Lecture 3 - Jan 23 Flashcards
What are the two components that determine cardiac output?
Health of the heart and health of the system
What is the normal right atrial pressure under healthy conditions?
Zero
What does delta p represent in the context of venous return?
The difference between systemic pressure and right atrial pressure
What is indicated by a low resistance to venous return?
An easy pathway for blood to return to the heart
What happens to venous return if right atrial pressure increases?
Venous return decreases
What is the effect of a hyper effective heart on right atrial pressure?
It decreases right atrial pressure
How does an increase in systemic filling pressure affect venous return?
It increases venous return
Fill in the blank: The systemic filling pressure is defined by the point at which the venous return curve runs into the _______.
X-axis
What effect does positive pressure ventilation have on venous return?
Decreases venous return
What is phenylephrine used for in the venous system?
To tighten up the veins
What is the maximum cardiac output under normal conditions?
13 L/min
What can sympathetic stimulation do to cardiac output?
Increase it significantly
True or False: Removing sympathetic stimulation has a significant effect on cardiac output in a healthy heart.
False
What happens to cardiac output during maximum parasympathetic stimulation?
It reduces cardiac output
What is the impact of a myocardial infarction (MI) on cardiac output?
Reduces cardiac output significantly
How does a hypo-effective heart affect right atrial pressure?
It increases right atrial pressure
What typically happens to the right atrial pressure in heart failure?
It increases
What compensatory mechanism does the body use to address heart problems?
Increases filling pressures
What is the relationship between systemic filling pressure and cardiac output?
Higher systemic filling pressure increases cardiac output
What occurs when the circulatory system compensates for heart problems?
It increases systemic filling pressure to enhance cardiac output
Fill in the blank: The right atrial pressure is often elevated in patients with _______.
Heart problems
What happens to the venous return curve when systemic filling pressure is increased?
Shifts to the right
What does a weak heart imply for cardiac output and right atrial pressure?
Lower cardiac output and higher right atrial pressure
What happens to right atrial pressure without compensation?
It is only 3
This indicates a normal physiological state without compensatory mechanisms in place.
What is the expected right atrial pressure with compensation?
Sky high – probably 12-13
This suggests a significant increase in filling pressure due to compensatory mechanisms.
What role do catecholamines play in cardiac output compensation?
They tighten the system and increase water retention by the kidneys
Catecholamines like epinephrine and norepinephrine are critical in short-term cardiovascular responses.
What happens to catecholamine levels in long-term heart issues?
They typically go down, and blood volume increases
This reflects a shift from acute to chronic compensatory mechanisms.
How do anesthetics affect systemic filling pressure?
They reduce it by relaxing blood vessels
This can lead to complications in patients with high right atrial pressure.
What is the relationship between venous return curve and cardiac output?
The intersection indicates normal conditions for a cardiac output of about 13
Cardiac output is capped at 5 under normal conditions with zero right atrial pressure.
What does an increase in filling pressure do to cardiac output?
It can achieve a maximum output of 13 liters per minute
This occurs without changing heart function, emphasizing the importance of venous return.
How does metabolic rate influence cardiac output?
Higher metabolic rates typically increase cardiac output
This is achieved through vasodilation of blood vessels to active tissues.
What effect does hypothyroidism have on cardiac output?
It typically reduces cardiac output due to lower metabolic needs
Thyroid hormone is essential for regulating metabolic rate.
What happens to cardiac output when vascular resistance increases?
Cardiac output is reduced
Increased vascular resistance indicates less blood flow due to tighter blood vessels.
What is the impact of hyperthyroidism on cardiac output?
It increases cardiac output due to higher metabolic demands
This results from decreased vascular resistance.
What does an arteriovenous (AV) shunt do to vascular resistance?
It reduces vascular resistance
This increases cardiac output by providing an additional pathway for blood flow.
How does oxygen consumption relate to cardiac output?
Increases in oxygen consumption are matched by increases in cardiac output
This relationship is crucial for meeting tissue metabolic needs.
What is dinitrophenol’s effect on cardiac output?
It increases cardiac output by driving up tissue metabolism
Its effectiveness depends on the nervous system functioning normally.
What is the cardiac index and how is it calculated?
Cardiac output divided by body surface area
It is measured in L/min/m^2 and reflects individual metabolic needs.
What typically happens to cardiac index as we age?
It decreases due to reduced energy requirements
A healthy 80-year-old’s cardiac index may drop to about 2.4.
What is the difference in filling pressures between the left and right sides of the heart?
Right atrial pressure is 0, left atrial pressure is 2
This reflects the different workloads and resistances faced by each side.
How does central venous pressure (CVP) relate to right atrial pressure?
