[Exam 1] Lecture 2: Venous Return, Cardiac Output Curve, Cardiac Cycle, Pressure Volume Loops Flashcards
What is the Reynolds Equation?
What is the Reynolds number?
A hypothetical number that is completely unitless.
What Reynolds number indicates turbulent flow?
> 2,000
What is turbulent flow?
Blood moving in all different directions, with wasted energy and potential clotting risk.
Turbulent flow can also include air
What factors increase the risk for turbulent flow?
- Elevated velocity
- Wide diameter
- Higher density
In which blood vessels is turbulent flow most likely to occur?
Why?
Large arteries close to the heart, such as the Aorta.
The arterial circulation has higher velocity than venous circulation.
What is the difference between density and viscosity?
Density is mass per volume, while viscosity refers to the thickness of a fluid.
Oil is more viscous than water but water is more dense than oil.
What happens to pressure in the arterial system when volume changes?
Pressure changes a lot when volume changes a little.
How does sympathetic stimulation affect arteries and veins?
Removing sympathetic stimulation lowers pressure more in arteries than in veins.
What is a pressure-volume loop?
It represents different pressures and volumes in the chambers of the heart during the cardiac cycle.
What is the end systolic volume (ESV) in a healthy heart?
50 mls, which is the volume left in the left ventricle after the last ejection.
What primarily drives the filling of the heart during phase 1?
Passive filling, dependent on preload.
What role do the atria play in ventricular filling?
They provide a small amount of additional volume just before the heart contracts.
10 mL/s
True or False: Turbulent flow is more likely to occur in veins than in large arteries.
False.
What happens to pressure in the venous system when volume is added?
Pressure changes only a little.
What happens to pressure when sympathetic stimulation is maximized?
It can significantly increase pressure in the arteries.
What is the typical volume of blood in a healthy heart’s left ventricle at the beginning of filling?
50 mls.
What is the effect of high velocity on turbulent flow risk?
Higher velocity increases the risk of turbulent flow.
What is the total amount of blood filling during phase one of the cardiac cycle?
70ccs
Only 10ccs of that is due to the atria in healthy individuals.
120 (lvedv) - 50 (ESV)
What role do the atria play in the filling of the ventricle for healthy individuals?
Minimal role
Atria are not necessary for filling; passive flow can fill the ventricle without atrial contraction.
In patients with heart problems, how important is atrial filling?
Very important
Atrial filling becomes crucial due to potential ventricular wall thickening or chamber size reduction | In Heart Failure, as much as 25% of ventricular filling.
What is the term used to describe the contraction of the atria that contributes to ventricular filling?
Atrial kick
In healthy individuals, the atrial kick is not significant.
At what point does diastole end in the cardiac cycle?
When the ventricle starts to contract
Diastole is primarily the filling phase.
During phase two of the cardiac cycle, what happens to the heart muscles?
The heart starts to contract
This leads to increased left ventricular pressure.
What happens to the mitral valve during phase two?
It closes
This occurs when left ventricular pressure exceeds left atrial pressure.
What do we call the phase where there is no change in intraventricular volume despite ventricular contraction?
Isovolumetric contraction
Both input (mitral) and output (aortic) valves are closed during this phase.
Phase 2
What is the period called when the left ventricular pressure exceeds the aortic pressure?
Period of ejection | Systole
This occurs during phase three.
How is stroke volume calculated?
End-diastolic volume - End-systolic volume
Example: 120 - 50 = 70ml.
What happens at the beginning of phase four of the cardiac cycle?
The aortic valve closes
This occurs when ventricular pressure is lower than aortic pressure.
What defines diastole in terms of cardiac cycle phases?
Starts when the aortic valve closes
This is at the end of phase three.
What is the typical peak systolic pressure during systole?
Peak pressure - 120 mmHg
This is when the heart is ejecting blood. Generated during phase three
What characterizes the pressure volume loop in terms of heart function?
It reflects the contractile state of the heart
Changes in position indicate different contractile strengths.
What occurs during the electrical event before changes in pressures in the ventricle?
Depolarization of muscle
This is followed by force generation, which has a slight delay.
What are the pressure conditions in the ventricle during filling?
Very low pressure
High pressure occurs during ejection.
What is the relationship between the QRS complex and ventricular pressure change?
QRS occurs before pressure changes
There is a slight delay as the electrical event allows calcium influx.
What happens to ventricular volume at the end of filling?
Peaks at about 120ccs
This volume is maintained until the heart starts to contract.
What does the graph illustrate regarding ventricular filling?
The graph illustrates the rapid filling of the ventricle over time, showing both EKG and blood pressure changes
The bottom axis represents time, making the graph useful for understanding events occurring at any instant.
