Cardiac Output, Stroke volume, EDV, ESV, Ejection Fraction
Summary
TLDRCardiac output, the volume of blood pumped per minute, is determined by stroke volume and heart rate. An increase in either raises cardiac output, as seen during exercise. The heart doesn't fully eject its blood; ejection fraction is typically 60%. Stroke volume is influenced by contractility, preload, and afterload. Preload, analogous to a balloon's stretch, affects the force of contraction, while afterload, including vascular pressure and valve damage, represents the resistance the ventricles must overcome to pump blood.
Takeaways
- 💓 Cardiac output is the volume of blood pumped per ventricle per minute, calculated by multiplying stroke volume and heart rate.
- 🏃♂️ An increase in either stroke volume or heart rate leads to an increase in cardiac output, which is essential during physical activities.
- 🚫 Ventricles do not eject all the blood during one heartbeat, with an average ejection fraction of 60%.
- 🔢 The end-diastolic volume (EDV) is the amount of blood in a ventricle at the end of its load, typically around 100ml.
- 🔄 The end-systolic volume (ESV) is the remaining blood in the ventricle after contraction, which is 40ml in the given example.
- ➖ Stroke volume is determined by subtracting ESV from EDV and is influenced by three main factors.
- 💪 Contractility is the force of the heart muscle contraction, with stronger contractions ejecting more blood.
- 🎈 Preload is associated with EDV and represents the stretch of cardiac myocytes at the end of ventricular filling, affecting the force of contraction.
- 🚫 Afterload is the resistance the ventricle faces to eject blood, including vascular pressure and valve conditions.
- 🌡 High vascular pressure, as in hypertension, increases afterload, making it harder for the heart to eject blood.
- 🛠️ Valve damage, such as stenosis, also increases afterload and can reduce the amount of blood ejected by the heart.
Q & A
What is cardiac output?
-Cardiac output is the volume of blood pumped by each ventricle of the heart in one minute, calculated as the product of stroke volume and heart rate.
What is stroke volume and how is it related to cardiac output?
-Stroke volume is the amount of blood pumped in one heartbeat. It directly affects cardiac output, as cardiac output is the product of stroke volume and heart rate.
How does heart rate influence cardiac output?
-Heart rate, which is the number of beats in one minute, influences cardiac output. An increase in heart rate results in increased cardiac output, and a decrease would result in decreased output.
What happens to cardiac output during physical exercise?
-During physical exercise, the heart beats faster to meet the body's increased demand for blood, thus increasing cardiac output.
Why don't ventricles eject all the blood they contain in one beat?
-Ventricles do not eject all the blood due to the presence of an end-systolic volume (ESV), which is the remaining volume of blood in the ventricle after contraction.
What is the ejection fraction and how is it calculated?
-The ejection fraction is the percentage of blood that is ejected from the ventricle during contraction. It is calculated as (end-diastolic volume - end-systolic volume) / end-diastolic volume.
What is the end-diastolic volume (EDV) and its significance?
-End-diastolic volume (EDV) is the volume of blood in the ventricle at the end of its filling phase, before contraction. It is significant because it influences the preload and, through the Frank-Starling mechanism, the force of contraction.
What is preload in the context of cardiac function?
-Preload refers to the degree of stretch of cardiac myocytes at the end of ventricular filling, often represented by the end-diastolic volume. It affects the force of the heart muscle contraction.
What is the Frank-Starling mechanism and how does it relate to preload?
-The Frank-Starling mechanism states that the greater the stretch of the heart muscle (preload), the greater the force of contraction, allowing the heart to pump more blood with each beat.
What is afterload and how does it affect the heart's ability to eject blood?
-Afterload is the resistance the ventricle must overcome to eject blood, including vascular pressure and any damage to the valves. Increased afterload, such as in hypertension or valve stenosis, makes it more difficult for the heart to eject blood.
How does hypertension affect cardiac output?
-In hypertension, the higher vascular pressure increases afterload, making it more difficult for the heart to open the aortic and pulmonary valves, which can result in reduced cardiac output.
