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Questions and Answers
What is the formula for calculating stroke volume?
What is the formula for calculating stroke volume?
What is the normal range for ejection fraction (EF)?
What is the normal range for ejection fraction (EF)?
During tachycardia, how is the time for ventricular filling affected?
During tachycardia, how is the time for ventricular filling affected?
What is a characteristic of the third heart sound (S3)?
What is a characteristic of the third heart sound (S3)?
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Which condition is commonly associated with the fourth heart sound (S4)?
Which condition is commonly associated with the fourth heart sound (S4)?
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What does a decreased ejection fraction typically indicate?
What does a decreased ejection fraction typically indicate?
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At what point in the cardiac cycle is the end diastolic volume typically reached?
At what point in the cardiac cycle is the end diastolic volume typically reached?
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What term describes the volume of blood in each ventricle at the end of diastole?
What term describes the volume of blood in each ventricle at the end of diastole?
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What causes the closure of the mitral and tricuspid valves during the cardiac cycle?
What causes the closure of the mitral and tricuspid valves during the cardiac cycle?
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What is the primary characteristic of isovolumetric ventricular contraction?
What is the primary characteristic of isovolumetric ventricular contraction?
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How is the first heart sound (S1) generated?
How is the first heart sound (S1) generated?
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Which part of the cardiac cycle corresponds with the production of heart sound S2?
Which part of the cardiac cycle corresponds with the production of heart sound S2?
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What happens to the time spent in diastole during increased heart rates?
What happens to the time spent in diastole during increased heart rates?
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How much blood typically remains in the ventricles at the end of ventricular systole?
How much blood typically remains in the ventricles at the end of ventricular systole?
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Which of the following statements about the third heart sound is false?
Which of the following statements about the third heart sound is false?
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What leads to the heart sound S4 during the cardiac cycle?
What leads to the heart sound S4 during the cardiac cycle?
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During which phase do the aortic and pulmonary valves open?
During which phase do the aortic and pulmonary valves open?
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What primarily maintains the closure of the AV valves during isovolumetric relaxation?
What primarily maintains the closure of the AV valves during isovolumetric relaxation?
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Which event directly initiates the contraction in the ventricles?
Which event directly initiates the contraction in the ventricles?
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What is the typical duration of the complete cardiac cycle at a heart rate of 75 beats per minute?
What is the typical duration of the complete cardiac cycle at a heart rate of 75 beats per minute?
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What is the end systolic volume in the left ventricle?
What is the end systolic volume in the left ventricle?
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Which phase of the cardiac cycle corresponds to atrial systole contributing 20-30% of ventricular filling?
Which phase of the cardiac cycle corresponds to atrial systole contributing 20-30% of ventricular filling?
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What happens to the semilunar valves during rapid ventricular filling?
What happens to the semilunar valves during rapid ventricular filling?
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The a wave in atrial pressure waves corresponds to which event?
The a wave in atrial pressure waves corresponds to which event?
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What is the mean aortic pressure during the cardiac cycle?
What is the mean aortic pressure during the cardiac cycle?
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Which of the following is characteristic of the right atrium's pressure compared to the left atrium?
Which of the following is characteristic of the right atrium's pressure compared to the left atrium?
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How much blood does the stroke volume typically pump out per ventricle per beat?
How much blood does the stroke volume typically pump out per ventricle per beat?
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What occurs to the intraventricular pressures during the volume increase phase?
What occurs to the intraventricular pressures during the volume increase phase?
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What is the pressure range for the right ventricle during systole?
What is the pressure range for the right ventricle during systole?
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Which pressure is significantly lower on the right side of the heart compared to the left side?
Which pressure is significantly lower on the right side of the heart compared to the left side?
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Study Notes
Cardiac Cycle
- The cardiac cycle is divided into two phases: systole (contraction and emptying) and diastole (relaxation and filling).
- Systole is initiated by the spread of excitation across the heart.
- Diastole follows repolarization of the cardiac musculature.
- The cardiac cycle takes approximately 0.8 seconds when the heart rate is 75 beats per minute.
- Atria and ventricles have separate cycles of systole and diastole.
Atrial Systole
- Atrial systole is caused by atrial depolarization.
- Ventricles are relaxed during this phase.
- AV valves are open during atrial systole because atrial pressure exceeds ventricular pressure.
- Ventricles are passively filled with blood before atrial systole.
