Lecture 4 - Jan 28 Flashcards
What is a mixed vasodilator?
A mixed vasodilator dilates both arteries and veins in the systemic circulation.
What is an example of a mixed vasodilator?
Sodium nitroprusside (nipride) is a mixed vasodilator and a nitric oxide donor.
What effect does a mixed vasodilator have on systemic filling pressure?
It drops the systemic filling pressure and reduces the resistance to venous return.
What is the primary effect of venous vasodilators like nitroglycerin?
They relax the veins more than the arteries, reducing preload and metabolic demands of the heart.
True or False: Nitroglycerin is always the best medication for heart attacks.
False
What is the primary action of ACE inhibitors?
ACE inhibitors primarily reduce afterload.
What makes hydralazine an arterial vasodilator?
It is almost entirely arterial specific, relaxing arteries, though its mechanism of action is unknown.
What is the role of phenylephrine in the circulatory system?
Phenylephrine is a vasoconstrictor that constricts both veins and arteries.
What is the effect of increased preload due to phenylephrine?
It helps the heart pump and increases blood pressure.
What happens to cardiac output after a myocardial infarction (MI)?
Cardiac output decreases, moving from a normal state to a lower output state.
What compensatory mechanisms occur after an MI?
Increased venous tone and stronger heart contractions due to sympathetic nervous system activation.
What is preload?
Preload is the pressure available to fill the heart with blood.
What is afterload?
Afterload is the pressure the heart must pump against, typically the blood pressure outside the aortic valve.
What defines contractility in the heart?
Contractility is the difference in stroke volume while maintaining constant preload and afterload.
Fill in the blank: The body compensates for cardiac failure by _______ venous compliance.
reducing
Fill in the blank: Increased systemic vascular resistance (SVR) makes it _______ to return blood to the heart.
more difficult
What happens to right atrial pressure during cardiac failure?
It increases due to high filling pressures and the heart’s struggle to pump efficiently.
What is the significance of catecholamines in heart function after an MI?
They help maintain heart function but can predispose to arrhythmias if activity is too high.
What occurs as the body retains more fluid after an MI?
Sympathetic activity decreases as blood volume expands.
True or False: High sympathetic activity is ideal for long-term heart function.
False
What is the expected right atrial pressure in a patient dependent on volume?
It is expected to be higher than normal, often around 8 mmHg.
What is afterload?
The force that the heart has to pump against, equivalent to the pressure in the aorta before the aortic valve opens.
Afterload is influenced by systemic vascular resistance and can affect stroke volume.
How does an increase in afterload affect the heart?
It makes it harder for the heart to pump blood, requiring more pressure to open the aortic valve and potentially reducing stroke volume.
Increased afterload can lead to longer duration in the isovolumetric contraction phase.
Define contractility.
A measure of the heart’s ability to contract and is reflected in the change in stroke volume when preload and afterload are held constant.
Increased contractility leads to a greater stroke volume and lower end systolic volume.
What happens to stroke volume if contractility increases while preload and afterload remain constant?
Stroke volume increases because the heart ejects more blood due to stronger contractions.
End systolic volume decreases as a result.
What is preload?
The volume of blood in the ventricle at the end of diastole, which is influenced by the pressure available for filling the heart.
A normal end diastolic volume is approximately 120 mL.
How does increased preload affect filling of the heart?
Increased preload results in more filling and a higher end diastolic volume.
This is due to greater pressure applied to fill the ventricle.
What is the normal stroke volume during systole?
Approximately 70 mL.
Stroke volume is the difference between end diastolic volume and end systolic volume.
True or False: Afterload is primarily determined by preload.
False.
Afterload is determined by the pressure the heart must generate to eject blood, not by preload.
What happens to stroke volume if preload decreases?
Stroke volume decreases due to reduced filling in the ventricle at the end of diastole.
This results in a lower end diastolic volume.
What is the pressure in the aorta before the aortic valve opens during normal conditions?
Approximately 80 mmHg, which represents normal diastolic blood pressure.
This pressure must be overcome for the heart to eject blood.
What are the effects of increased afterload on the cardiac cycle?
It prolongs Phase 2 (isovolumetric contraction) and potentially reduces the time available for ejection during Phase 3.
This can result in a lower stroke volume.
Fill in the blank: The pressure at which the aortic valve closes is influenced by _______.
[afterload].
How does reducing afterload affect stroke volume?
It typically increases stroke volume by allowing the heart to eject blood more efficiently.
This occurs due to lower pressures in the aorta and longer ejection time.
What does a steeper slope in the pressure-volume loop indicate?
Higher contractility, meaning the heart can eject more blood with each contraction.
The position of the curve reflects the heart’s efficiency in pumping.
What happens to end systolic volume when contractility decreases?
End systolic volume increases due to less blood being ejected from the heart.
This is because more blood remains in the ventricle after contraction.
What is the relationship between heart rate and stroke volume when contractility changes?
