Exam 1: 23 Jan 25 Determinants of CO and BP Flashcards
What are the two main components that determine cardiac output?
Health of the heart and health of the system.
What should the right atrial pressure be under normal operating conditions?
Zero.
What does the delta p represent in the context of venous return?
The difference between the systemic pressure and the right atrial pressure.
What is indicated by a normal resistance to venous return on a graph?
A normal slope of the curve.
How does high resistance to venous return appear on a chart?
Indicated by a curve with a lower than normal slope.
If the right atrial pressure increases, what is expected to happen to venous return?
It will decrease.
What happens to venous return if the right atrial pressure decreases?
It can increase.
What factors can modify the characteristics of the circulatory system?
- Resistance to venous return
- Systemic filling pressure.
What is the effect of increased systemic filling pressure on venous return?
It increases venous return.
What happens to venous return when systemic filling pressure is reduced?
Venous return decreases.
How does the body typically enhance cardiac output during exercise?
By changing the systemic filling pressure.
What role do veins play during exercise in relation to cardiac output?
Veins constrict to increase blood return to the heart.
What is the primary obstacle to venous return during positive pressure ventilation?
Increased pressure in the thorax.
What is the primary effect of phenylephrine on the venous system?
It tightens the veins.
What is the maximum cardiac output achievable without sympathetic stimulation?
About 13 L/min.
What can sympathetic stimulation increase maximum cardiac output to?
About 25 L/min.
What effect does maximum parasympathetic stimulation have on cardiac output?
It reduces cardiac output.
What happens to the cardiac output curve in a patient with a myocardial infarction (MI)?
It shifts downwards, indicating reduced pumping effectiveness.
What happens to right atrial pressure in a hypo-effective heart?
It shifts to the right.
What happens to right atrial pressure in a hyper-effective heart?
It shifts to the left.
What determines the intersection point of the venous return curve and the cardiac output curve?
The actual conditions of the circulatory system.
What is the effect of sympathetic stimulation on cardiac output if the circulatory system remains unchanged?
It increases cardiac output slightly, capped at around 6 L/min.
In the presence of catecholamines affecting the heart, what happens to filling pressures?
They increase, enhancing venous return.
What characterizes a weak heart?
A weak heart is characterized by reduced cardiac output and increased right atrial pressure.
This condition may arise from issues such as myocardial infarction (MI).
What happens to cardiac output in the presence of a weak heart?
Cardiac output decreases.
The right atrial pressure increases as the heart struggles to pump blood effectively.
What is the relationship between central venous pressure (CVP) and heart problems?
CVP is almost always elevated in individuals with heart problems.
This occurs as the heart struggles to pump out returning blood.
What occurs in heart failure regarding right atrial pressure?
Right atrial pressure increases significantly, often up to 3 mmHg or higher.
This is due to the heart’s inability to maintain adequate cardiac output.
How does the body compensate for a failing heart?
The body increases filling pressures to assist the struggling heart.
This may involve increasing venous return to improve cardiac output.
What effect do catecholamines have on the circulatory system?
Catecholamines tighten blood vessels and increase water retention by the kidneys.
This response helps to maintain blood pressure and volume in acute heart issues.
How do anesthetics affect systemic filling pressure?
Anesthetics reduce systemic filling pressure by relaxing blood vessels.
This can lead to a drop in cardiac output in patients reliant on high filling pressures.
What is the significance of the intersection of the venous return curve and cardiac output curve?
The intersection indicates the balance between venous return and cardiac output.
Both sides of the heart must operate similarly to avoid fluid overload or deficiency.
How does metabolic rate influence cardiac output?
Cardiac output increases with higher metabolic rates due to vasodilation in active tissues.
Conversely, lower metabolic rates allow for lower cardiac output.
What happens to cardiac output in hypothyroidism?
Cardiac output decreases due to lower metabolic rates and increased vascular resistance.
Thyroid hormone plays a crucial role in regulating metabolic rates.
What is the effect of hyperthyroidism on cardiac output?
Hyperthyroidism increases metabolic rate, leading to increased cardiac output.
This is due to lower vascular resistance in tissues requiring more blood.
What is BeriBeri, and how does it affect cardiac output?
BeriBeri is a vitamin B1 deficiency that increases the need for energy delivery, thus raising cardiac output.
It results in cells being less efficient in energy utilization.
How do AV shunts affect cardiac output?
AV shunts lower vascular resistance, thus increasing cardiac output.
An extra connection in the circulatory system allows more pathways for blood flow.
What is the relationship between oxygen consumption and cardiac output?
Increases in oxygen consumption typically correlate with increases in cardiac output.
Both parameters adjust to meet metabolic demands.
What happens to cardiac output when dinitrophenol is administered?
Dinitrophenol increases metabolic rate and subsequently cardiac output, provided the nervous system is functioning.
Without sympathetic nervous system support, cardiac output may not increase effectively.
True or False: The body can compensate for heart failure by decreasing blood volume.
False. The body compensates by increasing blood volume to support cardiac output.
Fill in the blank: If the metabolic rate is low, the cardiac output can be _______.
lower.
What happens to blood pressure when the sympathetic nervous system is removed?
Blood pressure crashes
The sympathetic nervous system is crucial for maintaining stable blood pressure.
What is the primary responsibility of the heart regarding cardiac output?
To handle tissue metabolism
The heart cooperates with the circulatory system to maintain adequate cardiac output.
How is cardiac index calculated?
