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Questions and Answers
According to the principles governing cardiac output, what effect would a chronically elevated total peripheral resistance have on cardiac output, assuming no other compensatory mechanisms?
According to the principles governing cardiac output, what effect would a chronically elevated total peripheral resistance have on cardiac output, assuming no other compensatory mechanisms?
- Cardiac output would initially increase and then return to normal.
- Cardiac output would remain unchanged due to homeostatic reflexes.
- Cardiac output would decrease. (correct)
- Cardiac output would increase.
During strenuous exercise, the skeletal muscles' increased nutritional demands lead to arterial vasodilation, decreasing peripheral vascular resistance. How does the body primarily prevent a drastic drop in blood pressure under these circumstances?
During strenuous exercise, the skeletal muscles' increased nutritional demands lead to arterial vasodilation, decreasing peripheral vascular resistance. How does the body primarily prevent a drastic drop in blood pressure under these circumstances?
- By inhibiting sympathetic nervous system activity.
- By decreasing heart rate and reducing venous return.
- By increasing heart rate and increasing venous tone. (correct)
- By releasing vasodilatory substances that counteract the effect.
A patient is placed on positive pressure ventilation in the ICU. What is the most direct effect of this intervention on cardiac output?
A patient is placed on positive pressure ventilation in the ICU. What is the most direct effect of this intervention on cardiac output?
- Increased left atrial filling.
- Reduced total peripheral resistance.
- Increased sympathetic drive to the heart.
- Decreased venous return due to increased right atrial pressure. (correct)
According to the Frank-Starling mechanism, what is the immediate effect of increased preload on the heart?
According to the Frank-Starling mechanism, what is the immediate effect of increased preload on the heart?
What is the significance of mean systemic filling pressure in the context of venous return?
What is the significance of mean systemic filling pressure in the context of venous return?
According to the relationship between venous return and right atrial pressure, what occurs when right atrial pressure rises to approximately 7 mmHg?
According to the relationship between venous return and right atrial pressure, what occurs when right atrial pressure rises to approximately 7 mmHg?
Below what right atrial pressure does venous return plateau, despite further decreases in pressure?
Below what right atrial pressure does venous return plateau, despite further decreases in pressure?
If a patient's blood volume increases from 4000 ml to 5000 ml due to fluid infusion, how is the mean circulatory filling pressure affected?
If a patient's blood volume increases from 4000 ml to 5000 ml due to fluid infusion, how is the mean circulatory filling pressure affected?
A patient's mean systemic filling pressure is measured to be 3.5 mmHg. What does this suggest about their circulatory status?
A patient's mean systemic filling pressure is measured to be 3.5 mmHg. What does this suggest about their circulatory status?
In the venous return equation, what does the resistance to venous return represent?
In the venous return equation, what does the resistance to venous return represent?
According to the Fick principle, if the blood entering the heart has an oxygen concentration of 160 ml/L and the blood leaving has a concentration of 200 ml/L, and the total quantity of oxygen absorbed per minute is 200 ml, what is the cardiac output?
According to the Fick principle, if the blood entering the heart has an oxygen concentration of 160 ml/L and the blood leaving has a concentration of 200 ml/L, and the total quantity of oxygen absorbed per minute is 200 ml, what is the cardiac output?
In the indicator dilution method for estimating cardiac output, what substance is injected into a large vein?
In the indicator dilution method for estimating cardiac output, what substance is injected into a large vein?
What parameter is directly calculated from the velocity of blood flowing into the aorta when using echocardiography to determine cardiac output?
What parameter is directly calculated from the velocity of blood flowing into the aorta when using echocardiography to determine cardiac output?
How does atrial stretch contribute to increased heart rate?
How does atrial stretch contribute to increased heart rate?
What is the primary determinant of cardiac output, according to the relationship between blood flow and tissue metabolism?
What is the primary determinant of cardiac output, according to the relationship between blood flow and tissue metabolism?
What is the most direct consequence of decreased peripheral vascular resistance?
What is the most direct consequence of decreased peripheral vascular resistance?
In anesthesia and healthcare, why is understanding the relationship between systemic vascular resistance (SVR), flow, preload, and cardiac output essential?
In anesthesia and healthcare, why is understanding the relationship between systemic vascular resistance (SVR), flow, preload, and cardiac output essential?
How does increased right atrial pressure affect venous return to the heart?
How does increased right atrial pressure affect venous return to the heart?
Under what condition does cardiac output exceed twice its normal volume?
Under what condition does cardiac output exceed twice its normal volume?
How does increased venous return affect cardiac output, up to a certain limit?
How does increased venous return affect cardiac output, up to a certain limit?
Flashcards
Cardiac Output
Cardiac Output
The amount of blood pumped by the heart per minute, typically 5.6L for men and 4.9L for women.
