Balance Wk 3 LG3 Cardiovascular Balance: Coupling of Cardiac and Vascular Function

What two curves make up a Guyton plot?

Answer: The cardiac function (Starling) curve and the vascular function (venous return) curve.

Extra Information:

• Their intersection defines the cardiovascular equilibrium point.

What does the intersection of the cardiac function and venous return curves represent?

Answer: The equilibrium where cardiac output equals venous return.

Extra Information:

• This intersection is the operating point of the cardiovascular system.

What is on the x-axis of the standard Guyton plot?

Answer: Right atrial pressure.

Extra Information:

• The lecture expresses right atrial pressure in mmHg.

What is on the y-axis of the standard Guyton plot?

Answer: Cardiac output or venous return.

Extra Information:

• The lecture expresses flow in L/min.

How does the cardiac function curve relate right atrial pressure to cardiac output?

Answer: As right atrial pressure or preload rises, cardiac output rises along the Starling curve until it plateaus.

Extra Information:

• The curve reflects Frank-Starling behavior.

How does the venous return curve relate right atrial pressure to venous return?

Answer: Venous return falls as right atrial pressure rises.

Extra Information:

• The vascular function curve therefore slopes downward on the Guyton plot.

What does the x-intercept of the venous return curve represent?

Answer: Mean systemic pressure or mean systemic filling pressure.

Extra Information:

• At this pressure, venous return is zero.

What happens to systemic arterial and venous pressures during cardiac arrest at steady state?

Answer: They equalize at about 7 mmHg.

Extra Information:

• The slide shows zero flow when arterial and venous pressures are equal.

What are the control-state values shown for flow, venous pressure, and arterial pressure?

Answer: Flow is 5 L/min, venous pressure is 2 mmHg, and arterial pressure is 102 mmHg.

Extra Information:

• These values are used to illustrate peripheral resistance.

What peripheral resistance is calculated from the control-state example?

Answer: 20 mmHg/L/min.

Extra Information:

• The slide calculates resistance as (102 − 2) ÷ 5.

How does increased contractility affect the Starling curve?

Answer: It shifts the cardiac function curve upward.

Extra Information:

• At the same preload, cardiac output is higher.

How does decreased contractility affect the Starling curve?

Answer: It shifts the cardiac function curve downward.

Extra Information:

• At the same preload, cardiac output is lower.

What does the failing-ventricle portion of the Starling diagram show at high preload?

Answer: Cardiac output can fall despite further increases in preload.

Extra Information:

• The lecture depicts a descending failing-ventricle portion of the curve.

What is preload?

Answer: The amount of blood in the ventricle at the end of diastole, ready to be pumped out.

Extra Information:

• The lecture's memory cue is "prepare to pump."

What is afterload?

Answer: The resistance the heart must work against to pump blood out of the ventricles during systole.

Extra Information:

• The lecture's memory cue is "against the pressure."

On a left ventricular pressure-volume loop, what event occurs when the mitral valve closes?

Answer: End-diastole is reached and isovolumetric contraction begins.

Extra Information:

• This is point B on the lecture's standard pressure-volume loop.

On a left ventricular pressure-volume loop, what event occurs when the aortic valve opens?

Answer: Ventricular ejection begins.

Extra Information:

• This is point C on the lecture's standard pressure-volume loop.

On a left ventricular pressure-volume loop, what event occurs when the aortic valve closes?

Answer: Ejection ends and isovolumetric relaxation begins.

Extra Information:

• This is point D on the lecture's standard pressure-volume loop.

On a left ventricular pressure-volume loop, what event occurs when the mitral valve opens?

Answer: Ventricular filling begins.

Extra Information:

• This is point A on the lecture's standard pressure-volume loop.

What does the horizontal width of a pressure-volume loop represent?

Answer: Stroke volume.

Extra Information:

• It reflects the difference between end-diastolic volume and end-systolic volume.

How does increased preload change the pressure-volume loop?

