Mechanics of Ventilation

VENTILATION
1. Caused by pressure-Volume relationship
2. Boyle's Law
  1. P~1/V
  2. Pressure of gas in inversely proportional to volume causing inspiration
  3. Decreased in lung volume raises intrapulmonary pressure causing expiration
3. Air moved from higher pressure to low pressure
INTRAPULMONARY & INTRAPLEURAL PRESSURE
1. At Rest
  1. Atmospheric pressure
    1. 760 mmHg
  2. Alveolar Pressure
    1. 760mmHg
2. Inspiration
  1. Atmospheric Pressure
    1. 760
  2. Alveolar Pressure
    1. 757
  3. Atmospheric pressure is greater than alveolar pressure therefore air will go IN
3. Expiration
  1. Atmospheric pressure
    1. 760
  2. Alveolar Pressure
    1. 763
  3. Atmospheric pressure is less than alveolar pressure therefore air will go OUT
ALVEOLAR PRESSURE DROPS
1. Diaphragm contracts
  1. Which Increases VOLUME
    1. Decreases Pressure
      1. Air comes
PNEUMOTHORAX
1. Collapsed Lung
  1. Airs enters into the intrapleural space through comm. from chest wall
    1. Occurs because alveolar pressure is normally greater than the pleural cavity pressure
      1. As air escapes from the lung, it recoils and will begin to collapse
      2. Because air comes inside pressure increases
PROPERTIES OF LUNGS
1. Ventilation of the lung requires:
  1. Compliance
    1. Ability to strecth under pressure (inspiration)
      1. Lung volume: transmural pressure V/P
        Reduced by factors that cause resistance to distension
    2. High Compliance
      1. Stretches Easily
        Facillitates lung expansion
    3. Low Compliance
      1. Requires more force
        Restrictive lung disease
        Fibrotic lung disease
        Inadequate surfactant production
  2. Easticity
    1. Returning to initial size after stretch (expiration)
      1. Elastic recoil after inspiration
        Tension increases during inspiration & is reduced recoil during expiration
  3. Surface Tension
    1. Promotes alveolar collapse & resist distension
      1. Lung secrete & absorb ions and water
    2. Absorption
      1. Osmosis driven by Na+ active transport INWARD across alveolar endothelium
    3. Secretion
      1. Osmosis driven by active transport of Cl- OUTWARD
    4. Surface Tension
      1. H2O molecules are attached to other H20 molecules with increase alveolar pressure
SURFACTANT
1. Production begins in fetal life
  1. Phospholipid DPPC proteins
    1. Type II alveolar cells of lung into single alveolus
      1. More concentrated in small alveolus
      2. Increases pulmonary Compliance
        Without surfactant, small alveoli collapse into larger alveoli (reducing compliance
2. Respiratory distress syndrome
  1. <34 WEEKS
    1. Have trouble inflating lungs
3. Acute Respiratory Distress Syndrome
  1. Sepsis bacterial infection
  2. Decreased compliance & surface secretion
    1. impaired gas exchange
      1. Death due to muti-organ failure
4. is also impaired with Emphysema & Pulmonary fibrosis

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Mechanics of Ventilation

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