view all the answers

    What sound is associated with the closure of the SL valves during the cardiac cycle?

    <p>The second heart sound</p> Signup and view all the answers

    What is the mathematical relationship represented by the formula $CO = HR \times SV$?

    <p>The total volume of blood pumped per minute</p> Signup and view all the answers

    In isovolumetric relaxation, what is happening to the pressure in the ventricles compared to the aorta and pulmonary arteries?

    <p>Pressure in the ventricles is lower than in the aorta</p> Signup and view all the answers

    Which factor primarily determines the stroke volume (SV) according to the relationship $SV = EDV - ESV$?

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

    Which of the following is NOT a characteristic of isovolumetric relaxation?

    <p>AV valves are open</p> Signup and view all the answers

    How does the Frank-Starling law explain cardiac output in relation to venous return?

    <p>Increased venous return stretches ventricles, enhancing contraction strength</p> Signup and view all the answers

    What causes the pulmonary arteries and aorta to experience a rapid increase in pressure during this phase?

    <p>Rebound of blood against closed SL valves</p> Signup and view all the answers

    Which of the following correctly describes preload?

    <p>The degree to which cardiac muscle cells are stretched before contraction</p> Signup and view all the answers

    Which statement about the events in early diastole is correct?

    <p>The SL valves are closed due to high pressure in pulmonary arteries and aorta</p> Signup and view all the answers

    During which electrical event on an ECG does isovolumetric relaxation begin?

    <p>T wave</p> Signup and view all the answers

    During which phase of the cardiac cycle does ventricular filling occur?

    <p>Ventricular diastole</p> Signup and view all the answers

    What is the average stroke volume (SV) during a typical cardiac cycle?

    <p>70 ml per beat</p> Signup and view all the answers

    What describes the pressure in the ventricles during the isovolumetric relaxation phase?

    <p>Rapidly decreasing</p> Signup and view all the answers

    Which factor has the greatest influence on the preload of cardiac muscles?

    <p>Venous return</p> Signup and view all the answers

    What main physiological characteristic affects the contractility of the heart?

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

    What happens to stroke volume when preload is increased?

    <p>Stroke volume increases</p> Signup and view all the answers

    How do skeletal muscle contractions affect venous return?

    <p>They help propel blood toward the heart.</p> Signup and view all the answers

    Which of the following best defines the role of contractility in the cardiac cycle?

    <p>The amplitude of the heart's contraction strength</p> Signup and view all the answers

    In what way does a slow heartbeat affect stroke volume?

    <p>It increases venous return.</p> Signup and view all the answers

    What physiological mechanism helps blood return to the heart during inhalation?

    <p>Increased pressure in abdominal veins</p> Signup and view all the answers

    How does a slow heartbeat influence cardiac output?

    <p>Increases venous return and stroke volume</p> Signup and view all the answers

    According to Starling's law, which of the following statements is true?

    <p>Increased stretch of cardiac muscle enhances stroke volume.</p> Signup and view all the answers

    Which of the following is NOT a factor aiding in venous return?

    <p>High blood pressure</p> Signup and view all the answers

    What effect does an increase in end-diastolic volume (EDV) have on stroke volume (SV)?

    <p>SV increases proportionally.</p> Signup and view all the answers

    Which of the following statements best describes the relationship between venous return and stroke volume?

    <p>Increased venous return typically raises stroke volume.</p> Signup and view all the answers

    What role do heart valves play in venous return?

    <p>They maintain unidirectional blood flow.</p> Signup and view all the answers

    Which of the following actions would likely reduce venous return?

    <p>Straining during bowel movements</p> Signup and view all the answers

    What is the primary event that occurs during the T wave in the cardiac cycle?

    <p>Ventricular repolarization</p> Signup and view all the answers

    Which phase of the cardiac cycle directly follows ventricular systole?

    <p>Isovolumetric relaxation</p> Signup and view all the answers

    What part of the heart's electrical conduction system ensures a delay before ventricular contraction?

    <p>AV node</p> Signup and view all the answers

    During which part of the cardiac cycle does the first heart sound (S1) occur?

    <p>Isovolumetric contraction</p> Signup and view all the answers

    Which event is characterized by a series of pressure changes and the efficient pumping of blood by the heart?

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

    What marks the transition from atrial systole to ventricular systole?

    <p>Closure of the AV valves</p> Signup and view all the answers

    Which of the following describes the relationship between electrical and mechanical events in the heart?