Answer: It increases end-diastolic volume and widens the loop.

Extra Information:

• The lecture's figure shows a rightward expansion with increased preload.

How does decreased preload change the pressure-volume loop?

Answer: It decreases end-diastolic volume and narrows the loop.

Extra Information:

• The lecture depicts a smaller loop with decreased preload.

How does increased afterload change the pressure-volume loop?

Answer: It raises ventricular systolic pressure and increases end-systolic volume.

Extra Information:

• The lecture depicts a taller loop with less effective ventricular emptying.

How does decreased afterload change the pressure-volume loop?

Answer: It lowers ventricular systolic pressure and allows greater ventricular emptying.

Extra Information:

• This is contrasted with the increased-afterload loop.

How does the right ventricular pressure-volume loop differ from the left ventricular loop in the lecture diagram?

Answer: It has lower systolic pressure and lower effective afterload.

Extra Information:

• The diagram also labels a lower end-systolic pressure-volume relationship slope.
• A larger end-diastolic volume is shown.

What happens to the venous return curve when blood volume increases?

Answer: It shifts up and to the right.

Extra Information:

• The cardiac function curve remains unchanged if cardiac function itself has not changed.

What happens to the Guyton equilibrium point when blood volume increases?

Answer: Cardiac output and right atrial pressure both increase.

Extra Information:

• The new intersection moves up and to the right.

What happens to the venous return curve when blood volume decreases?

Answer: It shifts down and to the left.

Extra Information:

• This reflects reduced circulating volume.

What happens to the Guyton equilibrium point when blood volume decreases?

Answer: Cardiac output and right atrial pressure both decrease.

Extra Information:

• The new intersection moves down and to the left.

In the lecture's hypovolemia example, what are the before and after values?

Answer: Before: CO 5.1 L/min and RAP 1.9 mmHg. After: CO 4.3 L/min and RAP 0.2 mmHg.

Extra Information:

• Both cardiac output and right atrial pressure fall.

What acute scenario produces the lecture's hypovolemia Guyton shift?

Answer: A trauma patient loses roughly 1 L of blood over a few minutes before compensation occurs.

Extra Information:

• The example specifically states that compensation has not yet kicked in.

In the lecture's hypervolemia example, what are the before and after values?

Answer: Before: CO 5.1 L/min and RAP 1.9 mmHg. After: CO 5.8 L/min and RAP 4.2 mmHg.

Extra Information:

• Both cardiac output and right atrial pressure increase.

What scenario produces the lecture's hypervolemia Guyton shift?

Answer: Several days of very high sodium intake cause the kidney to retain fluid and plasma volume to increase.

Extra Information:

• This links renal volume regulation to cardiovascular function.

How does high sodium intake alter cardiac output in the lecture example?

Answer: Increased plasma volume shifts venous return up and right and increases cardiac output.

Extra Information:

• Right atrial pressure also increases.

What are the four listed hemodynamic features of aortic stenosis?

Answer: High outflow resistance, a large pressure gradient, decreased stroke volume, and increased end-systolic volume.

Extra Information:

• These are the lecture's stated pressure-volume consequences.

Why does aortic stenosis reduce stroke volume according to the lecture?

Answer: The stenotic valve creates high outflow resistance and a large pressure gradient.

Extra Information:

• The ventricle empties less effectively.
• End-systolic volume increases.

How does aortic stenosis change end-systolic volume?

Answer: It increases end-systolic volume.

Extra Information:

• The lecture pairs this with decreased stroke volume.

How does aortic stenosis alter the pressure-volume loop?

Answer: It produces a higher-pressure loop with reduced stroke volume and increased end-systolic volume.

Extra Information:

• The lesion increases resistance to ventricular outflow.

What is the defining flow abnormality in aortic regurgitation?

Answer: Blood flows backward during diastole.

Extra Information:

• The abnormal flow occurs through the aortic valve.

Why is there no true isovolumetric relaxation in aortic regurgitation?

