Cardiac Mechanics and Function
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Questions and Answers

Which factor is NOT an important mechanism for changing the force of cardiac contraction?

  • The availability of Ca2+
  • The synchrony of activation
  • The resting muscle stretch
  • The % of activated muscle cells (correct)

    • Which factor primarily regulates the contractility of the heart?

  • The sympathetic nervous system (correct)
  • The synchrony of activation
  • The % of activated muscle cells
  • The availability of Ca2+

    • Which factor determines the overlap of actin and myosin in cardiac muscle?

  • The resting muscle stretch (correct)
  • The availability of Ca2+
  • The synchrony of activation
  • The % of activated muscle cells

    • What is the molecular makeup of the muscle that can influence the mechanical properties of the heart?

    <p>The contractile protein isoform expression</p> Signup and view all the answers

    Which factor can change the mechanical properties of the twitch contraction in the heart?

    <p>The duration of the active state</p> Signup and view all the answers

    Which factor is an important determinant of ventricular force generation?

    <p>The synchrony of activation</p> Signup and view all the answers

    What determines the size of the Ca transient in the heart?

    <p>The availability of Ca2+</p> Signup and view all the answers

    Which type of muscle is easily stretched at short muscle lengths?

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

    What is the protective mechanism in the whole heart that prevents overfilling?

    <p>All of the above</p> Signup and view all the answers

    What are isometric contractions in cardiac muscle?

    <p>Contractions where the muscle develops force but is prevented from shortening</p> Signup and view all the answers

    What determines the force generating capabilities of striated muscle?

    <p>The number of actin-myosin crossbridges</p> Signup and view all the answers

    What is the relationship between resting length and cardiac function called?

    <p>The Frank Starling relationship</p> Signup and view all the answers

    What is the sarcomere length beyond which it is very difficult to stretch resting cardiac muscle?

    <p>2.2 microns</p> Signup and view all the answers

    What is the primary factor that regulates force development in cardiac muscle?

    <p>The number of actin-myosin crossbridges</p> Signup and view all the answers

    What is the characteristic of resting cardiac muscle compared to skeletal muscle at sarcomere lengths near the peak of the length-active force relationship?

    <p>Resting cardiac muscle is significantly stiffer</p> Signup and view all the answers

    What are the factors that regulate force development in cardiac muscle?

    <p>Resting muscle length and the number of actin-myosin crossbridges</p> Signup and view all the answers

    Which phase of the cardiac cycle is represented by the bottom side of the pressure-volume loop?

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

    What does the width of the pressure-volume loop represent?

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

    Which event occurs at the time represented by the corner of the pressure-volume loop labeled 'AC'?

    <p>Aortic valve closure</p> Signup and view all the answers

    What determines the rate and magnitude of shortening in cardiac muscle?

    <p>The afterload and contractility</p> Signup and view all the answers

    What happens to the velocity and magnitude of shortening as the afterload increases?

    <p>They decrease</p> Signup and view all the answers

    Which type of muscle only functions on the 'ascending limb' of the length-tension relationship?

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

    What is the name of the loop that can be used to plot the instantaneous pressures and volumes throughout the cardiac cycle?

    <p>Pressure-volume loop</p> Signup and view all the answers

    When does the muscle shorten at a maximal rate?

    <p>When the afterload is zero</p> Signup and view all the answers

    Which one of these is true about the relationship between afterload and the velocity of shortening in cardiac muscle?

    <p>As afterload increases, the velocity of shortening decreases</p> Signup and view all the answers

    What is the diastolic pressure-volume relationship (DPVR) in cardiac muscle?

    <p>The relationship between ventricular pressure and volume during filling</p> Signup and view all the answers

    A decrease in diastolic ventricular compliance is represented by what?

    <p>Upward shift in the diastolic PVR</p> Signup and view all the answers

    What can cause a decrease in diastolic ventricular compliance in cardiac muscle?

    <p>All of the above</p> Signup and view all the answers

    What does the end-systolic pressure-volume relationship (ESPVR) represent in cardiac muscle?

    <p>The maximum pressure that the ventricle can develop at any volume</p> Signup and view all the answers

    How is the end-systolic pressure-volume relationship (ESPVR) derived in cardiac muscle?

    <p>By allowing the ventricle to contract but not eject blood at different end-diastolic volumes</p> Signup and view all the answers

    What happens to the maximum capability of the ventricle to develop pressure as the volume of the ventricle decreases in cardiac muscle?

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

    What happens to the velocity and magnitude of shortening as the afterload increases in cardiac muscle?

    <p>They decrease</p> Signup and view all the answers

    Which of the following is true about compliance in cardiac muscle?

    <p>Compliance is greatest at low volumes</p> Signup and view all the answers

    What is the relationship between ventricular ejection and the end-systolic pressure-volume relationship (ESPVR)?

    <p>Ventricular ejection ends when the ventricular volume intersects the ESPVR</p> Signup and view all the answers

    What is contractility in cardiac muscle?