    <p>Mechanical events always follow electrical events</p> Signup and view all the answers

    During the cardiac cycle, when does the majority of blood enter the ventricles?

    <p>During passive ventricular filling</p> Signup and view all the answers

    Which factor is primarily responsible for increasing stroke volume through enhanced contractility?

    <p>Increased calcium concentration</p> Signup and view all the answers

    What is the primary effect of hypertension on afterload and stroke volume?

    <p>Increases afterload resulting in higher ESV and reduced stroke volume</p> Signup and view all the answers

    Which of the following substances is classified as a negative ionotropic factor?

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

    What physiological change occurs in cardiac myocytes due to chronic congestive heart failure?

    <p>Altered architecture in response to sustained calcium increase</p> Signup and view all the answers

    Which statement correctly describes the role of adenylate cyclase in cardiac muscle contraction?

    <p>Converts ATP to cAMP, enhancing calcium entry into the cytoplasm</p> Signup and view all the answers

    What primarily causes the rapid drop in pressure in the ventricles during isovolumetric relaxation?

    <p>Majority of blood has passed into the arteries</p> Signup and view all the answers

    Which event corresponds to the closure of the semilunar valves in the cardiac cycle?

    <p>Backflow of blood from the aorta</p> Signup and view all the answers

    What is the physiological significance of the dicrotic notch observed in the pressure tracing of the aorta?

    <p>Reflects the rebound of blood off the closed semilunar valves</p> Signup and view all the answers

    During early diastole, what happens immediately after the T wave in the electrocardiogram?

    <p>Isovolumetric relaxation starts</p> Signup and view all the answers

    Which phase of the cardiac cycle directly follows the ventricular ejection phase?

    <p>Isovolumetric relaxation phase</p> Signup and view all the answers

    What characterizes the atrioventricular and semilunar valves during isovolumetric relaxation?

    <p>Both valves are closed</p> Signup and view all the answers

    What leads to the second heart sound during the cardiac cycle?

    <p>Closure of the semilunar valves</p> Signup and view all the answers

    Which occurrence marks the transition from ventricular systole to diastole?

    <p>Closure of the semilunar valves</p> Signup and view all the answers

    What is the primary consequence of the rapid increase of pressure in the pulmonary arteries during isovolumetric relaxation?

    <p>Dicrotic notch formation</p> Signup and view all the answers

    What is the primary regulator of stroke volume according to the relationship described?

    <p>The amount of blood returned to the ventricle</p> Signup and view all the answers

    Which of the following formulas correctly represents the calculation for stroke volume?

    <p>SV = EDV - ESV</p> Signup and view all the answers

    During what condition does increased preload result in an augmented stroke volume?

    <p>During vigorous exercise sessions</p> Signup and view all the answers

    How is cardiac output calculated from stroke volume and heart rate?

    <p>CO = SV x HR</p> Signup and view all the answers

    Which statement about end-diastolic volume (EDV) is accurate?

    <p>EDV represents the blood volume before the ventricles contract.</p> Signup and view all the answers

    Which component is NOT directly affecting stroke volume?

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

    What effect does increased afterload have on stroke volume?

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

    Which factor contributes to the increase in stroke volume under normal physiological conditions?

    <p>Enhanced contractility</p> Signup and view all the answers

    According to Frank-Starling's law, increased blood return to the heart leads to what result?

    <p>Increased stroke volume due to enhanced ventricular stretch.</p> Signup and view all the answers

    Which of the following best defines cardiac output (CO)?

    <p>The amount of blood pumped out by each ventricle in one minute</p> Signup and view all the answers

    What is the primary mechanism by which the muscular pump aids venous return?

    <p>Contraction of skeletal muscles</p> Signup and view all the answers

    Which condition would most likely lead to a decrease in stroke volume?

    <p>Increased afterload</p> Signup and view all the answers

    Which of the following factors is least likely to influence venous return?

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

    What role does the respiratory pump play in venous return?

    <p>Increases thoracic cavity volume during inhalation</p> Signup and view all the answers

    How would a reduced heart rate influence stroke volume?

    <p>Increase stroke volume by prolonging diastolic filling</p> Signup and view all the answers

    According to Starling’s law, what happens when the cardiac muscle is stretched further?

    <p>Stroke volume increases</p> Signup and view all the answers

    What is the effect of exercise on venous return?

