BSI: Pumping Action of the Heart

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re.pitt
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67384
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BSI: Pumping Action of the Heart
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2011-02-19 15:47:09
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BSI Heart Cardiovascular
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BSI: Spring 2011, Pumping Action of the Heart
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  1. What does a cardiac cycle refer to?
    Refers to the sequence of events (electrical and mechanical) occurring in the heart during a single beat.

  2. What is Systole and Diastole?
    Systole: Contraction phase of cardiac cycle

    Diastole: Relaxation phase of cardiac cycle
  3. What is the function of the Atria?
    When AV valves are open, most blood returning to atria pass right through to the ventricles (75% of blood). In other words, there is no contraction needed; this is passive filling.

    When atria do contract, they push more blood into ventricles (25%). This "tops off" the ventricles.

    Atria function to enhance the amount of blood in ventricles, which enhances ventricular pumping.

    The heart can function without atrial contraction.
  4. What is the function of the Ventricles?
    The right ventricle functions to pump blood through pulmonary circulation.

    The left ventricle functions to pump blood through systemic circulation.
  5. Are the ventricles ever empty?
    No...there is always some blood volume in the ventricles.
  6. How do the valves function?
    • Valves open and close passively
    • - Forward pressure gradient opens valves
    • - Backward pressure gradient closes valves

  7. What does papillary muscle do?
    Papillary muscle of AV valves prevent cusps from protruding into atria as ventricles contract.
  8. What happens if there is damage to chordae tendinae or papillary muscle?
    Damage to chordae tendinae or papillary muscle results in backward flow of blood as ventricles contract and could be lethal.
  9. Which valves have papillary muscle and chordae tendinae?
    Only Atrioventricular (AV) Valves, which includes the tricuspid and bicuspid/mitral valves.

    Semilunar valves DO NOT have chordae tendinae or papillary muscle.
  10. What are the phases of the cardiac cycle?
    • Atrial contraction
    • Ventricles begin to contract—period of isovolumetric contraction
    • - Pressure in ventricle begins to rise causing AV valve to close
    • - Moments later, pressure rises further and causes semilunar valves to open

    • Period of ejection
    • As ventricular pressure rises above arterial pressure, blood is pushed out of ventricle as semilunar valves open

    • Period of isovolumetric relaxation
    • -Ventricles begin to relax; pressure begins to drop with ventricle
    • - As pressure drops below arterial pressure, semilunar valves close
    • - Ventricles continue to relax and eventually the pressure drops low enough that AV valves open again allowing ventricles to fill again

    Ventricular filling

  11. Systole
    Systole: Contraction phase of cardiac cycle
  12. Diastole
    Diastole: Relaxation phase of cardiac cycle
  13. End diastolic volume (EDV)
    The volume of blood in the ventricle at the end of diastole (110 ml).

    In other words, EDV is the volume in the ventricle right before the ventricle contracts.

    This is considered the preload (the stretched condition of the heart at the end of diastole).
  14. End systolic volume (ESV)
    The volume of blood in the ventricle at the end of systole (40 ml).

    In other words, ESV is the volume in the ventricle right after the ventricle contracts (which is the end of ventricle ejection or during isovolumetric relaxation).

    Note that because the ESV has a volume of 40 ml, the ventricle is never empty.
  15. Stroke volume (SV)
    The volume of blood pumped out of the left ventricle per contraction (70 ml).

    Determined by preload, afterload, and contractility.

    • Formula: SV = EDV - ESV
    • SV = 110 ml - 40 ml
    • SV = 70 ml
  16. What three things determine the stroke volume?
    • 1) preload
    • 2) afterload
    • 3) contractility
  17. Ejection fraction
    The fraction of EDV that was pumped out of the left ventricle per contraction (60%).

    • Formula: EF = (SV/EDV) x 100
    • EF = [(SV = EDV- ESV)/EDV] x 100
    • EF = [(SV = 110 - 40)/110] x 100
    • EF = [70/110] x 100
    • EF = 63.6%
    • EF = round to ~60%
  18. Cardiac output
    The amount of blood pumped out of the left ventricle per minute.

    Cardiac output = heart rate x stroke volume (5000 ml).

    • Formula: CO = HR x SV
    • CO = HR x SV
    • Given HR = 60 beats/min
    • CO = HR x (EDV - ESV)
    • CO = 60 x (110 ml - 40 ml)
    • CO = 4,200 ml/min
    • Note: CO is measured in ml per MINUTE...not per beat!

    Cardiac output is one way to measure how efficient the heart is. High cardiac output is related to an increase in heart disease, heart failure and stroke. The harder the heart has to work when it is resting (i.e. not exercising), the less efficient it is.
  19. Venous Return
    The amount of blood returned to the right atrium.

    Note: Venous Return is measured in ml per MINUTE...not per beat!
  20. Preload
    The pressure stretching the chamber of the heart.

    The end diastolic volume is primary determinant of preload.

