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Cardiac Output Tutorial and Concept Map

Cardiac Output is . the volume of blood that leaves each ventricle during each minutemeasured in milliliters (mL) per minute (min) or liters (L) per minutenormally around 5,000 mL (5 L) per minute (5,000 mL/min or 5 L/min). Cardiac output (CO) is directly affected byheart rate (HR), the number

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Cardiac Output Tutorial and Concept Map

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    1. Cardiac Output Tutorial and Concept Map J. Ellen Lathrop-Davis Community College of Baltimore County, MD

    2. Cardiac Output is … the volume of blood that leaves each ventricle during each minute measured in milliliters (mL) per minute (min) or liters (L) per minute normally around 5,000 mL (5 L) per minute (5,000 mL/min or 5 L/min)

    3. Cardiac output (CO) is directly affected by… heart rate (HR), the number of times the heart beats each minute; and stroke volume (SV), the amount of blood ejected during each beat

    4. Heart Rate is directly affected by factors called chronotropic agents (or factors). These factors may be positive or negative.

    5. Positive chronotropic agents… increase heart rate and include epinephrine, norepinephrine and beta agonists (e.g., isoproterenol).

    6. Negative chronotropic agents… decrease heart rate and include acetylcholine (ACh) and beta antagonists (e.g., propranolol).

    7. Stroke Volume is affected by … preload, contractility and afterload

    8. Preload … is the volume-dependent pressure exerted on the walls of the ventricles by the blood in them at the end of diastole (end diastolic volume; EDV); and stretches the myocardium so that the myofibers are lengthened before contraction resulting in a stronger contraction, up to a point (above which strength decreases), according to the Frank-Starling law of the heart.

    9. Preload is directly affected by… filling time and venous return

    10. Filling time is inversely related to heart rate; as heart rate increases, filling time decreases. Chronotropic agents affect filling time, thus they affect EDV. However, these agents may also affect contractility such that the effects on stroke volume are less straightforward.

    11. Venous return depends on how much blood returns to the heart, which is… affected by: blood volume, venous pressure and intrathoracic pressure

    12. Blood volume and venous pressure (which increases during venoconstriction [constriction of the veins]) directly affect venous return.

    13. Intrathoracic pressure (which decreases during inspiration and increases during expiration) inversely affects venous return.

    14. Contractility is… the ability to generate tension independent of the effects of preload and afterload affected by factors called inotropic agents

    15. Positive inotropic agents… increase contractility and epinephrine, norepinephrine and cardiac glycosides (e.g., digitalis)

    16. Negative inotropic agents… decrease contractility and include calcium channel blockers (e.g., verapamil).

    17. Afterload is… the amount of tension the ventricles need to generate in order to eject blood into the arteries directly affected by arterial blood pressure

    18. Afterload… inversely affects stroke volume; and directly affects the volume of blood left in the ventricles at the end of systole (end systolic volume; ESV)

    19. In Summary… Heart rate and stroke volume are the two factors that determine cardiac output. Each of these is affected by many factors. Chronotropic agents affect heart rate while inotropic agents affect contractility, which affects stroke volume. Some factors (e.g., epinephrine and norepinephrine) affect both.

    20. Cardiac Output Concept Map

    21. Answers to Questions If HR increases, what will happen to cardiac output? – Cardiac output increases. If SV decreases, what will happen to cardiac output? – Cardiac output is expected to decrease (note that heart rate can be increased to compensate). What effect will sympathetic nerve impulses have on heart rate? – The norepinephrine released will increase heart rate. What effect will parasympathetic nerve impulses have on heart rate? – The ACh released will decrease heart rate.

    22. Answers to Questions What effect will increased heart rate have on stroke volume (if other factors stay the same)? – Stroke volume will decrease (note that SV may be maintained if the cause of the increased heart rate also increases contractility). What effect will increased venous return have on EDV? – EDV will increase. What effect will blood loss have on EDV? EDV will decrease (note that the body has compensatory mechanisms to initially maintain SV when blood is lost).

    23. Answers to Questions What effect will inhaling more deeply have on venous return? – Venous return will increase because deeper inhalation lowers thoracic pressure more than normal. What effect will epinephrine have on stroke volume? – Stroke volume will increase due to the increased contractility.

    24. Answers to Questions What effect will blocking calcium channels have on stroke volume? – Stroke volume will decrease. What effect will hypertension have on afterload? – Afterload will increase. What effect will hypertension have on stroke volume? Stroke volume will decrease (and the heart will have to work harder to eject blood).

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