    <p>Increased muscle pump activity</p> Signup and view all the answers

    What is the overall relationship described by the Frank-Starling law?

    <p>Increased venous return leads to increased stroke volume</p> Signup and view all the answers

    Which factor most directly affects preload in the heart?

    <p>Venous return</p> Signup and view all the answers

    What physiological change occurs during inhalation that aids in venous return?

    <p>Decreased thoracic cavity pressure</p> Signup and view all the answers

    Cardiac output is defined as the total volume of blood pumped out in one minute and is measured in liters.

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

    End diastolic volume (EDV) is the volume of blood remaining in each ventricle after contraction.

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

    The phases of the cardiac cycle include atrial filling, isovolumetric contraction, atrial ejection, and isovolumetric relaxation.

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

    During isovolumetric relaxation, all heart valves are closed and the heart is at rest.

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

    The Frank-Starling Law states that increased venous return directly decreases stroke volume.

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

    Ventricular depolarization is represented by the P wave.

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

    During isovolumetric relaxation, all heart valves are open allowing blood to flow freely.

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

    The first heart sound occurs during the completion of ventricular repolarization.

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

    Atrial systole delivers 80% of the blood volume to the ventricles.

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

    The end diastolic volume (EDV) represents the volume of blood remaining in each ventricle after contraction.

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

    Atrial systole involves the contraction of the atria to fill the ventricles with blood.

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

    Systole refers to the relaxation phase of the cardiac cycle.

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

    The isovolumetric contraction phase occurs when all heart valves are open.

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

    The first heart sound is associated with the closure of the semilunar valves.

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

    Electrically, atrial depolarization is represented by the QRS wave on the ECG.

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

    Study Notes

    Cardiac Cycle

    • The cardiac cycle encompasses all events associated with blood flow during one heartbeat.
    • Systole is the contraction phase, pushing blood out.
    • Diastole is the relaxation phase, allowing chambers to refill.

    Phases of the Cardiac Cycle

    • Ventricular Filling:
      • Passive filling occurs first as pressure in atria exceeds that in ventricles, filling the ventricles by 70%.
      • Atrial systole, atrial contraction, contributes the remaining 30%, actively filling the ventricles.
      • This phase corresponds to the P wave on an ECG.
    • Isovolumetric Contraction:
      • Ventricles start contracting, but all valves remain closed, increasing pressure inside.
      • This phase marks the beginning of ventricular systole.
      • It corresponds to the QRS complex on an ECG.
    • Ventricular Ejection:
      • Pressure inside ventricles exceeds that in aorta and pulmonary trunk, opening the semilunar valves.
      • Blood is ejected into the aorta and pulmonary trunk.
      • This phase corresponds to the plateau of the T wave on an ECG.
    • Isovolumetric Relaxation:
      • Ventricles start to relax, pressure drops.
      • All valves remain closed until ventricular pressure drops below that in atria.
      • Corresponding with the end of the T wave, the heart is preparing for the next cycle.

    Cardiac Output (CO)

    • The volume of blood pumped by each ventricle in one minute.
    • CO = Heart rate (HR) x Stroke volume (SV)
      • HR: number of beats per minute.
      • SV: volume of blood pumped out by one ventricle with each beat.

    Stroke Volume (SV)

    • The volume of blood ejected from the ventricle with each beat: SV = EDV – ESV.
      • EDV: End Diastolic Volume, the volume of blood in the ventricle at the end of diastole (ventricular relaxation).
      • ESV: End Systolic Volume, the volume of blood remaining in the ventricle after systole (ventricular contraction).
    • Factors affecting SV:
      • Preload: The degree of stretch of cardiac muscle cells before contraction.
        • Increased preload generally leads to increased SV.
        • Venous return is the most important factor influencing preload.
      • Contractility: The inherent strength of the heart muscle.
        • Positive inotropic agents increase contractility and SV.
        • Negative inotropic agents decrease contractility and SV.
      • Afterload: The resistance the ventricle must overcome to eject blood.
        • Increased afterload generally leads to decreased SV.

    Frank-Starling Law of the Heart

    • Increased venous return stretches the ventricle, increasing contraction force.
    • This leads to an increased SV, enhancing circulatory efficiency.
    • This mechanism is crucial for adapting to increased demands, such as exercise.

