Cardiac Output and Regulation Practice Questions
20 free Cardiac Output and Regulation practice questions for the Physiology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following equations correctly defines Cardiac Output (CO)?
- A CO = Stroke Volume / Heart Rate
- B CO = Mean Arterial Pressure × Total Peripheral Resistance
- C CO = End-Diastolic Volume - End-Systolic Volume
- D CO = Heart Rate × Stroke Volume
Correct answer: CO = Heart Rate × Stroke Volume
Cardiac output is the volume of blood pumped by each ventricle per minute. It is the product of the heart rate (beats/min) and the stroke volume (volume ejected per beat).
According to the Frank-Starling Law of the heart, an increase in venous return leads to an increase in stroke volume primarily due to:
- A Increased sympathetic nervous system activity
- B Decreased afterload in the systemic circulation
- C Increased calcium influx through L-type channels
- D Stretching of myocardial fibers by increased EDV
Correct answer: Stretching of myocardial fibers by increased EDV
The Frank-Starling mechanism describes the intrinsic ability of the heart to adapt to increasing volumes of inflowing blood. Increased stretch of the ventricular muscle fibers (preload) leads to more optimal actin-myosin overlap and a more forceful contraction.
Which of the following factors would decrease cardiac output by increasing 'afterload'?
- A Severe systemic hypertension
- B Increased venous return
- C Infusion of a positive inotropic agent
- D Dilation of the arterioles
Correct answer: Severe systemic hypertension
Afterload is the 'load' or resistance that the heart must pump against to eject blood. Systemic hypertension increases the pressure in the aorta, making it harder for the left ventricle to open the aortic valve and eject its stroke volume.
Sympathetic stimulation of the heart increases contractility (positive inotropy) by which molecular mechanism?
- A Increasing the permeability of K+ channels
- B Activating the inhibitory G-protein (Gi)
- C Raising cAMP to activate Protein Kinase A
- D Inhibiting the Na+/K+ ATPase pump
Correct answer: Raising cAMP to activate Protein Kinase A
Norepinephrine binds to beta-1 receptors, activating adenylyl cyclase to produce cAMP. cAMP activates Protein Kinase A, which phosphorylates calcium channels and phospholamban, resulting in higher intracellular calcium and faster calcium reuptake.
The 'Bainbridge Reflex' (atrial reflex) describes an increase in heart rate in response to:
- A A sudden drop in mean arterial pressure
- B Increased pressure in the carotid sinus
- C Venous return stretching the right atrium
- D Hypoxia sensed by peripheral chemoreceptors
Correct answer: Venous return stretching the right atrium
The Bainbridge reflex is a compensatory mechanism where an increase in central venous pressure stretches atrial stretch receptors. This sends signals to the medulla to increase sympathetic output and heart rate to help pump the excess blood through the system.
Ejection Fraction (EF) is a clinical measure of cardiac function. How is it calculated?
- A (Stroke Volume / End-Diastolic Volume) × 100
- B (Stroke Volume / End-Systolic Volume) × 100
- C (End-Diastolic Volume / Stroke Volume) × 100
- D (End-Systolic Volume / End-Diastolic Volume) × 100
Correct answer: (Stroke Volume / End-Diastolic Volume) × 100
Ejection fraction represents the percentage of blood pumped out of the filled ventricle with each beat. A normal EF is typically between 55% and 70%.
Which of the following would be considered a 'Negative Inotropic' agent?
- A Digitalis (digoxin)
- B Dopamine (a catecholamine)
- C Calcium channel blockers
- D Epinephrine (adrenaline)
Correct answer: Calcium channel blockers
Negative inotropic agents decrease the force of muscular contraction. Calcium channel blockers reduce the amount of calcium available for the contractile machinery, thereby weakening the strength of contraction.
During heavy exercise, why does cardiac output increase significantly even though diastole (filling time) is shortened?
- A The Frank-Starling mechanism is inhibited
- B The heart rate remains low while stroke volume triples
- C Peripheral resistance increases to force more blood into the heart
- D Increased contractility and venous return compensate
Correct answer: Increased contractility and venous return compensate
During exercise, sympathetic activity increases heart rate and contractility (inotropy). Simultaneously, the skeletal muscle pump and respiratory pump increase venous return, maintaining stroke volume despite a shorter diastolic interval.
The Fick Principle for measuring cardiac output is based on which of the following?
- A Oxygen consumption and the arteriovenous O2 content difference
- B The rate of pressure change in the aorta
- C The time it takes for a dye to travel from the arm to the tongue
- D The volume of the heart measured by ultrasound
Correct answer: Oxygen consumption and the arteriovenous O2 content difference
The Fick Principle states that the uptake of a substance (like O2) by an organ is the product of the blood flow to that organ and the arteriovenous concentration difference of the substance.
Which phase of the cardiac cycle is most affected by a decrease in preload?
- A Ventricular ejection
- B Isovolumetric contraction
- C Isovolumetric relaxation
- D Ventricular filling
Correct answer: Ventricular ejection
A decrease in preload (venous return) results in a lower end-diastolic volume. According to the Frank-Starling law, this leads to a less forceful contraction and a smaller stroke volume during the ventricular ejection phase.
Parasympathetic (vagal) stimulation has a significant negative chronotropic effect but minimal inotropic effect. Why is this?
