Questions and Answers
Which of the following formulas is used to calculate stroke volume?
What is the normal value of ejection fraction?
What are the two factors that cardiac output depends on?
What is the effect of an increase in contractility on ejection fraction?
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How can cardiac output be increased?
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What are the three factors that affect stroke volume?
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What is the formula used to calculate left ventricular ejection fraction?
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What is the primary factor that influences end-diastolic volume and initial cardiac fiber length?
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According to the Frank-Starling Law, what is the relationship between end-diastolic volume and stroke volume?
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What is the effect of increased contractility on stroke volume?
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What is the term for the intrinsic ability of myocardial cells to develop force at a given cell length?
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What is the formula to calculate stroke volume?
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What is the effect of increased preload on stroke volume, according to the Frank-Starling Law?
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What is the term for the relationship between end-diastolic volume and stroke volume, as described by Otto Frank and Ernest Starling?
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What is the formula for stroke volume?
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What determines the preload?
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What is the optimal resting length for skeletal muscle?
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How does an increase in fiber length affect the contractile force of the heart?
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What is the relationship between fiber length and contractile force in cardiac muscle?
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What is the effect of preload on stroke volume?
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What is the normal resting fiber length of cardiac muscle compared to the optimal length?
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What is the primary effect of an increase in aortic blood pressure on stroke volume?
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What is the Anrep effect?
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What is the effect of sympathetic stimulation on contractility?
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What is afterload?
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What is the effect of an increase in intracellular calcium concentration on contractility?
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What is the effect of epinephrine on cardiomyocyte relaxation?
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What is the effect of increased afterload on end-systolic volume?
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What is the effect of an increase in aortic pressure on the Frank-Starling mechanism?
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What is the primary mechanism by which epinephrine increases contractility?
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Study Notes
Cardiac Output
- Cardiac output is the total volume of blood ejected by the left ventricle per unit time (mL/min).
- It depends on stroke volume and heart rate.
Stroke Volume
- Stroke volume is the volume of blood ejected out of the left ventricle during each systolic cardiac contraction.
- It is the difference between end-diastolic volume and end-systolic volume.
- Stroke volume (ml) = End-diastolic volume – End-systolic volume.
Ejection Fraction
- Ejection fraction is the fraction (%) of the end-diastolic volume that is ejected in one stroke volume.
- It describes the effectiveness of the ventricles in ejecting blood.
- Normally around 60% (0.6).
- It is an indicator of contractility.
Factors Affecting Stroke Volume
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Preload (End-Diastolic Volume/Fiber Length)
- Influenced by diastolic filling and venous return.
- The greater the extent of diastolic filling, the larger the end-diastolic volume, and the more the heart is stretched.
- The more the heart is stretched, the longer the initial cardiac fiber length before contraction.
- The increased length leads to a greater force of contraction and a greater stroke volume.
- Frank-Starling mechanism: The greater the heart muscle is stretched during filling, the greater is the force of contraction, and the greater the quantity of blood pumped into the aorta.
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Contractility or Inotropism
- Refers to the pumping ability of a ventricle.
- Intrinsic ability of myocardial cells to develop force at a given cell length.
- An increase in contractility leads to a more complete emptying of the ventricle during systole = DECREASE IN END SYSTOLIC VOLUME.
- Consequently, INCREASE IN STROKE VOLUME.
- Without the need to increase end-diastolic volume.
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Afterload
- Is the resistance that the ventricles must overcome to empty its content – The force opposing ejection.
- The afterload for the left ventricle is the aortic pressure.
- When aortic blood pressure increases, stroke volume decreases, and end systolic volume/pressure increases.
- Can also be raised by obstructions to flow (i.e. semilunar valve stenosis).
- Stroke volume decreases as afterload increases.
- The Anrep effect allows myocardium to compensate for an increased end-systolic volume and decreased stroke volume that occurs when aortic blood pressure increases.
Control of Cardiac Output
- Cardiac output can be increased only if stroke volume increases, heart rate increases, or both increase.
- To understand how the body controls cardiac output, we must understand how the body controls stroke volume and heart rate.
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Description
Understand the concepts of cardiac output, stroke volume, and ejection fraction in the context of cardiovascular physiology. Learn how to calculate stroke volume and its relationship with heart rate and end-diastolic and end-systolic volumes.