What is the first third of Phase 1 in ventricular filling characterized by?
The first third of Phase 1 is characterized by rapid filling of the ventricle due to blood flooding in from the left atrium after the mitral valve opens
This occurs after a prolonged closure of the mitral valve, which allows blood to accumulate in the left atrium.
What occurs during the middle third of Phase 1?
A small amount of additional volume may enter from the atria at the end of this phase.
How does a stenotic mitral valve affect ventricular filling?
A stenotic mitral valve slows down the filling of the ventricle, requiring more time for adequate filling
If tachycardia occurs, cardiac output may be compromised due to insufficient filling time.
What is the ventricular volume just before the aortic valve opens?
The ventricular volume is approximately 120 cc just before the aortic valve opens
The volume decreases to about 50 cc during systole, indicating the amount of blood ejected.
Does blood ejection continue until the end of phase III?
Yes, blood ejection continues until the end of phase III, even if the amount ejected is decreasing
Many mistakenly believe ejection stops when aortic pressure peaks.
What is isovolumetric contraction?
Isovolumetric contraction is the phase where pressure increases without any change in volume
This occurs during phase II of the cardiac cycle.
What happens to atrial pressure during atrial contraction?
Atrial pressure increases during atrial contraction
This increase is caused by a portion of blood moving forward and some moving backward.
What happens to atrial pressure when the mitral valve closes?
Atrial pressure rises as blood returns to the heart, filling the atria with no outlet
This pressure increase continues until the AV valves open.
What is the normal right atrial pressure?
The normal right atrial pressure is zero
This applies to the right side of the heart.
What is the expected left atrial pressure for normal cardiac output?
The expected left atrial pressure for normal cardiac output is about 2 mmHg
This pressure allows the left side of the heart to output about 5L/min.
What is the primary function of heart valves?
Heart valves function as one-way gates that open and close based on pressure differences
They ensure unidirectional blood flow through the heart.
Fill in the blank: The mitral valve is also known as the _______.
[bicuspid valve]
True or False: The tricuspid valve is located in the middle of the heart.
True
What is the relationship between the left and right ventricular outputs?
The left and right ventricular outputs must be equal to maintain blood flow balance
This ensures there is no gain or loss of blood in the pulmonary circuit.
What happens to atrial pressure when the AV valves open?
Atrial pressure drops quickly when the AV valves open
This occurs due to the influx of blood into the ventricle.
What happens to venous return when right atrial pressure is elevated?
It decreases
Elevated right atrial pressure leads to lower venous return if there are no compensations.
At a right atrial pressure of zero, what is the expected venous return?
About 5 L/min
This is the normal venous return to the heart under healthy conditions.
What is the relationship between cardiac output and venous return?
You can’t have cardiac output without venous return
Cardiac output is directly dependent on the amount of blood returning to the heart.
How does lower right atrial pressure affect venous return?
It increases venous return
A lower right atrial pressure results in a larger delta P, facilitating blood return.
What is the plateau phase in the context of venous return?
Venous return can max out at about 6 L/min
This occurs when right atrial pressure is significantly low, causing large veins to collapse.
What is the mean systemic filling pressure (PSF) at rest?
7 mmHg
This is the average pressure in the cardiovascular system when the heart is paused.
-extra info from textbook : think defibrillation stopping the heart completely this is when we would see this ideal pressure.
What happens to the delta P when the right atrial pressure is 0 mmHg and PSF is 7 mmHg?
Delta P is 7 mmHg
This pressure difference is crucial for filling the right side of the heart.
What typically causes increased systemic filling pressure?
Elevations in resistance
Tightening of systemic veins primarily increases systemic filling pressure.
How does resistance to venous return affect blood flow to the heart?
Lower resistance increases venous return
Easier blood return leads to increased cardiac output.
What occurs to the venous return curve when mean systemic filling pressure is increased?
The curve shifts to the right
This indicates higher venous return without changing the slope.
What is the effect of a higher right atrial pressure on venous return?
Lower venous return
Higher pressures impede blood flow back to the heart.
What is the expected venous return if the filling pressure is increased to 14 mmHg?
About 10 L/min
Doubling the filling pressure can double the venous return, assuming the heart can pump it out.
What is the impact of a reduced systemic filling pressure on venous return?
It decreases venous return
A lower filling pressure reduces the pressure available to return blood to the heart.
True or False: The systemic veins collapsing can augment venous return.
False
Vein collapse limits further augmentation of venous return.
What is the expected relationship between central venous pressure (CVP) and right atrial pressure?
CVP is expected to be in line with right atrial pressure. Increases in right atrial pressure usually generate increases in CVP and vice versa.
