Cardiac Output, Stroke volume, EDV, ESV, Ejection Fraction

Summary

Cardiac 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

00:00

💓 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).

Keywords

💡Cardiac Output

Cardiac output refers to the volume of blood pumped by each ventricle of the heart per minute. It is a critical measure of the heart's performance and is central to the video's theme of understanding how the heart functions. The script explains that it is the product of stroke volume and heart rate, and its increase during physical exercise illustrates the heart's adaptability to meet the body's demands.

💡Stroke Volume

Stroke volume is the amount of blood pumped with each heartbeat. It is a key component in calculating cardiac output. The script uses the example of a ventricle ejecting 60ml out of 100ml to demonstrate stroke volume, highlighting its importance in the heart's pumping mechanism.

💡Heart Rate

Heart rate is the number of times the heart beats per minute. It is essential for understanding how the heart responds to various conditions, such as during physical activity, to increase cardiac output. The script mentions that an increase in heart rate results in increased cardiac output.

💡Ejection Fraction

Ejection fraction is the percentage of blood that the heart's ventricle pumps out with each beat, expressed as a percentage of the end-diastolic volume. The script provides the example of a ventricle with an ejection fraction of 60%, emphasizing its role in assessing the heart's efficiency.

💡End-Diastolic Volume (EDV)

End-diastolic volume is the amount of blood in the ventricle at the end of the diastolic phase, just before it contracts. The script uses EDV as a reference point to calculate stroke volume, noting that it is typically about 100ml in a typical example.

💡End-Systolic Volume (ESV)

End-systolic volume is the remaining volume of blood in the ventricle after it has contracted. The script explains that ESV is the difference between EDV and the volume of blood ejected, which in the example is 40ml, indicating the efficiency of the heart's contraction.

💡Contractility

Contractility is the inherent ability of the heart muscle to contract and is a measure of its strength. The script relates contractility to the force of the heart's contraction, stating that greater contractility results in a higher ejection of blood.

💡Preload

Preload refers to the initial stretching of the heart muscle before it contracts, which is related to the end-diastolic volume. The script uses the analogy of a balloon to explain preload, indicating that the more the ventricle is filled, the greater the force of contraction due to the Frank-Starling mechanism.

💡Afterload

Afterload is the resistance against which the ventricle must pump blood, including vascular pressure and any damage to the valves. The script explains that afterload affects the amount of blood ejected by the heart, with higher afterload making it more difficult for the heart to pump blood effectively.

💡Vascular Pressure

Vascular pressure is the pressure within the blood vessels that the heart must overcome to eject blood. The script mentions that in conditions like hypertension, higher vascular pressure increases afterload, which can reduce the amount of blood ejected by the heart.

💡Valve Stenosis

Valve stenosis is a condition where the heart valves become narrowed, increasing resistance to blood flow. The script uses valve stenosis as an example of how damage to the valves can increase afterload and lead to lower blood output.

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.