Class 4 Cardiac Output and Volumes

Cardiac Output

-          The volume of blood pumped by the heart each minute and is measured in liters per minute. Cardiac output is determined by this equation CO = SV x HR

Stroke Volume

-          The amount of blood ejected from the heart with each beat and heart rate (HR) is the number of beats per minute. Stroke volume is expressed in mL/beat, and heart rate is beats/min

2 ways to alter Cardiac Output

-          Change stroke volume

-          Change heart rate

End Diastolic Volume (EDV)

-          Volume of blood left in heart at the end of systole

-          When the ventricle contracts during systole, not all blood is ejected. Amount that remains behind after contraction is ESV

End Systolic Volume (ESV)

-          Volume of blood left in heart at the end of systole

-          When the ventricle contracts during systole, not all blood is ejected. Amount that remains behind after contraction is ESV

How heart rate affects filling time

-          At lower heart rates the ventricles have plenty of time to fill with blood during diastole

-          As heart rate increases, diastolic filling time shortens, giving ventricles less time to fill before next contraction

-          Slower heart rate = more filling time = higher EDV

-          Faster heart rate = less filling time = lower EDV

Effect of Heart Rate on End Diastolic Volume (EDV)

-          Low to moderate heart rates, there is enough time for ventricles to fill so EDV stays about the same

-          At very high heart rates, diastole becomes very short, less time for it to fill. EDV decreases, stroke volume depends on EDV, so stroke volume also decreases

Measuring Hearts Pumping Performance

-          To understand how well heart is pumping you need to use two measurements: ejection fraction and cardiac reserve

-          Together they tell how efficiently the heart pumps blood and how well it can respond when body demands increase

Ejection Fraction

-          Describes the percentage of blood pumped out of a ventricle with each heartbeat

-          Most of the time EF refers to the right ventricle

-          During diastole left ventricle fills w blood, during systole it contracts and ejects some of that blood into the aorta

-          EF tells us how much of the blood that filled the left ventricle is actually pumped out

How EF is calculated

-          Ejection fraction =( Stroke Volume/ End Diastolic Volume) ( 100%)

-          Ex: if the ventricle fills with 120 mL of blood and pumps out 70mL, then:

-          EF = (70/120) x 100% = 58%

-          A normal left ventricular fraction is typically 55-70%

-          Low EF suggests heart is not pumping efficiently and may be seen in conditions like heart failure

-          High EF is less common but may occur in certain diseases such as hypertrophic cardiomyopathy

Cardiac Reserve

-          Describes heart’s ability to increase its output when the body needs more blood (exercise, stress, illness)

-          At rest cardiac output is about 5 L/min in a typical adult

-          During exercise can increase to 20 L/min or more

-          Difference between resting output and maximum output is the hearts cardiac reserve healthy heart has large cardiac reserve, diseased heart has a reduced cardiac reserve

The Frank Starling Law of the Heart

-          Describes how heart automatically adjusts how strongly it contracts based on how much blood fills it out

-          Explains the relationship between ventricular filling and the force of contraction

-          The more the heart fills with blood during diastole, the more forcefully it contracts during systole

The Frank Starling Law describes the relationship between ?

Ventricular filling and force of contraction

According to the Frank–Starling mechanism, what happens when venous return increases in a healthy heart?

Ventricular contraction becomes stronger

Why does increased ventricular filling lead to a stronger contraction?

Sarcomeres are stretched to an optimal length, allowing more cross-bridges

Venous Return

-          The amount of blood that flows back to the heart through the veins

-          Matters bc the heart cannot pump blood it doesn’t receive

-          When VR increases, heart fills w more blood, cardiac output can increase

-          When VR decreases, less blood fills the heart, and cardiac output falls

- Factors that affect venous return: blood volume/ venous tone

• Blood volume increases → venous return __________ → cardiac output _______.

increases, increases

• Blood volume decreases → venous return __________ →cardiac output ________.

decreases, decreases

• Veins constrict (increased venous tone) → push _____ blood towards the heart → venous return________ → cardiac output _________

more, increases, increases

• Veins dilate (decreased venous tone) → push ______ blood towards the heart → venous return___________ → cardiac output __________

less, decreases, decreases

Preload

-          Describes how much ventricular walls are stretched right before they contract

-          Preload depends on how much blood fills the ventricle right before contraction

-          This volume is the end diastolic volume (EDV)

-          Amount of stretch ventricular wall has right before it contracts

-          Less stretch = weaker contraction

-          Heart rate can also impact preload, ventricles have less time to fill, less preload, weak contraction

End-diastolic volume (EDV) increases → ventricle wall stretch _______ → preload ______ → cardiac output ______

increases, increases, increases

. Venous return increases → EDV ______ → ventricle wall stretch _______ → preload _________ → cardiac output ________

increases, increases, increases, increases

Venous return decreases → EDV ______ → ventricle wall stretch _______→ preload ________ → cardiac output ________

decreases, decreases, decreases, decreases

. Fast heart rate → EDV ______ → ventricle wall stretch ______→ preload ______→ cardiac output _______

decreases, decreases, decreases, decreases

. Slower heart rate → EDV ______ → ventricle wall stretch _______ → preload _______ → cardiac output_______

increases, increases, increases, increases

Afterload

-          the pressure the heart has to push against to pump blood out

-          mostly depends on the pressure in the aorta and rest of systemic arteries