Cardiac output divided by surface area of the body (L/min/m^2)
Typical surface area for a 70 kg adult is 1.7 m².
What factors can affect cardiac index?
- Gender
- Pregnancy
- Age
Cardiac index can vary based on several physiological factors.
At what age does cardiac index typically max out?
Around age 10
Cardiac index increases rapidly from birth to age 10.
What happens to cardiac index as we age?
It decreases
A healthy 80-year-old has a cardiac index of about 2.4.
What is the typical pressure in the right atrium?
0 mmHg
The left atrial pressure is typically around 2 mmHg.
How do central venous pressure (CVP) and right atrial pressure correlate?
They usually move in tandem
CVP is influenced by the distance from the heart where it is measured.
What effect does sympathetic stimulation have on mean circulatory filling pressure?
It increases the pressure
Conversely, a reduction in sympathetic tone decreases the pressure.
What is a common consequence of progressive hemorrhagic shock?
The heart becomes a weaker pump
Insufficient blood volume leads to inadequate perfusion of the heart.
What happens to cardiac output during inspiration?
It typically increases
Negative pressure in the thorax helps suck blood into the heart.
What is the normal intrapleural pressure?
-4 mmHg
This negative pressure aids in respiration and venous return.
Fill in the blank: The cardiac index is typically around ______ for a healthy 20-year-old patient.
3.0
This is based on a normal cardiac output for a 70 kg individual.
True or False: The left side of the heart works harder than the right side.
True
The left side pumps against higher resistance.
What is the relationship between filling pressure and cardiac output?
Higher filling pressure typically leads to higher cardiac output
This is crucial for maintaining blood circulation.
What happens to venous return resistance in cases such as an AV fistula?
Resistance to venous return decreases
This can lead to increased cardiac output despite normal filling pressure.
What is mean circulatory filling pressure approximately equal to?
Mean systemic filling pressure
Both pressures are about 7 mmHg.
What happens to cardiac output if the pressure surrounding the pump is more negative?
Higher output
This is reflected by the cardiac output curve shifting to the left.
What occurs during forceful expiration?
Increased thoracic pressure
This typically involves contraction of the abdomen to push air out quickly.
What is expected if there is a sustained increase in thoracic pressure?
Drop in cardiac output
What happens to cardiac output during normal inspiration?
Cardiac output increases
What effect does a sustained positive pressure surrounding the heart have on cardiac output?
Shifts the curve to the right, leading to lower cardiac output
What is one example that could cause sustained positive pressure around the heart?
Mechanical ventilation
What happens to cardiac output when the chest is opened to the outside environment?
Cardiac output decreases
How can the body compensate for high pressure surrounding the heart?
Increase filling pressure or add volume to the system
What happens if there is fluid surrounding the heart?
May shift the curve to the right and depress the slope of the cardiac output curves
What is the expected outcome if the heart can’t fill adequately due to extra fluid?
Low cardiac output
What is a hypo-effective heart characterized by?
Lower plateau phase of the cardiac output curve
What effect does a hyper-effective heart have on the cardiac output curve?
Increases the plateau phase
What is systemic vascular resistance primarily governed by?
Arterioles
What happens when arterial-specific vasodilators are used?
Easier blood flow from left heart to right heart
What is an example of an arterial-specific vasodilator?
ACE inhibitor
What effect do venular-specific vasodilators have on filling pressure?
Reduce filling pressure
What is an example of a venular-specific vasodilator?
Nitroglycerin
What is a mixed vasodilator expected to change?
Both filling pressure and resistance to venous return
What is the impact of venodilation on filling pressure?
It reduces filling pressure
What happens to cardiac output if filling pressure is low?
Cardiac output will be much lower
What can happen if the heart is stimulated to pump harder while blood return is low?
Not much help
What is the main factor that influences cardiac output when both filling pressure and resistance to venous return change?
Filling pressure
The reduction in filling pressure outweighs the reduction in resistance to venous return.
What happens to cardiac output when filling pressure decreases?
It drops
The net result of decreased filling pressure and reduced resistance to venous return is a drop in cardiac output.
What are the two variables that affect the return of blood to the heart?
Filling pressure and resistance to venous return
Both variables can oppose each other, but filling pressure is more influential.
How can filling pressure be increased?
By constricting veins or adding volume
Both actions increase filling pressure without changing the path blood takes back to the heart.
What does venous compliance measure?
How stretchy the walls of the vein are
High compliance means low pressure; low compliance means higher pressure.
What effect does a reduction in venous compliance have on filling pressure?
It increases filling pressure
Tighter walls of veins lead to higher filling pressure.
What happens to cardiac output if volume is lost or veins dilate?
It decreases
Lower volume or increased venous compliance results in lower expected filling pressure.
What is the relationship between systemic vascular resistance (SVR) and arterial constriction?
Arterial constriction increases SVR
Increased SVR makes it harder for blood to flow from the left heart to the right heart.
True or False: Relaxing the choke point changes the average pressure in the system.
False
Average pressure should remain about the same if nothing else is changing.
What happens to venous compliance during heart problems?
It decreases
This tightening increases filling pressure to help drive cardiac output.
What compensatory mechanism occurs during a heart attack?
Venous and arterial constriction
The body constricts blood vessels to redirect blood where it’s most needed.
What long-term change occurs if a heart problem is persistent?
Expansion of blood volume
The kidneys help to expand blood volume instead of relying on constant constriction.
Fill in the blank: The body typically backs off the squeeze of blood vessels by _______.
filling them up
This reduces the need for constant sympathetic activation.