    Regulation of Stroke Volume

    • Venous return (the volume of blood returning to the heart) is the primary factor influencing preload and SV.
    • Factors aiding venous return:
      • Muscular pump: Contraction of skeletal muscles "milks" blood toward the heart.
      • Respiratory pump: Pressure changes during breathing aid blood flow towards the heart.

    Autonomic Nervous System Regulation

    • The autonomic nervous system regulates HR and hence CO.
    • Sympathetic stimulation increases HR and contractility; parasympathetic stimulation decreases HR.
    • Atrial (Bainbridge) Reflex: Increased venous return stretches atrial walls, stimulating the SA node to increase HR.

    Chemical Regulation of Heart Rate

    • Hormones
      • Epinephrine (from adrenal medulla) increases HR and contractility.
      • Thyroxine (from thyroid gland) enhances HR and the effects of epinephrine.
    • Ion concentrations: Maintaining proper intracellular and extracellular ion concentrations (like Ca2+ and K+) is essential for normal heart function.

    Ventricular Filling

    • Occurs in mid-to-late diastole
    • AV valves open, SL valves closed
    • 80% of blood passively flows into ventricles
    • Transition into atrial systole begins after depolarization
    • Atrial systole delivers the remaining 20% blood volume
    • Ventricles are at end diastole, having received nearly 100% of their blood volume
    • End diastolic volume(EDV): volume of blood in each ventricle at the end of diastole

    Ventricular Systole

    • Atria are relaxed (diastole)
    • Ventricles begin to contract (wave of depolarization just occurred), raising ventricular pressure and closing the AV valves (first heart sound)
    • Isovolumetric contraction phase occurs, all valves closed
    • Ventricles contract (full systole, end of QRS wave)
    • With ventricular contraction, pressure exceeds pressure in the large arteries, forcing the SL valves open
    • Blood flows into the pulmonary arteries and aorta (ejection phase)
    • End systolic volume (ESV): volume of blood remaining in each ventricle after contraction.
    • Ventricular relaxation begins after ESV

    Isovolumetric Relaxation

    • Occurs in early diastole (following T wave on ECG)
    • Ventricles relax
    • Rapid drop in ventricular pressure, high pressure in the pulmonary arteries and aorta
    • Backflow of blood in the aorta and pulmonary trunk closes the SL valves
    • Closure of the SL valves leads to a rapid increase in pulmonary artery and aortic pressure, causing the dicrotic notch (brief rise in aortic pressure)
    • This is the second heart sound

    Phases of the Cardiac Cycle

    • Ventricular filling
      • Mid-to-late diastole
      • Atrial systole
    • Ventricular Systole
      • Isovolumetric contraction
      • Ejection phase
    • Early diastole
      • Isovolumetric relaxation

    Useful Terms

    • EDV (end diastolic volume)
    • ESV (end systolic volume)
    • SV (stroke volume)
    • CO (cardiac output)
    • CO = HR * SV
    • SV = EDV - ESV

    Cardiac Output

    • Volume of blood pumped by each ventricle in one minute
    • CO = HR * SV
    • HR = number of beats per minute
    • SV = volume of blood pumped by a ventricle with each beat

    Regulation of Stroke Volume

    • SV = EDV - ESV
    • Avg SV = 70 ml/beat (60% of blood in chambers)
    • Preload, Contractibility, and Afterload affect SV
    • Preload: degree of stretch of cardiac muscle cells before contraction
      • Length-tension relationship
      • INCREASED PRELOAD  INCREASED SV
      • Slow heartbeat and exercise increase venous return, increase EDV, SV and force of contraction
      • Frank-Starling law of heart: increased blood return stretches ventricles and increases contraction force so more is propelled out.
      • VENOUS RETURN is the most important factor
      • Anything increasing venous return (volume or speed) increases EDV, SV, contraction and force.
    • Contractility: contractile strength
      • Independent of muscle stretch and EDV
      • Increased SV, decreased ESV
      • Increased Ca2+ from sympathetic stimulation
      • Positive Ionotropic Factors
        • Epinephrine
        • Thyroxine
        • Glucagon
        • Digitalis
        • High extracellular Ca++
      • Negative Ionotropic Factors
        • Acidosis
        • Increased extracellular K+
        • Calcium channel blockers
    • Afterload: pressure ventricles must overcome to eject blood
      • Backpressure from blood in aorta and pulmonary vessels
      • Hypertension increases afterload, resulting in increased ESV and reduced SV