Answer: Blood flows back into the ventricle during diastole, so ventricular volume is not constant during relaxation.

Extra Information:

• The lecture explicitly states that isovolumetric relaxation is disrupted.

What hemodynamic features does the lecture list for aortic regurgitation?

Answer: Diastolic backflow, no true isovolumetric relaxation, a large pressure gradient, decreased stroke volume, and increased end-systolic volume.

Extra Information:

• These are the features listed on the lecture slide.

How does aortic regurgitation alter the pressure-volume loop?

Answer: It disrupts isovolumetric relaxation and produces the lecture's depicted volume-expanded loop.

Extra Information:

• The slide also lists decreased stroke volume and increased end-systolic volume.

What key pressure-volume distinction separates aortic stenosis from aortic regurgitation?

Answer: Aortic stenosis creates high outflow resistance, whereas aortic regurgitation causes diastolic backflow and loss of true isovolumetric relaxation.

Extra Information:

• The lecture lists a large pressure gradient for both lesions.

What does increased systemic vascular resistance do to afterload and cardiac output?

Answer: It increases afterload and decreases cardiac output.

Extra Information:

• Systemic vascular resistance affects the cardiac function curve.

What does increased systemic vascular resistance do to venous return?

Answer: It decreases blood return to the heart.

Extra Information:

• The lecture links this to blood being held in the arteriolar system.

Why does increased systemic vascular resistance reduce blood return to the heart?

Answer: It holds blood in the arteriolar system.

Extra Information:

• This contributes to the change in the vascular function curve.

What does decreased systemic vascular resistance do to afterload and cardiac output?

Answer: It decreases afterload and increases cardiac output.

Extra Information:

• The heart pumps against less resistance.

What does decreased systemic vascular resistance do to blood return to the heart?

Answer: It increases blood return to the heart.

Extra Information:

• This contributes to the change in the venous return curve.

Why does systemic vascular resistance change both curves on a Guyton plot?

Answer: It changes cardiac afterload and also changes blood return to the heart.

Extra Information:

• Therefore both cardiac function and vascular function are affected.

In the lecture's increased systemic vascular resistance example, what are the before and after values?

Answer: Before: CO 5.1 L/min and RAP 1.9 mmHg. After: CO 3.7 L/min and RAP 1.8 mmHg.

Extra Information:

• Cardiac output falls substantially while right atrial pressure changes very little.

What scenario produces the lecture's increased systemic vascular resistance shift?

Answer: Widespread arteriolar constriction with normal blood volume.

Extra Information:

• The scenario isolates the effect of increased systemic vascular resistance.

In the lecture's decreased systemic vascular resistance example, what are the before and after values?

Answer: Before: CO 5.1 L/min and RAP 1.9 mmHg. After: CO 7.1 L/min and RAP 2.3 mmHg.

Extra Information:

• The new equilibrium has substantially higher cardiac output.

What clinical scenario illustrates decreased systemic vascular resistance in the lecture?

Answer: Early septic shock with dilated arterioles, a warm patient, and low blood pressure.

Extra Information:

• The lecture uses this as its low-systemic-vascular-resistance example.

How does early septic shock move the Guyton equilibrium in the lecture example?

Answer: Decreased systemic vascular resistance raises cardiac output and slightly raises right atrial pressure.

Extra Information:

• CO rises from 5.1 to 7.1 L/min.
• RAP rises from 1.9 to 2.3 mmHg.

What does nitroglycerin do to the capacitance veins?

Answer: It dilates the capacitance veins.

Extra Information:

• This increases venous capacitance.

Does nitroglycerin-induced venodilation change total blood volume in the lecture example?

Answer: No. Total blood volume remains unchanged.

Extra Information:

• The lecture emphasizes where the blood is being held rather than how much blood exists.

How does nitroglycerin-induced venodilation change mean systemic filling pressure?

Answer: It lowers mean systemic filling pressure.