- A Vagal fibers innervate the SA/AV nodes, not the ventricles
- B The ventricles lack M2 muscarinic receptors
- C Acetylcholine increases calcium influx into the ventricles
- D The vagus nerve only carries sensory information from the heart
Correct answer: Vagal fibers innervate the SA/AV nodes, not the ventricles
The vagus nerve heavily innervates the conduction tissues (SA and AV nodes), which strongly regulates heart rate. Because it provides relatively little innervation to the ventricular myocardium, it has much less impact on contractility compared to sympathetic nerves.
What is the effect of 'Digitalis' (cardiac glycosides) on cardiac output in a failing heart?
- A It increases CO by inhibiting Na+/K+ pump, raising calcium
- B It decreases CO by slowing the heart rate too much
- C It decreases CO by dilating all peripheral blood vessels
- D It has no effect on CO but improves lung function
Correct answer: It increases CO by inhibiting Na+/K+ pump, raising calcium
Digitalis inhibits the Na+/K+ ATPase, which increases intracellular sodium. This slows the Na+/Ca2+ exchanger, resulting in higher intracellular calcium levels and increased force of contraction (positive inotropy).
Preload is most accurately estimated by measuring which of the following clinical parameters?
- A Mean Arterial Pressure (MAP) value
- B Total Peripheral Resistance (TPR) value
- C Left Ventricular End-Diastolic Pressure
- D Systolic Blood Pressure value
Correct answer: Left Ventricular End-Diastolic Pressure
Preload refers to the stretch of the ventricular wall at the end of diastole. Clinically, this is estimated by measuring the pressure in the ventricle at the end of filling (LVEDP) or the pulmonary capillary wedge pressure.
Which of the following will result in a DECREASE in stroke volume?
- A Increased venous return
- B Decreased afterload
- C Increased parasympathetic tone to the nodes
- D Increased sympathetic stimulation of the ventricles
Correct answer: Increased parasympathetic tone to the nodes
Parasympathetic (vagal) stimulation to the SA and AV nodes slows heart rate, and by the reverse of the Treppe (Bowditch) effect, the slower rate gives the cell more time to clear intracellular calcium between beats, leaving less calcium available for the next contraction. This lowers ventricular contractility and therefore stroke volume. The other options all act to raise stroke volume: increased venous return raises preload, decreased afterload eases ejection, and increased sympathetic stimulation boosts contractility.
The 'Treppe effect' (or staircase phenomenon) explains that an increase in heart rate leads to an increase in contractility because:
- A The heart muscle simply generates more heat with faster beating
- B There is an accumulation of intracellular calcium over several beats
- C The Frank-Starling mechanism is more active at higher heart rates
- D The ventricles are given noticeably more time to fill between beats
Correct answer: There is an accumulation of intracellular calcium over several beats
When the heart rate increases, the sodium/potassium pump cannot keep up, and more calcium enters the cell during the frequent action potentials than can be removed during the shorter diastole, leading to a stronger contraction.
During the baroreceptor reflex, a decrease in blood pressure leads to an increase in cardiac output. What is the effector response?
- A Increased vagal tone and decreased sympathetic tone
- B Decreased vagal tone and increased sympathetic tone
- C Dilation of all systemic arterioles
- D Decreased release of Epinephrine from the adrenal medulla
Correct answer: Decreased vagal tone and increased sympathetic tone
When blood pressure drops, baroreceptor firing decreases. The medulla responds by inhibiting parasympathetic output (lifting the brake) and stimulating sympathetic output (pressing the gas) to increase heart rate and contractility.
What happens to the Cardiac Output curve in a patient with myocardial infarction?
- A The curve shifts upward and to the left
- B The curve remains the same but the venous return curve shifts
- C The curve shifts downward and to the right
- D The curve becomes a vertical line
Correct answer: The curve shifts downward and to the right
A myocardial infarction damages the heart muscle, reducing its pumping efficacy (contractility). This is represented by a downward shift of the cardiac output curve, meaning lower CO for any given right atrial pressure.
The 'Respiratory Pump' aids in increasing cardiac output by:
- A Increasing intrathoracic pressure during inspiration
- B Decreasing intrathoracic pressure during inspiration
- C Increasing the resistance of the pulmonary arteries
- D Reducing the work of the diaphragm
Correct answer: Decreasing intrathoracic pressure during inspiration
During inspiration, the chest cavity expands and intrathoracic pressure drops. This creates a pressure gradient that facilitates the flow of venous blood from the abdomen into the thorax and right atrium, increasing preload.
Which of the following would cause a 'Hypereffective' heart (shifting the CO curve upward)?
- A Severe aortic valvular stenosis
- B Sympathetic stimulation and hypertrophy
- C Excessive chronic parasympathetic stimulation
- D Acute myocarditis with reduced contractility
Correct answer: Sympathetic stimulation and hypertrophy
A hypereffective heart is one that can pump much more blood than normal. This is typically achieved through a combination of sympathetic nervous stimulation (increased rate/strength) and cardiac hypertrophy (e.g., in marathon runners).
The resting cardiac output of a typical 70 kg adult is approximately:
- A 2 L/min
- B 5 L/min
- C 10 L/min
- D 15 L/min
Correct answer: 5 L/min
In a healthy adult at rest, the heart rate is about 70-75 bpm and stroke volume is about 70 mL, resulting in a cardiac output of roughly 5 liters per minute.