Physiology of Breathing and Gas Exchange
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Questions and Answers

Which is not true regarding the work of breathing?

  • Minimum work requires higher rates of breathing in obstructive lung disease.
  • Minimum work is performed at higher frequencies with stiff lungs.
  • Total work of breathing in normal lungs is approximately 15 breaths/min. (correct)
  • Total work is equal to the work required to overcome airflow plus elastic resistance.

    • Under resting metabolic conditions, a healthy adult produces approximately how much CO2 per minute?

    200 ml/min

    Which of the following does not describe hypoventilation?

  • Alveolar ventilation is less than CO2 production.
  • Low blood pH.
  • High CO2 level in the blood.
  • Alveolar ventilation is more than CO2 production. (correct)

    • Regarding distribution of ventilation, which is not true?

    <p>The lung has a V/Q ratio of 1.</p> Signup and view all the answers

    Which is not correct regarding the distribution of ventilation?

    <p>Alveoli at the apexes expand more during inspiration.</p> Signup and view all the answers

    A lung unit has a short time constant if compliance or resistance is high.

    <p>False</p> Signup and view all the answers

    Which of the following constitute the physiologic dead space?

    <p>Anatomic dead space plus alveolar dead space</p> Signup and view all the answers

    Which is the formula for minute ventilation?

    <p>Tidal volume x frequency of breathing</p> Signup and view all the answers

    For a healthy adult breathing 16 breaths/min and having a VT of 450 ml, what is the minute ventilation?

    <p>7.2 L/minute</p> Signup and view all the answers

    In a healthy adult with a tidal volume of 500 ml, how much fresh gas goes to the alveoli for gas exchange?

    <p>350 ml</p> Signup and view all the answers

    The normal dead space ratio is approximately how much?

    <p>30% (20-40%)</p> Signup and view all the answers

    The physical tendency of an object to return to an initial state after deformation refers to which of the following?

    <p>Elasticity</p> Signup and view all the answers

    Correct statement regarding resistance:

    <p>Airway resistance decreases as lung volume increases.</p> Signup and view all the answers

    Which is not true regarding the pressure differences during breathing?

    <p>During a normal breathing cycle, the glottis remains closed.</p> Signup and view all the answers

    At functional residual capacity (FRC), which is not true?

    <p>Airway opening and alveolar pressures are both zero.</p> Signup and view all the answers

    In patients with increased airflow resistance (obstructive lung disease), to maintain minimum work of breathing, patients tend to breathe at this rate:

    <p>Slower</p> Signup and view all the answers

    Applying the effect of gravity on ventilation and blood flow, to improve oxygenation in a patient with a diseased left lung, the patient should be placed on which side?

    <p>Right side down</p> Signup and view all the answers

    Which is the formula for minute ventilation?

    <p>Rate of breathing (fB) x tidal volume (VT)</p> Signup and view all the answers

    Which is the formula for computing the volume of gas reaching the alveoli (alveolar volume) in a healthy adult?

    <p>Tidal volume (VT) - anatomic dead space (VD anatomic)</p> Signup and view all the answers

    To accurately assess the alveolar ventilation in clinical practice, which is the preferred formula?

    <p>Alveolar ventilation = fB (tidal volume - physiologic dead space)</p> Signup and view all the answers

    NOT TRUE regarding lung compliance:

    <p>Obesity and kyphoscoliosis increase combined compliance.</p> Signup and view all the answers

    Regarding the distribution of resistance, which is true?

    <p>Resistance decreases with increased lung volume.</p> Signup and view all the answers

    Study Notes

    Work of Breathing

    • Increased airflow resistance (obstructive lung disease) requires higher breathing rates for minimal work.
    • Normal lungs have minimal work of breathing at approximately 15 breaths/minute.
    • The work of overcoming airflow and elastic resistance equals the total work of breathing.
    • Stiff lungs (increased elastic resistance) require higher frequencies for minimal work.

    Carbon Dioxide Production

    • A healthy adult produces approximately 200 ml/min of CO2 under resting conditions.

    Hypoventilation

    • Alveolar ventilation (CO2 removal) less than CO2 production.
    • Low blood pH
    • High CO2 level in the blood.

    Distribution of Ventilation

    • Lungs have uneven ventilation in proportion to perfusion.
    • Differences in thoracic expansion and transpulmonary pressure gradients cause uneven distribution.
    • Though the lung is essential for gas exchange, it does not have a perfect ventilation-perfusion ratio (V/Q) of 1.
    • The lower chest expands approximately 50% more than the upper chest.

    Distribution of Ventilation (cont.)

    • Alveoli at the lung base expand more than alveoli at the apex.
    • Alveoli at the apex have a larger resting volume than those at the base.
    • Greater transpulmonary pressure gradient at the top of the upright lung.
    • Alveoli at the apex expand more during inspiration.

    Time Constant

    • A lung unit has a short time constant if compliance or resistance is high.

    Physiologic Dead Space

    • The sum of anatomic and alveolar dead space.

    Minute Ventilation

    • The product of tidal volume and frequency of breathing.

    Alveolar Ventilation

    • Approximately 350 ml of fresh gas goes to the alveoli for gas exchange in a healthy adult with a tidal volume of 500 ml.

    Dead Space Ratio

    • Approximately 30% (20-40%).

    Elasticity

    • The physical tendency of an object to return to its initial state after deformation.

    Resistance

    • Resistance is lowest in the upper airways.
    • Airway resistance decreases as lung volume increases due to airway distension during lung inflation.
    • The total resistance is highest in the smaller airways because they are arranged in parallel.

    Pressure During Breathing

    • During a normal breathing cycle, the glottis remains open.
    • The pressure at the surface of the body (PBS) and PAO remain at zero (atmospheric) throughout the cycle.
    • A zero pressure in the trachea is equivalent to atmospheric pressure.
    • Alveolar pressure (PA) is sub-atmospheric at the beginning of inspiration compared to the pressure at the airway opening (PAO).

    Functional Residual Capacity (FRC)

    • At FRC, the lung is at its resting volume.
    • Trans-airway pressure gradient is also zero.
    • Air flows out of the airway opening.
    • Airway opening and alveolar pressures are both zero.

    Minimum Work of Breathing in Obstructive Lung Disease

    • To maintain minimal work of breathing, patients with increased airflow resistance (obstructive lung disease) tend to breathe at a slower rate.

    Improving Oxygenation with Lung Disease

    • To improve oxygenation in a patient with a diseased left lung, the patient should be placed lying with the right side down, applying the effect of gravity on ventilation and blood flow (perfusion).

    Alveolar Volume Computation

    • Tidal volume (VT) minus anatomic dead space (VD anatomic)

    Alveolar Ventilation Computation (Clinical Practice)

    • Alveolar ventilation = Frequency (fB) x (Tidal volume - physiologic dead space)

    Lung Compliance

    • The combined compliance of the lung-chest wall system is approximately half that of the individual components.
    • Obesity and kyphoscoliosis increase the combined compliance.
    • In healthy adults, the compliance of the lungs and chest wall are each approximately 0.2 L/cm H2O.
    • The lungs and chest wall each have their own compliance or distensibility.

    Distribution of Resistance

    • Considering the number of airways at each level, the majority of airway resistance comes from the smaller airways.
    • This is because the smaller airways are arranged in parallel.

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    Description

    This quiz explores the mechanics of breathing, including airflow resistance and CO2 production in healthy adults. It covers concepts such as hypoventilation and the uneven distribution of ventilation in the lungs, providing insight into the pulmonary function necessary for effective gas exchange.

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