Extra Information:

• Greater venous capacitance produces this effect.

How does nitroglycerin shift the venous return curve?

Answer: It shifts the venous return curve down and to the left.

Extra Information:

• This occurs because greater venous capacitance lowers mean systemic filling pressure.

How does nitroglycerin affect cardiac output and right atrial pressure in the lecture example?

Answer: Both cardiac output and right atrial pressure fall.

Extra Information:

• The Guyton pattern resembles mild hemorrhage.

In the lecture's venodilation example, what are the before and after values?

Answer: Before: CO 5.1 L/min and RAP 1.9 mmHg. After: CO 4.5 L/min and RAP 0.5 mmHg.

Extra Information:

• Nitroglycerin is the example venodilator.

How are acute hemorrhage and nitroglycerin venodilation similar on a Guyton plot?

Answer: Both shift the venous return curve down and left and reduce cardiac output and right atrial pressure.

Extra Information:

• The lecture says venodilation produces the same general picture as mild hemorrhage.

How do acute hemorrhage and nitroglycerin venodilation differ mechanistically?

Answer: Hemorrhage reduces blood volume, whereas nitroglycerin increases venous capacitance without changing total blood volume.

Extra Information:

• Despite different mechanisms, both reduce venous return in the lecture examples.

What happens to contractility after acute myocardial injury or a large beta-blocker dose in the lecture scenario?

Answer: Contractility decreases.

Extra Information:

• Volume and vascular tone are unchanged in this setup.

Which curve primarily changes when contractility decreases while volume and tone are unchanged?

Answer: The cardiac function curve shifts downward.

Extra Information:

• The venous return curve remains unchanged in the lecture scenario.

How does decreased inotropy change cardiac output and right atrial pressure?

Answer: Cardiac output decreases and right atrial pressure increases.

Extra Information:

• The new equilibrium moves down and to the right.

In the lecture's decreased-inotropy example, what are the before and after values?

Answer: Before: CO 5.1 L/min and RAP 1.9 mmHg. After: CO 3.4 L/min and RAP 3.6 mmHg.

Extra Information:

• Acute myocardial injury or a large beta-blocker dose is used as the scenario.

What is point A in the lecture's heart-failure A → B → C sequence?

Answer: The normal baseline state.

Extra Information:

• One heart-failure slide gives normal as CO 5 L/min and CVP 1 mmHg.
• The later worked plot labels A as CO 5.1 L/min and RAP 1.9 mmHg.

What is point B in the lecture's heart-failure A → B → C sequence?

Answer: Uncompensated systolic heart failure.

Extra Information:

• The final worked plot labels B as CO 3.4 L/min and RAP 3.6 mmHg.

What hemodynamic change moves the system from A to B in systolic heart failure?

Answer: Loss of cardiac function lowers cardiac output and raises right atrial pressure.

Extra Information:

• The cardiac function curve shifts downward.

What reflex is triggered by the lower cardiac output in uncompensated heart failure?

Answer: Baroreceptors trigger increased sympathetic firing.

Extra Information:

• This begins the compensatory response shown in the lecture.

What hormonal response is emphasized during heart-failure compensation?

Answer: Increased renin with fluid retention.

Extra Information:

• The lecture describes the compensated state as having a lot of renin.

What vascular compensations are listed in systolic heart failure?

Answer: Venous constriction and arterial constriction.

Extra Information:

• These occur as the system moves toward the compensated state.

What happens to cardiac output and right atrial pressure as heart failure compensates from B to C?

Answer: Cardiac output improves somewhat, but right atrial pressure rises markedly.

Extra Information:

• The lecture emphasizes "better CO" together with increased RAP.

What are the A, B, and C values on the final heart-failure Guyton plot?

Answer: A: CO 5.1 L/min, RAP 1.9 mmHg. B: CO 3.4 L/min, RAP 3.6 mmHg. C: CO 3.7 L/min, RAP 6.3 mmHg.

