Determination of Cardiac Output

Multiple Choice Questions (MCQs)

1. What is the principle of the Direct Fick Method for measuring cardiac output?
   a) The electromotive force generated in a magnetic field is proportional to blood flow.
   b) The volume of fluid can be calculated based on the concentration of a known substance.
   c) The amount of a substance taken up by circulation equals the arterio-venous difference multiplied by blood flow.
   d) The area under the dye dilution curve is proportional to blood flow.
   Answer: c) The amount of a substance taken up by circulation equals the arterio-venous difference multiplied by blood flow.
2. What is required to calculate cardiac output using the Direct Fick Method?
   a) Area under the dye dilution curve
   b) Oxygen consumption and arterio-venous oxygen difference
   c) Electromotive force and vessel diameter
   d) Blood temperature and pressure
   Answer: b) Oxygen consumption and arterio-venous oxygen difference
3. What is the principle of the Indicator Dilution Method?
   a) Electromotive force is proportional to blood flow.
   b) Blood flow is calculated using oxygen uptake and AV O₂ difference.
   c) The volume of fluid is determined by the concentration of a known substance.
   d) The pressure gradient across the heart is measured.
   Answer: c) The volume of fluid is determined by the concentration of a known substance.
4. Which indicator is commonly used in the Indicator Dilution Method?
   a) Oxygen
   b) Cardio green dye
   c) Magnetic isotopes
   d) Thermistor probes
   Answer: b) Cardio green dye
5. In the Flowmeter Method, what is proportional to blood flow?
   a) Dye concentration
   b) Area under the curve
   c) Electromotive force
   d) Oxygen consumption
   Answer: c) Electromotive force
6. Which method measures cardiac output using the dye dilution curve?
   a) Direct Fick Method
   b) Flowmeter Method
   c) Indicator Dilution Method
   d) Thermodilution Method
   Answer: c) Indicator Dilution Method
7. Where is the flowmeter probe placed in the Flowmeter Method?
   a) Pulmonary artery
   b) Root of the aorta
   c) Right atrium
   d) Left ventricle
   Answer: b) Root of the aorta
8. What factor can increase cardiac output up to 4–6 times?
   a) Stress
   b) Pregnancy
   c) Muscular exercise
   d) Hypoxia
   Answer: c) Muscular exercise
9. What happens to cardiac output during rest or inactivity?
   a) Increases
   b) Decreases
   c) Remains unchanged
   d) Fluctuates
   Answer: b) Decreases
10. What is the primary limitation of the Direct Fick Method?
    a) Requires specialized magnetic equipment
    b) Invasive arterial and venous sampling
    c) Limited use in patients with heart disease
    d) Relies on temperature changes
    Answer: b) Invasive arterial and venous sampling

Fill in the Blanks

1. The Direct Fick Method calculates cardiac output using oxygen consumption and ________.
   Answer: arterio-venous oxygen difference
2. In the Indicator Dilution Method, the area under the ________ curve represents one complete circulation of the dye.
   Answer: dye dilution
3. The Flowmeter Method measures the ________ generated as blood flows through a magnetic field.
   Answer: electromotive force
4. Cardiac output increases 4–6 times during ________.
   Answer: muscular exercise
5. During rest or inactivity, cardiac output typically ________.
   Answer: decreases

True or False

1. The Direct Fick Method requires the measurement of oxygen consumption per minute.
   Answer: True
2. The Flowmeter Method measures cardiac output using dye injection and concentration curves.
   Answer: False
3. Hypoxia can cause an increase in cardiac output.
   Answer: True
4. In the Indicator Dilution Method, the indicator is injected into an artery.
   Answer: False
5. Pregnancy typically decreases cardiac output.
   Answer: False

Subjective Questions

1. Compare the Direct Fick Method and Indicator Dilution Method for measuring cardiac output.
   Answer:
   • Direct Fick Method: Based on oxygen consumption and arterio-venous oxygen difference. It is accurate but invasive, requiring arterial and venous blood sampling. Suitable for research or clinical use when precise measurements are necessary.
   • Indicator Dilution Method: Uses the concentration of a known indicator (e.g., dye) injected into a vein and measures its dilution over time. It is less invasive than the Fick Method but requires careful timing and interpretation of the dye dilution curve.
2. Explain factors that can influence cardiac output.
   Answer:
   • Increase in Cardiac Output:
     • Muscular exercise: 4–6 times increase due to heightened oxygen demand.
     • Pregnancy: Increased metabolic demands and blood volume.
     • Hypoxia: Compensatory increase to enhance oxygen delivery.
     • Stress and elevated body temperature.
   • Decrease in Cardiac Output:
     • Rest or inactivity: Reduced metabolic demand.
     • Certain heart diseases: Reduced pumping efficiency due to structural or functional impairments.
       These factors demonstrate how cardiac output adjusts to meet physiological and pathological conditions.