Outlines
💓 Cardiac Output Basics
Cardiac output is defined as the volume of blood pumped by one ventricle per minute, calculated by multiplying stroke volume (blood per heartbeat) by heart rate (beats per minute). It increases with higher stroke volume or heart rate and is crucial during physical activity. The ventricles do not fully eject their blood; typically, an ejection fraction of 60% is observed, with 100ml as end-diastolic volume (EDV) and 40ml as end-systolic volume (ESV). Stroke volume is influenced by contractility (force of heart muscle contraction), preload (stretch of cardiac myocytes, often approximated by EDV), and afterload (resistance to blood ejection, including vascular pressure and valve damage).
Mindmap
Keywords
💡Cardiac Output
💡Stroke Volume
💡Heart Rate
💡Ejection Fraction
💡End-Diastolic Volume (EDV)
💡End-Systolic Volume (ESV)
💡Contractility
💡Preload
💡Afterload
💡Vascular Pressure
💡Valve Stenosis
Highlights
Cardiac output is defined as the volume of blood pumped by each ventricle per minute.
It is calculated by multiplying stroke volume and heart rate.
Stroke volume is the amount of blood pumped in one heartbeat.
Heart rate is the number of heartbeats in a minute.
An increase in either stroke volume or heart rate leads to increased cardiac output.
Cardiac output increases during physical exercise to meet the body's higher demand for blood.
Ventricles do not eject all the blood during one beat, with an ejection fraction typically around 60%.
End-diastolic volume (EDV) is the amount of blood in a ventricle at the end of its load, typically around 100ml.
End-systolic volume (ESV) is the remaining blood in the ventricle after contraction, about 40ml.
Stroke volume is determined by the difference between EDV and ESV.
Contractility is the force of the heart muscle contraction, affecting the amount of blood ejected.
Preload is related to the stretch of cardiac myocytes at the end of ventricular filling, often represented by EDV.
The Frank-Starling mechanism explains the relationship between stretch and force of contraction.
Afterload is the resistance the ventricle faces when ejecting blood, including vascular pressure and valve damage.
Vascular pressure must be overcome for the aortic and pulmonary valves to open.
High blood pressure increases afterload, potentially reducing the amount of blood ejected.
Valve damage, such as stenosis, increases resistance and can decrease cardiac output.
Transcripts
Cardiac output is the amount of blood pumped by each ventricle in one minute.
It is the product of stroke volume – the amount of blood pumped in one heartbeat, and
heart rate – the number of beats in one minute.
An increase in either stroke volume or heart rate results in increased cardiac output,
and vice versa.
For example, during physical exercises, the heart beats faster to put out more blood in
response to higher demand of the body.
It is noteworthy that the ventricles do not eject all the blood they contain in one beat.
In a typical example, a ventricle is filled with about 100ml of blood at the end of its
load, but only 60ml is ejected during contraction.
This corresponds to an ejection fraction of 60%.
The 100ml is the end-diastolic volume, or EDV.
The 40ml that remains in the ventricle after contraction is the end-systolic volume, or
ESV.
The stroke volume equals EDV minus ESV, and is dependent on 3 factors: contractility,
preload, and afterload.
Contractility refers to the force of the contraction of the heart muscle.
The more forceful the contraction, the more blood it ejects.
Preload is related to the end-diastolic volume.
Preload, by definition, is the degree of stretch of cardiac myocytes at the end of ventricular
filling, but since this parameter is not readily measurable in patients, EDV is used instead.
This is because the stretch level of the wall of a ventricle increases as it’s filled
with more and more blood; just like a balloon - the more air it contains, the more stretched
it is.
According to the Frank-Starling mechanism, the greater the stretch, the greater the force
of contraction.
In the balloon analogy, the more inflated the balloon, the more forceful it releases
air when deflated.
Afterload, on the other hand, is the resistance that the ventricle must overcome to eject
blood.
Afterload includes 2 major components: - Vascular pressure: The pressure in the left
ventricle must be greater than the systemic pressure for the aortic valve to open.
Similarly, the pressure in the right ventricle must exceed pulmonary pressure to open the
pulmonary valve.
In hypertension for example, higher vascular pressures make it more difficult for the valves
to open, resulting in a reduced amount of ejected blood.
- Damage to the valves, such as stenosis, also presents higher resistance and leads
to lower blood output.
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