CVP and right atrial pressure move in tandem
CVP is affected by distance from the heart, impacting pressure readings.
What effect does the sympathetic nervous system have on venous return?
It helps maintain venous tone to support cardiac output
Loss of sympathetic outflow can lead to low filling pressures and inadequate cardiac output.
What is the expected pressure measured right outside the right atrium?
Pretty close to zero
It won’t be zero due to the need for some pressure gradient.
What happens to atrial pressure as individuals age?
Typically increases
This is often a function of increased central venous pressure (CVP).
How does gravitational pressure affect venous pressure in a supine patient?
It can increase the pressure measured
The inferior vena cava is typically at a lower altitude than the heart in a supine position.
What is the relationship between cardiac output and filling pressure?
Increased filling pressure can help compensate for low cardiac output
This may involve interventions like a ventricular assist device or medication.
What is the mean circulatory filling pressure?
Approximately the same as the mean systemic filling pressure, about 7 mmHg
It reflects pressure throughout both pulmonary and systemic circuits.
What happens to pressure in the circulatory system when volume is increased?
Pressure goes up
Conversely, taking volume away causes pressure to go down.
What effect does strong sympathetic stimulation have on circulatory pressure?
It increases the pressure of the system
A reduction in sympathetic tone leads to lower pressures.
What is the primary obstacle to venous return?
High pressures in the thorax
This can collapse chest veins and hinder blood return to the heart.
What occurs in the heart during progressive hemorrhagic shock?
The heart becomes weaker over time due to inadequate blood volume and pressure
This can lead to a death spiral of heart function if not intervened.
What effect does inspiration have on cardiac output?
Cardiac output increases
This is due to reduced pleural pressure, which helps suck blood into the heart.
What happens when there is sustained positive pressure surrounding the heart?
Cardiac output decreases
This can occur with mechanical ventilation or opening the chest to the atmosphere.
Fill in the blank: If there is extra fluid around the heart, it can cause a _______ in cardiac output.
Decrease
What happens when both pleural pressure and cardiac function curve are altered?
They can shift from right to left
A hypo-effective heart shifts the curve left, while a hyper-effective heart shifts it right.
What is systemic vascular resistance (SVR) primarily governed by?
Resistance at the level of the arterioles
This creates a choke point where arterial pressure is high upstream and low downstream.
True or False: The right atrial pressure should be lower than normal if the heart is pumping strongly.
True
What is a common consequence of having an arteriovenous (AV) fistula?
Increased blood volume
This occurs to compensate for the open pathway between arteries and veins.
What effect does a reduction in pleural pressure have on the cardiac output curve?
Shifts it to the left
This typically results in increased cardiac output.
What happens to cardiac output if the heart is functioning at a depressed capacity?
It shifts the cardiac output curve to the right
Expect to see higher right atrial pressure.
What is the choke point in the vascular system?
The choke point occurs at the level of the arterioles, where vascular resistance is high.
What happens to arterial pressure upstream and downstream of the choke point?
Upstream, arterial pressure is high; downstream, pressure is low.
What does systemic vascular resistance (SVR) primarily govern?
SVR is mainly governed at the arterioles where the choke point is located.
What is the effect of arterial-specific vasodilators on venous return?
They reduce SVR, making it easier to get blood from the left heart to the right heart.
When arterial-specific vasodilators are used, how does pressure change in the system?
Overall pressure in the system does not change much; upstream pressure is reduced, and downstream pressure is elevated.
What is an example of an arterial-specific vasodilator?
ACE inhibitor.
What is the effect of venular-specific vasodilators like nitroglycerin?
They dilate the veins, reducing filling pressure (CVP).
How does venous dilation affect cardiac output?
It reduces filling pressure, leading to a lower cardiac output if the heart’s pumping effectiveness remains unchanged.
What is the primary effect of mixed vasodilators on filling pressure and resistance to venous return?
They decrease filling pressure while reducing resistance to venous return.
In the case of mixed vasodilators, which change is more significant in determining cardiac output?
The reduction in filling pressure outweighs the reduction in resistance to venous return.
How can filling pressure be increased?
By constricting veins or adding volume to the system.
What is venous compliance?
A measure of how stretchy the walls of the veins are.
What happens to filling pressure when venous compliance is reduced?
Filling pressure increases.
What is the impact of arterial constriction on the venous return curve?
It reduces the slope of the venous return curve.
What adjustments does the body make in response to a damaged heart?
Veins tighten to increase filling pressure and SVR may increase to shunt blood away from less vital areas.
What long-term adjustment occurs in response to chronic heart problems?
The kidneys may expand blood volume to improve venous return without continuous vessel constriction.
True or False: Nitroglycerin primarily acts as an afterload reducer.
False; it primarily reduces preload.
