Pressure Difference Generation and Boyle's Law Quiz
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Questions and Answers

What happens to the chest wall recoil at lung volumes above 70% TLC?

  • It remains neutral.
  • It becomes outward.
  • It ceases to recoil.
  • It becomes inward. (correct)

    • How does the integrity disturbance like pneumothorax affect alveoli?

  • Alveoli lose surfactant.
  • Alveoli tend to collapse. (correct)
  • Alveoli become stiff.
  • Alveoli expand.

    • What happens to airway resistance with increasing lung volume?

  • Airway resistance increases.
  • Airway resistance remains constant.
  • Airway resistance becomes maximal.
  • Airway resistance decreases. (correct)

    • What is the Equal Pressure Point during forced expiration?

    <p>The point where airway pressure equals surrounding peribronchial pressure.</p> Signup and view all the answers

    Why does emphysema lead to difficulty in achieving high airflow rates?

    <p>Decreased alveolar elastic recoil.</p> Signup and view all the answers

    What opposes dynamic compression of airways during forced expiration?

    <p>Alveolar elastic recoil pressure.</p> Signup and view all the answers

    What is the main role of pulmonary surfactant in the lungs?

    <p>Decrease surface tension</p> Signup and view all the answers

    According to La Place's law, what is the relationship between pressure (P), surface tension (T), and radius (r) in a spherical bubble?

    <p>P is directly proportional to T and inversely proportional to r</p> Signup and view all the answers

    How does pulmonary surfactant affect alveolar stability?

    <p>Decreases surface tension in smaller alveoli</p> Signup and view all the answers

    What happens to surface tension during inspiration in the lungs?

    <p>Increases due to higher surfactant concentration</p> Signup and view all the answers

    How does surfactant deficiency contribute to respiratory distress syndrome?

    <p>Results in atelectasis and hypoxemia</p> Signup and view all the answers

    What is the effect of surfactant on alveolar compliance?

    <p>Increases compliance by reducing surface tension</p> Signup and view all the answers

    In the context of alveolar interdependence, what stabilizes alveoli and prevents collapse?

    <p>Mechanical interdependence and elastic septa</p> Signup and view all the answers

    What would happen if two nearby alveoli with different radii have the same surface tension according to La Place's law?

    <p>The alveolus with the smaller radius would generate higher internal pressure</p> Signup and view all the answers

    What is the primary function of pulmonary surfactant on alveolar walls?

    <p>Decrease surface tension.</p> Signup and view all the answers

    How does surfactant contribute to maintaining lung compliance?

    <p>By decreasing surface tension.</p> Signup and view all the answers

    What is the main function of pulmonary surfactant?

    <p>Decrease surface tension in the alveoli</p> Signup and view all the answers

    In the context of alveolar stability, what happens to alveoli during inspiration?

    <p>Alveoli expand passively in response to increased transmural pressure</p> Signup and view all the answers

    What is the relationship between lung volume and airway pressure during quiet expiration?

    <p>Increased lung volume increases airway pressure</p> Signup and view all the answers

    How does a negative intrapleural pressure affect alveolar stability at functional residual capacity (FRC)?

    <p>Assists in keeping the lungs expanded</p> Signup and view all the answers

    What is the impact of surface tension on alveolar stability?

    <p>Surface tension prevents alveolar collapse</p> Signup and view all the answers

    According to Laplace's law, how does surface tension affect small alveoli compared to large alveoli?

    <p>Surface tension increases in small alveoli</p> Signup and view all the answers

    What happens to airway pressure when lung volume decreases during expiration?

    <p>Airway pressure increases above atmospheric pressure</p> Signup and view all the answers

    How does negative pressure breathing differ from positive pressure breathing?

    <p>Negative pressure breathing involves air moving into the lungs due to atmospheric pressure exceeding airway pressure</p> Signup and view all the answers

    Study Notes

    Boyle's Law

    • States that pressure is inversely proportional to volume at a constant temperature
    • Mathematical expression: P1V1 = P2V2
    • Examples:
      • Pre-inspiration: V = 3L, P = 4 mmHg
      • Inspiration: V = 4L, P = 3 mmHg
      • Active Expiration: V = 2L, P = 6 mmHg

    Inspiration and Expiration

    • Inspiration is an active process
    • Lungs passively expand
    • Air will move from a high-pressure area to a low-pressure area (pressure gradient)
    • No pressure difference = no movement
    • Pressure difference must be sufficient to overcome the resistance to airflow offered by the conducting airways

