Topic 4: Heart as a Pump & the Regulation of Cardiac Output

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jlyip89
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Topic 4: Heart as a Pump & the Regulation of Cardiac Output
Updated:
2014-01-10 01:02:06
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Heart Pump Cardiac Output
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systems 1
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systems 1. lecture 1.3
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  1. Cardiac output
    - def.
    - equation
    - normal CO
    volume of blood pumped by the heart per minute

    CO =HR x SV     [4-8 L/min]

    • HR: heart rate
    • SV: stroke volume
  2. Stroke Volume
    - def.
    - equation
    - normal SV
    volume of blood pumped out in one beat

    SV = EDV - ESV      [50-90 ml]

    • EDV: end diastole volume
    • ESV: end systole volume
  3. Ejection Fraction
    - def.
    - equation
    - normal EF
    percentage of blood that is pumped out each beat

    EF = SV / EDV    [55-70%]

    note: < 40% = heart failure
  4. Mean Arterial Pressure
    - def.
    - equation
    - normal mean arterial pressure
    • - mean of all the pulses over time
    • - describes average blood pressure

    MAP = DBP + (PP/3)    [85-105mmHg]       

    • DBP: diastole blood pressure ?
    • PP: Pulse Pressure
    • PP = Systolic – diastolic
  5. Total Peripheral Resistance
    - definition
    - aka
    - equation
    sum of the resistance of all peripheral vasculature in the systemic circulation (vs pulmonary circulation)

    aka systemic vascular resistance

    SVR = TPR =  (MAP - CVP) / CO

    • MAP: mean arterial pressure
    • CVP: cardiac venous pressure
    • CO: cardiac output
  6. 4 phases of the cardiac cycle

    -  which two phases are in systole and which two are in diastole?
    • 1. Ventricular Filling - diastole
    • 2. Isovolumetric Contraction - systole
    • 3. Ventricular Ejection - systole
    • 4. Isovolumetric Relaxation - diastole
  7. isovolumetric ventricular contraction
    - what occurs?
    - which valves are opened/closed?
    - systole or diastole?
    - ventricles contract with no corresponding volume change

    - both valves are closed

    - early systole
  8. Ventricular Ejection
    - what occurs?
    - which valves are open/closed?
    - diastole? systole?
    - all the blood is pumped out of the heart

    • - AV valve: closed
    • - aortic + pulmonary valves: open

    - systole
  9. isovolumetric relaxation
    - what occurs?
    - which valves open/close?
    - diastole? systole?
    - heart relaxes before it refills with blood

    - both valves are closed

    - early diastole
  10. Ventricular Filling
    - what occurs?
    - which valves open/close?
    - diastole? systole?
    - atria is relaxed as blood fills ventricles then you have atrial contraction

    • - AV valves: open
    • - aortic + pulmonary valves: closed

    - diastole
  11. pressure in pulmonary circulation vs systemic circulation
    Pulmonary circulation  pressures are about ¼ to 1/5 of those in the systemic circulation.
  12. blood flows from area of high to low pressure? or low to high pressure?
    blood flows form area of high pressure to low pressure
  13. cardiac output is influenced by???
    the amount of work done by the heart

    W = Force x Distance
  14. how can "cardiac work" can be determined/measured?
    • from the measured changes in chamber
    • volume to eject blood against the aortic pressure (or afterload)
  15. Stroke work
    - definition?
    - how to locate on PV-loop graph
    - the work performed by the heart during one beat

    • - area of the PV loop (larger the area, the
    • more work needed)
  16. Stroke Work Index
    - equation
    - what it tells you
    • STROKE WORK INDEX = stroke work / body
    • surface area

    - way to compare the amount of work being done from one individual to another, accounting for the fact that humans vary in size
  17. Cardiac Index
    - eq.
    cardiac index = CO/body surface area

    - accounts for the fact that humans vary in size
  18. How to measure stroke volume?
    - can be indirectly estimated via ultrasound echocardiography
  19. How to measure stroke work?
    hard to measure in humans, but very useful in assessing the metabolic demand
  20. Cardiac Output
    can be measured in a variety of ways including ultrasound or catheterizations

    • Catheterizations are the preferred
    • method when precision is needed since they can provide both pressures and flows within the heart and vessels
  21. The Cardiac Cycle tells you what
    The Cardiac Cycle relates the pressures in left atria, left ventricle (LV) and aorta to the LV volume, ECG, heart sounds and valve function
  22. cardiac cycles for right ventricle and pulmonary artery compared to left ventricle
    The cardiac cycle for the right ventricle (RV) and pulmonary artery is analogous, but at lower pressures
  23. what are the intrinsic factors in the regulation of cardiac output?
    Starling Pressure-Volume Relationship

    –Modulation of EDV, SV & Preload
  24. what are the (3) extrinsic factors in the regulation of cardiac output?

    - what do each modulate
    Contractility   - modulates ESV, SV

    Afterload  - also modulates ESV, SV

    Chronotropic   - modulates HR
  25. what are the 2 ways to increase cardiac output?
    • 1) increase HR
    • 2) increase SV
  26. 3 ways to increase stroke volume?
    - name whether each is intrinsic or extrinsic
    1) increase end-diastolic ventricular volume (intrinsic)

    2) increase activity of sympathetic nerves to heart (extrinsic)

    3) increase plasma epinephrine (extrinsic)
  27. 3 ways to increase heart rate?
    - name whether each is intrinsic or extrinsic
    1) decrease activity of parasympathetic nerves to heart (extrinsic)

    2) increase activity of sympathetic nerves to heart (extrinsic)

    3) increase plasma epinephrine (extrinsic)
  28. Frank-Starling Law of the Heart
    SV increases in response to an increase in the volume of blood filling the heart (the end diastolic volume) when all other factors remain constant.

    (instrinsic)
  29. What are the effects of changes in preload (Frank-Starling Law) of the heart?
    increasing preload (change in EDV), increases SV which increases CO
  30. How does sympathetic stimulation help increase CO?

    - what gets released?
    - what are the effects?
    release of norepinephrine and epinephrine in the sympathetic system (extrinsic)

    increases contractility (preload remain the same) --> decrease ESV --> increase SV --> increase CO
  31. How does the Force-Velocity curve change w/ increasing contractility (via sympathetic stimulation and release of nor-epinephrine)?

    - what accounts for these changes?
    curves will shift out and upward

    force increases bc the amt of Ca in the ST is increased from both the SR and Ca channels

    velocity of shortening increases since the myosin light chains are pohsphorylated to elicit faster crossbridge cycling
  32. Sympathetic stimulation (release of NE) of the heart _________ the maximal developed force
    and _________ the duration of the contraction.
    increases

    shortens
  33. What are the effects of increasing afterload in heart?
    An increased afterload prolongs the isovolumetric contraction phase and reduces the time for ejection

    • EDV remains the same
    • ESV increases
    • SV decreases (SV = EDV-ESV)
    • CO is reduced
  34. chronotropic regulation of the heart
    Pacemaker discharges from the SA node initiate the heart beat.

    - But the rate of discharge is modulated extrinsically via Chronotropic Regulation

    - The modulation of heart rate is the primary extrinsic factor utilized to modulate CO
  35. types of chronotropic regulation
    • 1) increase plasma epinephrine
    • 2) increase activity of sympathetic nerves to heart
    • 3) decrease activity of parasympathetic nerves to heart

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