-          if pressure is high, left ventricle has to work harder to open aortic valve and push blood forward

-          if pressure is low, blood flows out more easily

-          like trying to open a door and someone is pushing against it, more pushback = increased afterload, less pushback = decreased afterload

higher afterload = ____ to eject blood = ____ stroke volume

harder, lower

lower afterload = _____ ejection = _____ stroke volume

easier, higher

How Venous Return Affects Cardiac Volumes

-          primarily affects end diastolic volume (EDV)

-          venous return increases = more blood returns to the heart = more blood fills the ventricles during diastole ( this is the edv)

-          venous return decrease = less blood fills ventricles = EDV decreases

How Preload Affects Cardiac Volumes

-          primarily affects the end systolic volume (ESV) and stroke volume (SV). And is mainly determined by end diastolic volume (ESV)

-          EDV increases = preload increases = stronger contraction = stroke volume increases = amount of blood left in ventricle (EDV) decreases

-          EDV decreases = preload decreases weaker contraction = stroke volume decreases = esv decreases

How Afterload Affects Cardiac Volumes

-          Primarily affects stroke volume (SV) and end systolic volume (ESV). Afterload does not affect end diastolic volume (EDV) nor is it affected by it

-          Afterload increases = stroke volume decreases = end systolic volume increases

-          Afterload decreases = stroke volume increases = end systolic volume decreases

1. Which statement best defines stroke volume?

A. The total blood pumped by the heart each minute

B. The volume of blood remaining after ventricular contraction

C. The amount of blood in the ventricle before contraction

D. The amount of blood ejected from a ventricle with each beat

D

A ventricle fills with 150 mL of blood and has 90 mL remaining after systole. What is the stroke volume?

A. 60 mL

B. 90 mL

C. 150 mL

D. 240 mL

A

End-systolic volume (ESV) refers to:

A. Blood ejected during systole

B. Blood remaining in the ventricle after systole

C. Blood entering the ventricle during diastole

D. The percentage of blood ejected

B

If EDV increases while ESV remains constant, stroke volume will:

A. Decrease

B. Stay the same

C. Increase

D. Drop to zero

C

Which situation is most likely to reduce end-diastolic volume (EDV)?

A. Moderate exercise

B. Slower heart rate

C. Increased venous return

D. Extremely rapid heart rate

D

Why does EDV usually remain stable at low to moderate heart rates?

A. Diastolic filling time is sufficient

B. Afterload decreases automatically

C. Stroke volume is fixed

D. Ejection fraction increases

A

At very high heart rates, stroke volume may fall primarily because:

A. Systole shortens too much

B. Diastole shortens, limiting filling

C. Contractility decreases

D. Blood pressure collapses

B

A low ejection fraction most directly indicates:

A. Poor ventricular filling

B. Inefficient ventricular pumping

C. Excessive venous return

D. High cardiac reserve

B

Cardiac reserve is best defined as:

A. The heart’s resting cardiac output

B. The heart’s maximum stroke volume

C. The difference between resting and maximal cardiac output

D. The percentage of blood ejected per beat

C

The Frank–Starling Law explains how the heart:

A. Adjusts force of contraction based on venous return

B. Increases heart rate during exercise

C. Reduces afterload during systole

D. Controls blood pressure

A

Increased ventricular filling leads to a stronger contraction because:

A. Heart rate increases automatically

B. More calcium enters from sympathetic nerves

C. Afterload is reduced

D. Sarcomeres are stretched to a more optimal length

D

. According to the Frank–Starling mechanism, increased venous return will initially:

A. Increase EDV and stroke volume

B. Increase afterload

C. Decrease preload

D. Decrease ejection fraction

A

Which change would increase preload?

A. Decreased venous return

B. Increased heart rate

C. Reduced blood volume

D. Increased venous return

D

Preload is most closely related to which variable?

A. End-diastolic volume

B. End-systolic volume

C. Afterload

D. Heart rate

A

Venous constriction increases cardiac output because it:

A. Decreases afterload

B. Increases venous return

C. Slows heart rate

D. Reduces ventricular pressure

B

Afterload is best described as:

A. Ventricular wall stretch before contraction

B. The force of ventricular contraction

C. Resistance the ventricle must overcome to eject blood

D. Blood volume returning to the heart

C

Increased systemic blood pressure will most directly:

A. Increase afterload

B. Decrease preload

C. Increase EDV

D. Increase cardiac reserve

A

Which change would most likely decrease afterload?

A. Aortic valve stenosis

B. Systemic vasodilation

C. Increased blood viscosity

D. Elevated arterial pressure

B

Which variable primarily determines end-diastolic volume (EDV)?

A. Venous return

B. Afterload

C. Ejection fraction

D. Contractility

A

Increased afterload will tend to cause which change?

A. Decreased ESV

B. Increased EDV

C. Increased ESV

D. Increased preload

C

Increased preload typically results in:

A. Decreased stroke volume

B. Increased stroke volume

C. Increased afterload

D. Decreased EDV

B