Physiology Lecture 19: Cardiac Output

Which chamber of the heart does cardiac output typically reference?

Left Ventricle

Is resting ejection fraction predictive of activity tolerance?

No

What are the major cardiac factors that affect cardiac output?

1. Heart Rate

2. Myocardial Contractility

What are the major coupling factors that affect cardiac output?

1. Preload

2. Afterload

What is the volume of the blood at the end of diastole?

Preload

What is preload primarily a reflection of?

Venous Return

Which pressures are used to indirectly measure preload?

1. CVP (Right Atrium)

2. PCWP (Left Atrium)

Does more preload lead to more or less myocardial stretch (Frank Starling Law)?

More

Does more preload lead to more or less contraction speed and power (Frank Starling Law)?

More

What restricts preload overfilling?

Pericardium

What factors can increase preload?

1. Compression Pumps

2. IV Fluids

3. Muscle Activity

4. Vasopressin

What factors can decrease preload?

1. Diuretics

2. Nitrates

3. Vascular Incompetence

What relationships are linked with Frank Starling Law?

Length and Tension

According to the Frank Starling Law, the energy of contraction is proportional to what?

Muscle fiber length at rest

Which pressures are used to estimate afterload?

1. PAP (Right Ventricle)

2. Systemic (Left Ventricle)

What are the factors that affect afterload?

1. Intra-Ventricular Pressure

2. Chamber Size

3. Wall Thickness

According to LaPlace Law, how does a thicker ventricle wall affect wall stress?

Less wall stress (Less oxygen consumption)

Which contraction causes the highest tension of ventricles?

Isovolumetric Contraction

What is the equation between wall tension, radius, and pressure in LaPlace Law?

P = 2T / R

How is cardiac output affected by afterload changes above 170 mmHg?

Significant decrease in CO

What must isometric contraction exceed to open semilunar valves?

Arterial diastolic pressure

How does high pressure in arterial vessels during ventricular diastole affect stroke volume?

Decreases stroke volume

How does increased heart rate affect diastolic period and preload?

Decreases

How does increased heart rate affect stroke volume?

Decreases stroke volume

How does increased heart rate affect cardiac output?

Increases to a maximum point and then declines

What action causes contraction of the heart?

Shortening of myofilaments

Do necrotic tissues contract?

No

What are the factors that affect contractility of the heart?

1. Myocardial health

2. Chamber size

3. Preload/afterload

4. SNS

5. Medications

Does contractility increase with heart rate?

Yes, to a point

Why does afterload increase with contracility?

To compensate for increased ESV and decreased SV

How do inotropic agents increase myocardial contracility?

Increasing intracellular calcium concentration in myocardial muscle cells

If the SNS increases contractility, how does this affect heart pumping?

1. Faster ejection

2. Shorter ejection time

3. Less EDV (More EF)

What factors determine filling of the left ventricle?

1. CVP (Right Atrium)

2. Right Ventricle Stroke Volume

How does preload increasing affect the stroke work curve?

Increases

Does the right or left part of the heart perform more pressure-volume work?

Left

If atrial pressure is too high, what diseases may develop?

1. Hypertension

2. Ventricle hypertrophy

3. Pulmonary Edema

How does high atrial pressure affect oxygen demand?

Increases oxygen demand

If atrial pressure is too low, what diseases may develop?

1. Collapsed veins

2. Systemic edema

How does low atrial pressure affect vascular resistance to sustain preload?

Increases resistance

How does low atrial pressure affect microvascular blood pressure?

Increases pressure

Does the parasympathetic nervous system have a lot of effect on the heart?

No

What are the only parts of the heart that the parasympathetic nervous system can affect?

Nodes (Atria, SA, AV)

Does having a normal curve or having zero sympathetic effect decrease cardiac output more?

Zero sympathetics

Does having no sympathetic effect or having parasympathetic effect decrease cardiac output more?

Having parasympathetic effect