- Atrial systole further increases ventricular volume (final 10-30% of blood volume).
- Atrial pressure exceeds ventricular pressure throughout atrial contraction, keeping AV valves open.
- Atrial systole ends with ventricles maximally filled with blood, called End Diastolic Volume (EDV) which is about 120 ml.
- Atrial pressures fall after systole.
- A heart sound (S4) may be produced during atrial contraction if the ventricle is stiff.
Isovolumetric Ventricular Contraction
- Initiated by ventricular depolarization (QRS complex on the ECG).
- Myocytes contract, causing a rapid increase in ventricular pressure.
- Mitral and tricuspid valves close, creating the first heart sound (S1).
- S1 may be split if the mitral valve closes before the tricuspid valve.
- Papillary muscles contract, pulling on chordae tendinae to keep AV valves closed.
- Myocyte contraction leads to rapid rise in pressure, but no change in ventricular volume as all valves are closed.
Ventricular Systole: Rapid Ejection Phase
- Ventricular pressures exceed aortic and pulmonary artery pressures.
- Aortic and pulmonary valves open, allowing blood to flow rapidly into arteries, then with reduced velocity.
- Ventricular volumes decrease as blood is ejected.
Isovolumetric Ventricular Relaxation
- Ventricles begin to relax after rapid ejection.
- Intraventricular pressures fall below aortic and pulmonary artery pressures.
- Aortic and pulmonary valves close, creating the second heart sound (S2).
- All valves are closed again for a short period, while ventricles relax.
- This is when End Systolic Volume (ESV) is reached- the volume of remaining blood in the ventricle (around 50 ml in the left ventricle).
Rapid Ventricular Filling
- Ventricles continue to relax, and ventricular pressures fall below atrial and pulmonary artery pressures.
- Atria are maximally filled passively via venous return.
- Mitral and tricuspid valves open.
- Rapid inflow of blood into the ventricles occurs.
- The heart sound S3 may be heard.
Reduced Filling of Ventricles
- Corresponds with atrial systole, contributing to 20-30% of ventricular filling.
- Intraventricular pressures rise as volume increases.
- Aortic and pulmonary artery pressures fall as blood moves further into circulation.
Wiggers Diagram
- Provides a visual representation of the pressure and volume changes that occur during the cardiac cycle.
Cardiac Pressures
- Right-sided heart pressures are much lower than left-sided pressures, aiding blood flow.
Atrial Pressure Waves
- a wave: Represents atrial contraction.
- c wave: Ventricular contraction/ systole causes the A-V valve to bulge upward, increasing intra-atrial pressure.
- v wave: The peak of passive filling of the atria (very full atria). Opening of the AV valve leads to a pressure drop after the v-wave peak.
Volumes and Definitions
- Stroke Volume (SV): The volume of blood pumped out by each ventricle per beat (approximately 70-80 ml).
- End Diastolic Volume (EDV): The volume of blood in each ventricle at the end of diastole (approximately 120-130 ml).
- End Systolic Volume (ESV): The volume of blood in each ventricle at the end of systole (approximately 50-60 ml).
Ejection Fraction (EF)
- The percentage of EDV ejected with each stroke.
- Calculated as (SV/EDV) x 100.
- A normal ejection fraction is approximately 60-65%.
- Indicates ventricular function.
Tachycardia and its Effect on the Cardiac Cycle
- During tachycardia (increased heart rate), both systole and diastole times decrease.
- Diastole length is shortened more significantly than systole length.
- This reduces the time for ventricular relaxation and filling.
Heart Sounds
- First Heart Sound (S1): Closure of the mitral and tricuspid valves.
- Second Heart Sound (S2): Closure of the aortic and pulmonary valves.
- Third Heart Sound (S3): Rapid filling of the ventricles (audible in children).
- Fourth Heart Sound (S4): Atrial systole (normally not audible).
Third Heart Sound (S3)
- Heard during rapid diastolic filling (early diastole).
- Best heard with the bell of the stethoscope.
- May be normal in individuals under 40 years old.
- Can also indicate congestive heart failure or valvular disease.
Fourth Heart Sound (S4)
- Heard in late diastole.
- Indicates a stiff, fibrotic, or thickened ventricle.
- Best heard with the bell of the stethoscope.
- May be a normal finding in children.
- May also indicate aortic stenosis, hypertrophic cardiomyopathy, or hypertension.
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