Venous Return
Venous Return
The sum of blood flow from all tissues returning to the heart.
Atrial Stretch Effect
Atrial Stretch Effect
Increased preload leads to increased stretch, resulting in increased heart rate.
Ohm's Law in Circulation
Ohm's Law in Circulation
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Starling's Law
Starling's Law
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Hyper Effective Heart
Hyper Effective Heart
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Compensatory Response to Decreased SVR
Compensatory Response to Decreased SVR
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Effect of Positive Pressure on Heart
Effect of Positive Pressure on Heart
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Venous Collapse
Venous Collapse
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Sympathetic Stimulation Effect
Sympathetic Stimulation Effect
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Venous Return Formula
Venous Return Formula
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Fick Principle
Fick Principle
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Indicator Dilution Method
Indicator Dilution Method
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Echocardiogram for Cardiac Output
Echocardiogram for Cardiac Output
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Study Notes
- Cardiac output (CO) averages 5 liters per minute, specifically 5.6 L/min in men and 4.9 L/min in women.
- Factors influencing cardiac output include metabolism level, activity level, age, and body size.
- Increased preload leads to increased stretch, subsequently raising the heart rate: as per the Frank-Starling mechanism.
- Atrial stretch can elevate sinoatrial node activity by 10-15%.
Venous Return and Cardiac Output
- Venous return is the total blood flow from all local tissues.
- Blood flow in each tissue is directly related to its metabolism and oxygen consumption.
- Cardiac output is primarily determined by local tissue metabolism needs.
- Cardiac output varies inversely with total peripheral resistance (TPR): Ohm's Law (Flow = ΔP/R).
- Long-term changes in resistance cause opposite changes in cardiac output.
- The heart pumps the blood returned to it, up to a limit (Starling's Law).
- Sympathetic stimulation increases heart rate and contractility, potentially doubling cardiac output.
- Hypertrophy increases heart muscle mass and contractile strength, similar to the effects of exercise.
- Hypereffective heart is generally caused by any factor that reduces the heart's pumping ability.
Peripheral Resistance and Blood Pressure
- Decreased peripheral vascular resistance without adequate sympathetic input leads to decreased cardiac output and blood pressure.
- During exercise, skeletal muscle needs cause arterial relaxation, reducing peripheral vascular resistance.
- The nervous system quickly increases heart rate and venous tone to maintain blood pressure during decreased resistance.
- Understanding the relationships between systemic vascular resistance (SVR), flow, preload, and cardiac output is crucial in anesthesia and healthcare.
- Regional anesthesia can lower SVR without sympathetic stimulation.
External Pressure and Venous Return
- External pressure on the heart can decrease right atrial filling, reducing cardiac output.
- Positive pressure ventilation increases right atrial pressure, hindering venous return.
- Increased right atrial pressure acts as a barrier to venous return.
- Venous return decreases to zero when right atrial pressure rises to 7 mmHg.
- Short-term venous return increases with decreasing atrial pressure until a plateau at approximately -2 mmHg; further decreases don't increase venous return due to vein collapse.
Blood Volume and Pressure
- With a blood volume of about 4000ml, the main systemic filling pressure is roughly zero.
- Increasing blood volume to 5000ml raises the mean circulatory filling pressure to 7 mmHg.
- Intense sympathetic stimulation constricts blood vessels, increasing mean systemic filling pressure and venous return.
- Normal mean systemic filling pressure is about 7 mmHg, but can range from 3.5 to 14 mmHg.
- At mean systemic filling pressure and right atrial pressure of 7 mmHg, venous return is about 6 liters/minute.
- Increased mean systemic filling pressure shifts the venous return curve to the right.
- As right atrial pressure rises, mean systemic filling pressure decreases until they are equal, stopping blood flow to the right atrium.
- Venous return is calculated as (Mean Systemic Filling Pressure - Right Atrial Pressure) / Resistance to Venous Return (a modified Ohm's Law).
Estimating Cardiac Output
- Clinical devices estimating cardiac output are compared against the Fick principle or the indicator dilution method.
Fick Principle
- The Fick principle estimates cardiac output via the amount of dissolved O2 in the blood.
- Blood entering the heart has an oxygen concentration of 160 mL/L, and blood leaving has 200 mL/L.
- The blood absorbs 40 mL of oxygen per pass through the lungs.
- If the total oxygen absorbed per minute is 200 mL, then 200/40 = 5 liters of blood pass through the lungs each minute.
Indicator Dilution Method
- The indicator dilution method uses dye injected into a large vein (e.g., right atrium) to measure blood flow.
- Dye concentration is measured in a peripheral artery over time for analysis.
- Time for flow is measured for cardiac output estimation.
Echocardiogram
- Echocardiograms calculate stroke volume from the velocity of blood flowing into the aorta.
- Cardiac output can be easily calculated from stroke volume.
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