    Pressure Gradient and Air Movement

    • Airway pressure equals ambient air pressure (barometric pressure) down to alveoli at end-expiration
    • Alveolar pressure is considered 0 cm H2O pressure at end-expiration
    • Atmospheric pressure (760 mmHg) is referred to as 0 cm H2O
    • Negative pressure breathing: air moves into lungs as a result of airway pressure decreasing below atmospheric pressure
    • Positive pressure breathing: air moves into lungs as a result of atmospheric pressure exceeding airway pressure

    Passive Expansion of Alveoli

    • A pressure difference between the atmosphere and alveoli must be established to move air in/out of alveoli
    • During inspiration, alveoli expand passively in response to an increased transmural pressure difference
    • Increased volume, decreased pressure
    • During normal quiet expiration, the elastic recoil of the alveoli returns them to their original volume
    • Decreased volume, increased pressure

    Air Movement Into and Out of Lungs

    • Air moves into lungs when alveolar pressure is lower than atmospheric pressure
    • Increasing lung volume lowers airway pressure below atmospheric pressure, creating a pressure gradient that allows airflow into the lungs
    • Air moves out of lungs when alveolar pressure is sufficiently higher than atmospheric pressure
    • Decreasing lung volume increases airway pressure above atmospheric pressure, creating a pressure gradient that allows airflow out of the lungs

    Functional Residual Capacity (FRC)

    • Volume of gas in the lungs at the end of a normal tidal expiration, when no respiratory muscles are actively contracting
    • Occurs at the end of passive expiration
    • Determined by the balance of two forces: inward recoil of the lungs and outward recoil of the chest wall

    Intrapleural Pressure

    • Pressure within the pleural cavity
    • Normally negative (subatmospheric) at FRC (relaxation volume)
    • Lungs have a tendency to collapse due to inward elastic recoil of distended alveoli
    • Chest wall has a tendency to expand outward due to elastic recoil of flexible thorax
    • Negative IPP (-3 to -5 cm H2O) is caused by the mechanical interaction between lung and chest wall
    • At end-expiration, lung and chest are at an equilibrium of rest
    • At end-inspiration of a normal tidal volume, IPP becomes more negative (-8 cm H2O)

    Compliance of the Lung

    • Measure of the lung's distensibility
    • The ease with which lungs can be inflated
    • Compliance is volume-dependent: alveoli are more compliant at low volumes and less compliant at high volumes
    • Measured by the slope of the pressure-volume curve
    • It can be affected by diseases such as fibrosis and emphysema

    Types of Compliance

    • Static compliance: measured in the absence of gas flow
    • Dynamic compliance: measured in the presence of gas flow
    • Specific compliance: a measure of distensibility of lung as it relates to lung volume

    Clinical Evaluation of Lung Compliance

    • Specific compliance is used to denote compliance with respect to original lung volume
    • Compliance decreases with decreased lung volume; specific compliance does not
    • Standardizes for overall lung size/volume

    Elastance

    • Tendency to oppose stretch
    • Elastic recoil of alveolar walls increases at higher lung volumes
    • Increased elastance compresses alveolar gas, raising alveolar pressure above atmospheric pressure (exhalation)

    Elastic Recoil of Lungs

    • Due to elastic tissue and surface tension
    • Elastic tissue recoil: property of matter that causes it to return to its original position or configuration after having been displaced (stretched)
    • Surface tension: accounts for 2/3 of total elastic recoil forces in the normal lung
    • Surface tension forces occur at any gas-liquid interface
    • Generated by cohesive forces between water molecules and hydrogen bonding when unopposed at the surface of a liquid

    Surfactant

    • Surface active agent that decreases surface tension
    • Derived from type II alveolar epithelial cells (type II pneumocytes)
    • Major role is stabilizing alveoli by equalizing pressure inside smaller alveoli
    • Reduces surface tension recoil forces and the muscular efforts needed to ventilate
    • Aids in keeping the alveoli dry

    Atelectasis

    • Caused by respiratory changes during anesthesia
    • FRC decreases
    • Compliance decreases
    • Resistance increases
    • Develops in 90% of anesthetized lungs

    Interaction of Lung and Chest Wall

    • Inward elastic recoil of lung normally opposes the outward recoil of the chest wall
    • Chest wall recoil becomes inward at 70% TLC
    • FRC is the volume of gas in the lungs at the end of a normal tidal expiration, when no respiratory muscles are actively contracting

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    Description

    This quiz explores the concept of pressure difference generation and Boyle's Law, which states that pressure is inversely proportional to volume at a constant temperature. It covers the relationship between pressure and volume changes in a gas within a container.

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