40 Questions
What is the primary factor determining preload in the heart?
Venous vascular volume
According to the Frank-Starling law, what is the relationship between the volume of blood in the heart and the force of contraction?
Direct relationship
What is the term for the pressure or tension work of the heart?
Afterload
What is the maximum force of contraction achieved when muscle fibers are stretched to?
2.5 times their resting length
Which of the following can decrease preload?
Obstruction to blood returning to the heart
What is the primary cause of increased afterload in the right ventricle?
Increased pulmonary vascular resistance
What is the term for the force that the contracting heart must generate to eject blood from the filled heart?
Afterload
Why may the failing or dilated heart not respond to increased filling?
Because its fibers are already lengthened maximally
What is the primary component of afterload that affects cardiac output?
Systemic vascular resistance
Which of the following does not increase contractility of the heart?
Beta blockers
What is the primary difference between primary and secondary hypertension?
Primary hypertension is caused by a systemic disease process, while secondary hypertension is not.
What is the relationship between systemic vascular resistance and ventricular oxygen consumption?
Directly proportional
Which of the following is NOT a target organ for hypertension?
Lungs
What is the effect of chronic hypertension on systemic blood vessels?
It causes hypertrophy and hyperplasia of the tunica intima and media.
Which of the following is a negative inotrope that decreases contractility of the heart?
Hypoxia
What is the definition of malignant hypertension?
A type of hypertension that is rapid and progressive, with diastolic pressure usually above 140 mm Hg.
What is the primary factor that determines cardiac output?
Stroke volume
What is the chief cause of isolated systolic hypertension (ISH) in the elderly?
Rigidity of proximal large arteries.
Which of the following increases cardiac output by increasing stroke volume?
Increase in contractility
What is the relationship between afterload and intra-ventricular pressure?
Directly proportional
What is the effect of increased cardiac output on blood pressure?
It increases blood pressure.
Which of the following is an example of a factor that affects cardiac output by modifying contractility?
Sympathetic stimulation
What is the effect of hypertension on the eyes?
It causes changes in the vascular bed, noted by viewing the arterioles of the retina.
What is the term for the damage caused to organs due to chronic hypertension?
Target organ damage.
What is the primary determinant of cardiac output according to the Frank-Starling law?
End-diastolic volume (EDV)
Which of the following increases preload?
Increased venous return
What is the formula for calculating cardiac output?
CO = SV x HR
What is the primary factor affecting contractility of the heart?
Interaction of actin and myosin filaments
What is the normal range of cardiac output in liters per minute?
4.2-8 L/min
Which of the following increases right ventricular afterload?
Increase in pulmonary vascular resistance
What is the term for the amount of blood ejected from the heart with each beat?
Stroke volume (SV)
What is the term for the resistance to ejection of blood from the heart?
Afterload
What is the main difference between primary and secondary hypertension?
Primary hypertension affects 90-95% of individuals, whereas secondary hypertension affects the remaining 5-10%.
Which of the following best describes the Frank-Starling law?
The law states that the force of contraction of the heart is directly proportional to the volume of blood in the heart.
What is the primary cause of increased afterload in the right ventricle?
Increased peripheral vascular resistance.
Which of the following factors can increase cardiac output?
Increased heart rate.
What is the term for the force that the contracting heart must generate to eject blood from the filled heart?
Afterload.
What is the main consequence of sustained hypertension?
Target organ damage.
What is the term for the pressure or tension work of the heart?
Cardiac work.
Which of the following is a factor that can decrease cardiac output?
Increased peripheral vascular resistance.
Study Notes
Cardiac Output and Blood Pressure
- Cardiac output (CO) is the amount of blood the heart ejects in a minute, ranging from 4.2 to 8 Liters.
- CO varies with activity, age, and gender.
- CO depends on stroke volume (SV) and heart rate (HR).
Factors Affecting Cardiac Output
- Preload (or filling of the ventricles): determined by venous return to the heart and the accompanying stretch of muscle fibers.
- Afterload (or resistance to ejection of blood from the heart): determined by systemic vascular resistance (SVR).
- Contractility (intrinsic ability of the heart muscle to contract): determined by biochemical and biophysical properties governing actin and myosin interactions.
Preload and Afterload
- Preload represents the volume work of the heart, imposed before the contraction begins.
- Afterload represents the pressure or tension work of the heart, generated to move blood into the aorta.
Contractility and Inotropes
- Contractility refers to the ability of the heart to change its force of contraction without changing its resting length.
- Positive inotropes (e.g., sympathetic stimulation, dopamine, epinephrine, norepinephrine) increase contractility.
- Negative inotropes (e.g., beta blockers, hypoxia, alcohol, glucose, inflammatory mediators) decrease contractility.
Blood Pressure and Hypertension
- Blood pressure (BP) is determined by cardiac output and systemic vascular resistance.
- Hypertension is a sustained elevation of arterial blood pressure, diagnosed when average BP measurements are 140/90 mmHg or higher.
- Types of hypertension: primary (essential or idiopathic), secondary (caused by systemic disease), and isolated (e.g., systolic hypertension).
Secondary Hypertension
- Caused by systemic disease processes that raise peripheral vascular resistance (PVR) or cardiac output.
- If the cause is identified and removed before permanent structural damage occurs, BP can return to normal.
Complications of Hypertension
- Chronic hypertension damages systemic blood vessels, leading to vascular remodeling and eventual organ dysfunction.
- Target organs affected: kidney, brain, heart, extremities, and eyes.
- Complications: left ventricular hypertrophy (LVH), heart failure, coronary artery disease (CAD), myocardial infarction (MI), stroke, and renal failure.
Isolated Systolic Hypertension and Malignant Hypertension
- Isolated systolic hypertension (ISH) can be caused by increased cardiac output, aortic valve dysfunction, thyroid storm, or beriberi (thiamine deficiency).
- Malignant hypertension is a rapidly progressive form, characterized by diastolic pressure above 140 mmHg, leading to encephalopathy, cerebral edema, and loss of consciousness.
This quiz covers the concept of afterload in cardiovascular physiology, its relation to systemic vascular resistance, and its effect on cardiac output and ventricular oxygen consumption.
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