    Factors Aiding Venous Return

    • Muscular pump
    • Respiratory pump
    • Venoconstriction

    Congestive Heart Failure (CHF)

    • CO is so low that blood circulation cannot meet tissue needs
    • Heart attempts to work harder, increasing Ca2+ levels in cardiac cells
    • Sustained increase in Ca2+ leads to altered heart architecture
    • Caused by:
      • Coronary atherosclerosis
      • Persistent high blood pressure
      • Dead cardiac cells from heart attacks
      • Dilated cardiomyopathy (DCM)

    Cardiac Anatomy & Heart Sounds

    • The SA node depolarizes, represented by the P wave on the ECG.
    • The impulse is delayed at the AV node, allowing for atrial systole (contraction).
    • Ventricular depolarization creates the QRS complex on the ECG, while atrial repolarization also occurs. Ventricular systole begins.
    • Ventricular depolarization is complete, and ventricular systole continues. The first heart sound occurs as the AV valves close.
    • Ventricular repolarization is represented by the T wave on the ECG.
    • Ventricular repolarization is complete. The second heart sound occurs as the semilunar valves close.

    Mechanical Events: The Cardiac Cycle

    • The heart functions as an efficient pump, driven by pressure and volume changes.
    • Mechanical events follow electrical events.
    • The cardiac cycle encompasses all events associated with blood flow through the heart during one heartbeat.
    • Systole refers to contraction, while diastole refers to relaxation.

    Phases of the Cardiac Cycle

    • Isovolumetric relaxation occurs at the beginning of diastole (after the T wave).
      • Ventricles relax, pressure decreases, and the majority of blood has been ejected into the pulmonary artery and aorta.
      • The decrease in ventricular pressure, combined with higher pressure in the pulmonary artery and aorta, causes a backflow of blood. This closes the semilunar valves, contributing to the second heart sound.
    • Ventricular filling occurs during diastole.
      • The AV valves are open.
      • Blood passively flows from atria to ventricles.
      • Atrial contraction occurs, contributing to ventricular filling.
    • Isovolumetric contraction occurs at the beginning of systole.
      • The AV valves close before the semilunar valves open.
      • Ventricular pressure increases, but no blood is ejected yet.
    • Ventricular ejection occurs during systole.
      • Semilunar valves open and blood is ejected into the aorta and pulmonary artery.
      • The pressure in the ventricles is higher than the pressure in the aorta and pulmonary artery.

    Useful Terms

    • EDV (End Diastolic Volume): The volume of blood in each ventricle at the end of diastole (relaxation).
    • ESV (End Systolic Volume): The volume of blood remaining in each ventricle after contraction.
    • SV (Stroke Volume): The volume of blood pumped out by the ventricle with each beat (EDV - ESV).
    • CO (Cardiac Output): The amount of blood pumped out by each ventricle in 1 minute (HR x SV).

    Regulation of Stroke Volume

    • SV = EDV - ESV, meaning the volume pumped out is the total volume filled minus the remaining volume after contraction.
    • Three main factors influence SV: preload, contractility, and afterload.

    Preload

    • Preload: degree of stretch of cardiac muscle cells before contraction.
    • Increased preload leads to increased SV.
    • Slow heartbeat and exercise increase venous return, leading to increased EDV and SV.
    • Frank-Starling law of the heart: Increased venous return stretches ventricles and increases contraction force, resulting in more blood being propelled out.

    Factors Aiding Venous Return

    • Muscular pump: Contraction of skeletal muscles "milks" blood toward the heart. Valves prevent backflow.
    • Respiratory pump: Pressure changes during breathing move blood toward the heart. This occurs by squeezing abdominal veins as thoracic veins expand.
    • Venoconstriction: Under sympathetic control, venoconstriction pushes blood toward the heart.

    Contractility

    • Contractility: Contractile strength independent of muscle stretch and EDV.
    • Increased contractility results in increased SV and decreased ESV.
    • Increased Ca2+ from sympathetic stimulation (extrinsic factor), such as epinephrine and norepinephrine, enhance contractility.

    Chemicals Influencing Contractility

    • Positive Inotropic Agents: Increase contractility.
      • Epinephrine
      • Thyroxine
      • Glucagon
      • Digitalis (medication)
      • High extracellular Ca++
    • Negative Inotropic Agents: Decrease contractility.
      • Acidosis
      • Increased extracellular K+
      • Calcium channel blockers

    Afterload

    • Afterload: The pressure that must be overcome for the ventricles to eject blood.
    • This includes backpressure from blood in the aorta and pulmonary vessels on the valves.
    • Hypertension increases afterload, leading to increased ESV and reduced SV.

