EXAM 1: Lecture 3 Flashcards
What are the two main components that determine cardiac output?
The health of the heart and the health of the system.
How does the body enhance cardiac output during exercise?
By changing the systemic filling pressure through constriction of arteries and veins.
What happens to veins during exercise and how does it affect blood return to the heart?
Veins constrict, increasing systemic filling pressure and augmenting blood return to the heart.
What is the primary pressure concern in the thorax related to cardiac output?
Positive pressure ventilation, which can collapse chest veins leading back to the right heart.
What is phenylephrine used for in the context of cardiac output?
To tighten up the veins by working on alpha1 receptors.
What is the normal maximum cardiac output the heart can achieve without other systems involved?
About 13L/min.
How does anesthesia affect systemic filling pressure?
It reduces systemic filling pressure by relaxing blood vessels.
What is the relationship between metabolism and cardiac output?
Cardiac output is heavily dependent on tissue metabolism and increases with metabolic rate.
What happens to cardiac output with increased oxygen consumption?
There is an equally matched increase in cardiac output.
What is cardiac index?
A measure of cardiac output adjusted for body surface area.
How is cardiac index calculated?
Cardiac index = cardiac output (SV x HR) / surface area of the body.
What is the typical cardiac index for a healthy adult?
Approximately 3 L/min/m².
How does aging affect cardiac index?
Cardiac index decreases as muscle mass and organ function decline with age.
What factors can lower metabolic needs and subsequently cardiac output?
Hypothyroidism and removal of limbs.
What factors can increase metabolic needs and subsequently cardiac output?
Hyperthyroidism, beriberi, and an AV shunt.
How do the cardiac outputs of the right and left ventricles compare?
Both are evenly matched at 5L/min but operate under different atrial filling pressures.
What is the relationship between central venous pressure (CVP) and right atrial pressure?
CVP and right atrial pressure go hand in hand; increases in CVP lead to increases in right atrial pressure.
What happens to cardiac output in a very sick heart, such as in congestive heart failure?
The heart may fail to achieve the necessary 5L/min cardiac output.
What is the mean circulatory filling pressure (MCFP)?
Essentially the same as the mean systemic filling pressure, around 7mmHg.
How does sympathetic stimulation affect filling pressure?
Strong sympathetic stimulation increases filling pressure.
What happens to resistance to venous return with an AV fistula?
Resistance decreases, leading to higher cardiac output.
What impact does progressive hemorrhagic shock have on cardiac function?
It decreases blood volume and pressure, weakening the heart over time.
What is intrapleural pressure?
The pressure in the thorax, typically around -4mmHg.
What occurs during inspiration regarding thoracic pressure?
Intrapleural pressure becomes more negative, helping to suck air into the lungs and blood into the heart.
What happens to cardiac output with sustained positive thoracic pressure?
Cardiac output decreases due to impaired filling of the heart.
What happens to cardiac output when there is sustained positive pressure around the heart?
Cardiac output decreases significantly due to difficulty in heart filling
This can occur with positive pressure mechanical ventilation or if the chest cavity is opened to outside air.
What compensatory mechanism occurs when cardiac output decreases after opening the chest cavity?
Increase in right atrial filling pressure
This compensation can help return cardiac output to normal levels.
How does inspiration affect cardiac output?
Inspiration increases cardiac output and shifts the curve to the left
What effect does exhalation have on cardiac output?
Exhalation decreases cardiac output and shifts the curve to the right
What condition can cause extra fluid around the heart, impacting cardiac output?
Cardiac tamponade or pericardial effusion
These conditions inhibit heart filling and decrease venous return.
What is a hypoeffective heart?
A heart that is not functioning properly, resulting in a dampened slope and lower plateau phase on the cardiac output curve
What effect does decreased intrapleural pressure have on the cardiac output graph?
It shifts the graph to the left
What characterizes a hypereffective heart?
A heart that is functioning well, leading to an increased slope and higher plateau phase on the cardiac output curve
What happens when there is increased intrapleural pressure?
It shifts the cardiac output curve to the right
What is the result of enhanced pumping ability on the cardiac output curve?
The curve shifts to the left with an increased plateau, indicating increased cardiac output
What effect do arterial specific vasodilators have on the cardiac output curve?
They decrease resistance to venous return, increasing cardiac output and steepening the slope
What is the role of systemic vascular resistance (SVR) in cardiac output?
SVR affects the resistance to venous return, influencing cardiac output levels
What happens to cardiac output when venous specific vasodilators like nitroglycerin are used?
Cardiac output is reduced due to decreased mean systemic filling pressure
Fill in the blank: A mixed vasodilator will cause both _______ and _______ to occur.
arteriole dilation and venodilation
What occurs when the compliance of the venous system decreases?
Increased filling pressure, leading to increased cardiac output
How does heart failure alter the body’s compensatory mechanisms?
The body constricts veins and increases blood volume to maintain cardiac output
What are the immediate changes in the cardiac output curve after a myocardial infarction (MI)?
A decrease in slope, a decrease in cardiac output to 2L/min, and an increase in right atrial pressure to 4mmHg
What happens during the B-C phase after an MI?
Nervous system increases venous tone and cardiac output returns to almost normal levels
What is the effect of sympathetic stimulation during the C-D phase post-MI?
Cardiac output remains the same while right atrial pressure increases
Fill in the blank: The kidneys help to _______ blood volume in patients with heart failure.
expand
What drug can be used as a mixed vasoconstrictor affecting both arterioles and veins?
Phenylephrine
What is the effect of short term compensation on sympathetic stimulation?
It has the most increase in sympathetic stimulation
Short term compensation increases systemic filling pressure.
What happens to cardiac output and right atrial pressure in the C-D stage?
Cardiac output stays the same at 5L/min, right atrial pressure increases to 6mmHg
Sympathetic activity dials back as fluid is retained and blood volume expands.
In the C-D stage, what causes the decrease in circulating catecholamines?
Increased blood volume retention
Initially, catecholamines cause venous return, but the kidneys retain fluid leading to decreased catecholamines.
What is the right atrial pressure in the D-E stage?
Increases to 8mmHg
There is sustained cardiac output at 5L/min and an increase in systemic filling pressure.
Why is it important to return to normal sympathetic activity?
To reduce the risk of arrhythmias
Sustained sympathetic activity can be harmful to the heart.
What happens to patients who are volume dependent when fluid is removed?
Their heart won’t be able to pump what it needs to
Volume dependency arises from their heart adapting to higher than normal right atrial pressure.
What is the effect of arteriole dilation on cardiac output?
Increases cardiac output
It also increases the slope of the curve and slightly increases right atrial pressure.
What happens to systemic filling pressure during arteriole constriction?
Stays the same
Cardiac output is reduced, and SVR is increased.
What is the effect of venous dilation on cardiac output?
Reduces cardiac output
It also reduces systemic filling pressure with no effect on SVR.
What is the effect of venous constriction on systemic filling pressure?
Increases systemic filling pressure
It increases cardiac output with no effect on SVR.
What does mixed vasodilation do to systemic filling pressure?
Reduces systemic filling pressure
It also reduces cardiac output and SVR.
What happens when volume is added to the system?
Increases systemic filling pressure and cardiac output
It has no effect on the slope.
Fill in the blank: Decreasing or removing volume in the system will _______.
Decrease systemic filling pressure and cardiac output
This also has no effect on the slope.