If heart rate remains unchanged, a decrease in contractility will reduce cardiac output due to lower stroke volume.
Cardiac output is calculated as heart rate multiplied by stroke volume.
What effect does an increased preload have on blood pressure?
It is likely to increase systolic blood pressure due to enhanced stroke volume.
This is a result of the Frank-Starling mechanism.
In the context of the cardiac cycle, what does Phase 2 represent?
The isovolumetric contraction phase where the heart builds pressure to open the aortic valve.
This phase is affected by changes in afterload.
What happens to stroke volume if contractility is reduced?
Stroke volume is reduced, leading to an increase in end systolic volume.
This is because less blood is ejected from the heart.
How does unchanged heart rate affect cardiac output with reduced contractility?
Cardiac output decreases.
This is due to the reduction in the amount of blood pumped with each heartbeat.
What is the relationship between contractility and blood pressure?
Increased contractility likely increases blood pressure; decreased contractility likely decreases blood pressure.
What is a consequence of depressed contractility in a heart with a history of MI?
Higher end systolic volume compared to normal.
This indicates the heart is struggling to pump out a normal stroke volume.
How can treating a weak heart with an afterload reducer help?
It allows greater stroke volume while reducing energy requirements of the heart.
What is passive filling in relation to heart function?
Passive filling refers to the pressure available to fill the heart without active contraction.
What happens to preload in a patient recovering from heart damage?
Preload may increase due to volume retention and blood expansion.
What are the long-term effects of increased preload on the heart?
It can lead to dilation of heart walls and become harmful over time.
What is aortic stenosis?
A condition where the aortic valve becomes narrowed, causing high resistance to blood flow.
What is the effect of aortic stenosis on stroke volume?
It reduces stroke volume, requiring an elevated heart rate to maintain normal cardiac output.
How does a high resistance valve affect pressures in the heart?
High pressures are seen in the ventricle, while lower pressures are found downstream in the aorta.
What happens to pulse pressure in aortic stenosis?
Pulse pressure narrows, typically dropping from 40 to about 20.
What compensatory mechanisms occur with mitral valve stenosis?
Increased preload, systemic filling pressure, and atrial pressure.
What is the primary issue with a stenotic mitral valve?
It leads to reduced filling and lower end diastolic volume.
What defines an insufficient or regurgitant aortic valve?
It allows backward blood flow when the valve is closed.
What happens to end diastolic volume with a leaky aortic valve?
End diastolic volume increases due to filling from both the atria and the aorta.
How does aortic regurgitation affect the pressure-volume loop?
It results in a higher end diastolic volume compared to normal.
What happens to the heart walls over time with severe aortic regurgitation?
The walls can become stretched and thin, leading to worse valve function.
What happens to the end diastolic volume as the problem with valve insufficiency worsens?
It increases as the ventricle gets stretched out
Increased end diastolic volume may lead to thinner ventricular walls and worse valve function.
What is the consequence of the mitral valve being leaky?
Blood moves from the ventricle back into the atria
This occurs when the pressure in the ventricle is higher than in the atria.
Describe the shape of the pressure-volume loop in phase four of a healthy heart.
It is isovolumetric and straight
In a healthy heart, phase four should show no change in volume.
What indicates an increase in backward blood flow during phase four?
A decrease in pressure in the ventricle while pressure in the aorta remains high
This creates a pressure gradient that allows backward flow.
During which phase does the mitral valve remain closed while the ventricle fills?
Phase four
This phase is characterized by increasing ventricular volume due to backward blood flow.
What happens to the pressure gradient as the ventricle fills?
The gradient decreases, resulting in less backward blood flow
As the ventricle fills, the pressure in the ventricle rises, reducing the backward flow.
What occurs when the mitral valve opens during diastole?
The ventricle fills from both the atria and the aorta
This occurs after the first third of diastole, leading to rapid filling.
Fill in the blank: Aortic valve insufficiency is characterized by a ______ pulse pressure.
wide
This is due to low diastolic pressure from backward blood flow.
What is the consequence of a leaky aortic valve?
Blood leaks from the aorta into the ventricle
This occurs when the aortic valve fails to close properly.
What happens to stroke volume in the presence of a leaky aortic valve?
It needs to be larger to compensate for backward flow
This is necessary to maintain adequate forward blood flow despite leakage.
What is the pressure relationship during phase two of mitral regurgitation?
Ventricular pressure is higher than atrial pressure
This pressure difference causes backward flow into the atria.
True or False: In aortic regurgitation, the pressure in the aorta remains high when the aortic valve opens.
False
The pressure in the aorta is low due to backward blood flow.
What shape does the pressure-volume loop of mitral regurgitation resemble?
An ‘M’ shape
This reflects the backward flow of blood into the atria during the cardiac cycle.
What happens during the isovolumetric phase in the presence of leaky valves?
It is no longer truly isovolumetric
Blood may flow inappropriately during this phase due to valve insufficiency.