    Frank-Starling Mechanism: as the muscle stretches, sarcomeres approach optimal length leading to greater strength of contraction.
  21. What is the primary determinant of preload?
    End Diastolic Volume (EDV)
  22. Why does stretching the sarcomeres increase strength of contraction?
    Because increased stretching optimizes the overlap of actin and myosin. Therefore, it creates a situation which increases or maximizes the number of cross bridges.

    In other words, the more you increase the stretch of sarcomeres, the more you contract with greater force.
  23. Afterload
    The pressure that the chamber of the heart has to overcome in order to eject blood.

    • For the left ventricle:
    • afterload = aortic pressure = diastolic pressure.

    Diastolic pressure in a normal healthy individual is 80. For patients with high blood pressure, they may have to overcome measures of 100 or greater to overcome afterload.

    Afterload will decrease stroke volume.
  24. What pressure does the ventricle have to overcome in order to eject blood?
    Afterload. The ventricle has to overcome the pressure of the aorta in order to eject blood because the valve has to open. This pressure is known as afterload.
  25. Contractility
    The intrinsic property of cardiac muscle to produce tension.

    A change in the force of contraction at a constant end-diastolic fiber length reflects a change in contractility.
  26. In most cases, what is the primary determinant of contractility?
    The ability of a fiber to produce force at any given length in most cases has to do with the amount of intracellular Ca2+ present.

    Therefore, most of the time, the primary determinant of contractility is the amount of intracellular Ca2+.

    However, other things can affect contractility. For example, a structural problem could interfere with cross bridging and affect contractility.
  27. Chronotropic effect
    • Affecting heart rate
    • If you increase heart rate, you have a positive chronotropic effect.
  28. Inotropic effect
    Affecting contractility

    If you increase or decrease contractility, you affect ionotropic effect.
  29. Heart sounds
    Lub-dub

    1st sound (Lub): closing of AV valves

    2nd sound (Dub): closing of semilunar valves
  30. What other names do the heart sounds go by?
    Lub, the first sound, is sometimes called S1. Recall this sound is associated with the closing of AV valves.

    Dub, the second sound, is sometimes called S2. Recall this sound is associated with closing of semilunar valves.

    There is also an "S3" and "S4."

    S3 is associated with ventricular filling. If S3 is heard, it may or may not signify an abnormality.

    However, if you hear S4, there is almost always an abnormality with atrial contraction.
  31. What is an Electrocardiogram?
    An Electrocardiogram, also known as "ECG" or an "EKG" measures the electrical activity of the heart.

    • P wave
    • Atrial depolarization

    • QRS complex
    • Ventricular depolarization

    • T wave
    • Ventricular repolarization

  32. EKG: What does the P wave represent?
    Atrial depolarization
  33. EKG: What does the QRS complex represent?
    Ventricular depolarization
  34. EKG: What does the T wave represent?
    Ventricular repolarization
  35. Why doesn't atrial repolarization show up on the EKG?
    Atrial repolarization is usually hidden in the QRS complex. Therefore, most of the time it is not visible on an EKG.
  36. What point on the graph would represent EDV, ESV and SV?
    EDV: represented by the end of the first pink section. Recall that EDV is the volume of blood in the ventricle at the end of diastole (110 ml).

    ESV: represented at the end of the purple section. Recall ESV is the volume of blood in the ventricle at the end of systole (40 ml).

    SV: The difference between the EDV-ESV. Recall SV is the amount of blood pumped out of the left ventricle per contraction (70 ml).





  37. How do you calculate the Ejection Fraction? Use the following case study: Mrs. Jones has a heart rate of 85, a systolic pressure of 140 and diastolic pressure of 60, and an end diastolic volume of 110 and end systolic volume of 40. What is her cardiac output?
    Recall the Ejection fraction is the fraction of EDV that was pumped out of the left ventricle per contraction.

    Therefore, to find the Ejection Fraction:

    • Recall EF = (SV/EDV) x 100
    • EF = [(SV = EDV- ESV)/EDV] x 100
    • EF = [(SV = 110 - 40)/110] x 100
    • EF = [70/110] x 100
    • EF = 63.6%
  38. How do you calculate Cardiac Output (CO) if given Heart Rate (HR)? Use the following case study: Mrs. Jones has a heart rate of 85, a systolic pressure of 140 and diastolic pressure of 60, and an end diastolic volume of 110 and end systolic volume of 40. What is her cardiac output?
    • Recall SV = EDV- ESV = 110 - 40 = 70
    • Recall CO = HR x SV = 85 x 70 = 5950 mL/min
  39. Which two factors increase strength and contraction, but they do it by different mechanisms?
    Preload: the more you stretch the sarcomeres, the more you optimize the number of cross bridges, and therefore increase the force and strength and contraction.

    Contractility: Recall Ca2+ binds to troponin to move tropomyosin out of the way and exposes myosin, therefore increased intracellular Ca2+ would increase the number of cross bridges and therefore increase the strength and force of contraction.

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