    <p>The ventricle's ability to develop pressure independent of load</p> Signup and view all the answers

    Which of the following is true about the regulation of contractility in cardiac muscle?

    <p>Contractility is regulated by the sympathetic nervous system</p> Signup and view all the answers

    What are some indices used to estimate changes in contractility?

    <p>Emax and dP/dt</p> Signup and view all the answers

    What happens to stroke volume when contractility increases with no change in preload or afterload?

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

    How can contractility be modified in cardiac muscle?

    <p>By humoral and pharmacologic agents</p> Signup and view all the answers

    What happens to contractility in cardiac diseases?

    <p>Contractility decreases</p> Signup and view all the answers

    What causes reduced myofilament Ca binding affinity in cardiac muscle?

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

    What is associated with reduced levels of SERCa2 and 'depressed' Ca handling in cardiac muscle?

    <p>Pathological cardiac hypertrophy</p> Signup and view all the answers

    Which of the following is true about failing hearts?

    <p>They have increased sympathetic reflexes</p> Signup and view all the answers

    What is preload in the context of the heart?

    <p>The stretch on the myocardial wall at the end of diastole</p> Signup and view all the answers

    How is preload best represented?

    <p>End-diastolic volume (EDV)</p> Signup and view all the answers

    What happens when there is an increase in preload (EDV)?

    <p>The ventricle moves higher on the Starling curve</p> Signup and view all the answers

    What physiological factors can alter preload?

    <p>All of the above</p> Signup and view all the answers

    What is the problem with using end-diastolic pressure (EDP) as a measure of preload when diastolic compliance is changing?

    <p>EDP is not a reliable indicator of preload, IF THE DIASTOLIC COMPLIANCE IS CHANGING</p> Signup and view all the answers

    What can happen when + inotropic drugs are used to correct abnormal contractility in human heart failure?

    <p>They can worsen arrhythmias</p> Signup and view all the answers

    What is the effect of an increase in end-diastolic volume (EDV) on the PV loop?

    <p>It displaces the right side of the PV loop to the right</p> Signup and view all the answers

    What is the term for the reduced contractility in failing hearts?

    <p>Contractility reserve</p> Signup and view all the answers

    Why is correcting abnormal contractility in human heart failure not easily accomplished?

    <p>It can worsen arrhythmias</p> Signup and view all the answers

    Which of the following is a measure of afterload in the heart?

    <p>Systolic ventricular wall stress</p> Signup and view all the answers

    What is the formula for mean blood pressure (MBP)?

    <p>MBP = CO X TPR</p> Signup and view all the answers

    In patients with hypertension, increased afterload is primarily due to what factor?

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

    What happens to stroke volume when afterload is increased, while preload and contractility are held constant?

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

    What is the formula for cardiac output (CO)?

    <p>CO = stroke volume * heart rate</p> Signup and view all the answers

    What controls heart rate in normal people?

    <p>Sympathetic and parasympathetic nervous systems</p> Signup and view all the answers

    What effect does increased sympathetic nerve activity have on heart rate?

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

    What is the formula for calculating systolic ventricular wall stress?

    <p>S = (P x r) / 2 Th</p> Signup and view all the answers

    What happens to the velocity of muscle fiber shortening when afterload is increased?

    <p>Velocity of muscle fiber shortening decreases</p> Signup and view all the answers

    Which of the following is true about congestive heart failure (CHF)?

    <p>CHF is characterized by the inability of the heart to pump sufficient blood</p> Signup and view all the answers

    What is the result of decreased parasympathetic nerve activity near the SA node?

    <p>Increased frequency of action potentials</p> Signup and view all the answers

    What happens to stroke volume, cardiac output, and blood pressure when the time available for ventricular filling is reduced?

    <p>They decrease</p> Signup and view all the answers

    What is the primary cause of congestive heart failure (CHF)?

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

    What is the effect of increased end-diastolic volume (EDV) on the pressure-volume loop?

    <p>Dilated ventricles</p> Signup and view all the answers

    What is the characteristic of the failing cardiac myocytes in congestive heart failure (CHF)?

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

    What is the relationship between heart rate and time for ventricular filling?

    <p>Inverse relationship</p> Signup and view all the answers

    What happens to the pressure generating capability of the ventricle as it dilates?

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

    What is the result of increased end-diastolic pressure (EDP)?

    <p>Systemic edema</p> Signup and view all the answers

    What is the effect of increased exercise intensity on cardiac output?

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

    Which of the following is a cause of increased afterload in patients with hypertension?

    <p>A and B</p> Signup and view all the answers

    What happens to stroke volume when afterload is increased?

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

    Why does decreased stroke volume occur when afterload is increased?

    <p>Stroke volume is reduced because increased afterload reduces the velocity of muscle fiber shortening and the velocity by which the blood is ejected.</p> Signup and view all the answers

    Which of the following can be used to assess afterload in the heart?

    <p>All of the above</p> Signup and view all the answers

    Which of the following represents the pressure which the ventricle must overcome to begin ejection in the heart?

    <p>The diastolic pressure</p> Signup and view all the answers

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