Extra Information:

• Compensation partially improves output but produces a much higher filling pressure.

Trace the lecture's systolic heart-failure sequence from A → B → C.

Answer: Normal state → systolic failure with reduced CO and increased RAP → sympathetic and renin compensation with vasoconstriction and fluid retention → somewhat better CO but much higher RAP.

Extra Information:

• This sequence integrates the heart-failure Guyton diagrams.

What happens when a patient with chronic heart failure and volume overload receives a loop diuretic and sheds 3 L?

Answer: The venous return curve shifts down and left, lowering right atrial pressure and also lowering cardiac output in the lecture example.

Extra Information:

• The cardiac function curve remains impaired.

In the lecture's diuretic-in-heart-failure example, what are the before and after values?

Answer: Before: CO 3.4 L/min and RAP 3.6 mmHg. After: CO 2.9 L/min and RAP 1.6 mmHg.

Extra Information:

• The example follows a 3 L volume loss with a loop diuretic.

How does a diuretic affect venous return in volume-overloaded heart failure?

Answer: By reducing volume, it lowers venous return and right atrial pressure.

Extra Information:

• The lecture depicts a down-and-left shift of the venous return curve.

How would a positive inotrope affect the cardiac function curve based on the lecture's contractility diagrams?

Answer: It shifts the cardiac function curve upward.

Extra Information:

• Increased inotropy produces greater cardiac output at a given preload.

How would a drug that decreases inotropy affect the cardiac function curve?

Answer: It shifts the cardiac function curve downward.

Extra Information:

• The lecture uses a large beta-blocker dose as an example of decreased contractility.

What is the normal reference equilibrium used in the lecture's practice Guyton plot?

Answer: Cardiac output 5 L/min and right atrial pressure 2 mmHg.

Extra Information:

• The worked examples later use approximately CO 5.1 L/min and RAP 1.9 mmHg as baseline.

When analyzing a Guyton problem, what two questions should you ask first?

Answer: Which curve changes, and in what direction?

Extra Information:

• Then locate the new intersection.
• The new intersection gives the new cardiac output and right atrial pressure.

If the venous return curve shifts right and up while the cardiac function curve is unchanged, what happens to equilibrium cardiac output and right atrial pressure?

Answer: Both increase.

Extra Information:

• This is the pattern shown with increased blood or plasma volume.

If the venous return curve shifts left and down while the cardiac function curve is unchanged, what happens to equilibrium cardiac output and right atrial pressure?

Answer: Both decrease.

Extra Information:

• This is the pattern shown with hypovolemia and venodilation.

If the cardiac function curve shifts downward while venous return is unchanged, what happens to equilibrium cardiac output and right atrial pressure?

Answer: Cardiac output decreases and right atrial pressure increases.

Extra Information:

• This is the decreased-inotropy pattern.

Compare the Guyton effects of increased blood volume and increased contractility.

Answer: Increased blood volume shifts the venous return curve up and right, whereas increased contractility shifts the cardiac function curve upward.

Extra Information:

• Both can increase cardiac output.
• They act through different curves.

Compare the Guyton effects of hemorrhage and decreased contractility.

Answer: Hemorrhage shifts the venous return curve down and left and lowers both CO and RAP, whereas decreased contractility shifts the cardiac function curve downward, lowering CO but raising RAP.

Extra Information:

• The opposite RAP responses help distinguish the two mechanisms.

Compare the Guyton effects of increased versus decreased systemic vascular resistance.

Answer: Increased systemic vascular resistance raises afterload and reduces blood return, lowering cardiac output. Decreased systemic vascular resistance lowers afterload and increases blood return, raising cardiac output.

Extra Information:

• Systemic vascular resistance changes both cardiac and vascular function curves.

What does the lecture mean by cardiovascular equilibrium?

Answer: The operating point where cardiac output equals venous return.

Extra Information:

• A change in either curve creates a new intersection.
• The new intersection determines the new cardiac output and right atrial pressure.