What are the two main factors that affect systemic filling pressure?
- Blood Volume
- Venous Tone
How does venous tone influence CVP?
Small changes in the tightness of venous walls can significantly influence CVP and systemic filling pressure.
What happens to veins when facing elevated intra-thoracic pressures?
Veins can collapse, making it difficult for blood to return to the heart.
How does thoracic pressure affect venous return?
Increased thoracic pressure can skew the venous return curve low, making it harder for blood to return to the heart.
What is the expected cardiac output with a right atrial pressure of zero in a healthy heart?
A cardiac output of five liters per minute.
What happens to cardiac output as right atrial pressure increases in a healthy heart?
Cardiac output increases significantly until it reaches a plateau at about 13 liters per minute when right atrial pressure is around four mmHg.
What is the Frank-Starling mechanism?
It explains how better cross-bridge alignment of ventricular muscle fibers leads to more effective contraction and increased stroke volume.
What is direct atrial stretch and its effect on heart rate?
Direct atrial stretch can increase heart rate by about 10 to 15% of normal due to increased filling pressure.
What is the Bainbridge reflex?
A reflex that increases heart rate by about 40 to 50% in response to increased atrial stretch.
What are the two mechanisms through which Bainbridge reflex increases heart rate?
- Increases sympathetic output
- Decreases parasympathetic output
What effect does strong sympathetic stimulation have on cardiac output?
It can increase maximum cardiac output significantly, potentially up to 40 L/min for elite athletes.
How does a hyper-effective heart influence right atrial pressure?
It can lower right atrial pressure, potentially creating a vacuum effect that aids in higher cardiac output.
What happens to right atrial pressure in a heart that is not pumping effectively?
Right atrial pressure is likely to increase due to decreased output.
What does a cardiac output curve look like in congestive heart failure?
It shows that high filling pressures are required to achieve normal cardiac output, as the heart struggles to pump effectively.
What does increasing Central Venous Pressure (CVP) do in patients?
It pushes enough blood into the heart to keep the patient alive
High CVPs in heart failure indicate the heart’s inability to pump effectively, requiring elevated filling pressures.
What are the two main components that determine actual cardiac output?
- Conditions of the circulatory system
- Conditions of the heart
If both parts of the circulatory system are normal, what should the right atrial pressure and both cardiac output and venous return be?
Right atrial pressure should be zero, and both cardiac output and venous return should be five
True or False: Stimulating the heart strongly while keeping the circulatory system unchanged will significantly increase cardiac output.
False
What happens to the venous return curve if filling pressure is increased from 7 to 20?
The venous return curve shifts to the right, indicating a larger return
This change can lead to a higher expected cardiac output, such as 13 liters per minute.
What is the expected outcome when both the heart is strongly stimulated and filling pressure is increased?
Cardiac output should increase significantly
What is the relationship between cardiac output and venous return?
Cardiac output must equal venous return
Fill in the blank: If you increase filling pressure without changing the heart’s contractile state, cardiac output will _____ .
pick up a lot
What does a normal venous return curve indicate in the context of cardiac output?
It shows the relationship between the return of blood to the heart and the output of the heart
What valve(s) would you expect to open/close at the point indicated by 1 in the figure below?
Why?
A-V valves closure.
This occurs due to ventricular pressure exceeding atrial pressure.
What valve(s) would you expect to open/close at the point indicated by 1 in the figure below?
Why?
A-V valves closure.
This occurs due to ventricular pressure exceeding atrial pressure.
What valve(s) would you expect to open/close at the point indicated by 2 in the figure below?
Why?
Aortic valve opening
This occurs due to ventricular pressure exceeding aortic pressure.
What valve(s) would you expect to open/close at the point indicated by 3 in the figure below?
Why?
Aortic valve closure
This occurs due to aortic pressure exceeding ventricular pressure
What valve(s) would you expect to open/close at the point indicated by 4 in the figure below?
Why?
AV valves opening.
This occurs due to atrial pressure exceeding ventricular pressure.
At what point would one expect all 4 cardiac valves to be closed?
Beginning of Phase II & IV
What is depicted by graph (a) on the figure below?
Aortic Pressure
What is depicted by graph (b) on the figure below?
Left Atrial Pressure
What is depicted by graph (c) on the figure below?
Left Ventricular Pressure
What is depicted by graph (d) on the figure below?
Ventricular Volume
What is depicted by graph (e) on the figure below?
Electrocardiogram
What is depicted by graph (f) on the figure below?
Phonocardiogram
In the graph depicted below, what valves would you expect to be closed during the time boxed in with the pink box?
Mitral/Tricuspid valves