    Congestive Heart Failure (CHF)

    • Cardiac output is so low that blood circulation is inadequate to meet tissue needs.
    • The heart attempts to work harder, leading to increased Ca++ levels in cardiac cells. Sustained elevation in Ca++ can lead to increased calcineurin, which alters the structure of cardiac myocytes to adapt to increased demands.
    • Causes include:
      • Coronary atherosclerosis (clogging of arteries)
      • Persistent high blood pressure
      • Damaged cardiac cells from heart attacks
      • Dilated cardiomyopathy (DCM)

    Cardiac Mechanics

    • The Cardiac cycle is a complete heartbeat, including all events associated with blood flow through the heart.
    • Systole is the contraction phase.
    • Diastole is the relaxation phase.
    • Mechanical events follow Electrical events in the heart.

    Phases of the Cardiac Cycle

    • Ventricular Filling:
      • Takes place in mid-to-late diastole.
      • AV valves are open, SL valves are closed.
      • 80% of blood passively flows into ventricles.
      • Atrial systole delivers the remaining blood volume (20%).
      • End diastolic volume (EDV) is the volume of blood in each ventricle at the end of diastole.
    • Ventricular Systole:
      • Atria are relaxed.
      • Ventricles contract, increasing pressure and closing the AV valves (creating the first heart sound).
      • Isovolumetric contraction phase: All valves are closed, pressure builds.
      • Ventricles contract, and pressure exceeds the pressure in the aorta and pulmonary artery, forcing the SL valves open (ejection phase), allowing blood flow into the Pulmonary Artery and Aorta.
      • End systolic volume (ESV) is the volume of blood remaining in each ventricle after contraction.
    • Isovolumetric Relaxation:
      • Ventricular diastole begins.
      • Ventricles relax, pressure drops.
      • SL valves close (creating the second heart sound).
      • AV valves remain closed as pressure in the ventricles is still higher than that in the atria.

    Cardiac Output

    • Cardiac Output(CO) is the volume of blood pumped by each ventricle per minute.
    • CO = Heart Rate (HR) x Stroke Volume (SV)
    • HR: The number of heart beats per minute.
    • SV: The volume of blood pumped out by one ventricle per beat.

    Stroke Volume

    • Stroke Volume (SV) = EDV - ESV
    • The volume of blood pumped out by the ventricle is the total volume it fills with, minus the amount left in the heart after contraction.
    • Three main factors affect SV:
      • Preload: the degree of stretch of cardiac muscle cells before they contract (length-tension relationship).
      • Contractility: the contractile strength of the heart muscle.
      • Afterload: the pressure that must be overcome for ventricles to eject blood.

    Preload

    • Increased Preload leads to increased Stroke Volume.
    • Slow heartbeat and exercise increase venous return, which increases EDV, SV, and force of contraction.
    • The Frank-Starling Law of the heart: Increased blood return stretches ventricles and increases contraction force, propelling more blood out.

    Contractility

    • Contractility is independent of muscle stretch and EDV (intrinsic factors).
    • Increased Ca2+ from sympathetic stimulation (extrinsic factor) increases Contractility and decreases ESV.
    • Positive Ionotropic Agents: Chemicals that increase Contractility, such as Epinephrine, Thyroxine, Glucagon, Digitalis, and high extracellular Ca++.
    • Negative Ionotropic Agents: Chemicals that decrease Contractility, such as Acidosis, increased extracellular K+, and calcium channel blockers.

    Afterload

    • Afterload is the backpressure from blood in the aorta and pulmonary vessels on the valves.
    • Hypertension increases Afterload, resulting in increased ESV and reduced SV.

    Congestive Heart Failure (CHF)

    • Occurs when CO is so low that blood circulation is inadequate to meet tissue needs.
    • Caused by: coronary atherosclerosis, persistent high blood pressure, dead cardiac cells from heart attacks, dilated cardiomyopathy.

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    Description

    This quiz explores the cardiac cycle, detailing the phases involved in one heartbeat. Understand the systole and diastole events and how they correspond to the ECG waves. Test your knowledge on the mechanisms of ventricular filling, isovolumetric contraction, and ventricular ejection.

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