LUNG VOLUME

• Lung Compliance

  
• • Distensibility

  - capacity of a substance to be stretched
• • Compliance

  - degree of distensibility
• • Elastance

  - degree of stiffness
• Determinants:

  • Tissue elasticity - 1/3
  • Surface tension effect - ⅔
• • Surface tension

  Water molecules are attracted to each other. In a liquid, the attractive forces are experienced in every direction. However, at the surface there is an interface between water and air. Hence, there are no attractive forces above the surface to balance the attractive forces below, which creates an imbalance. The surface molecules experience force from the underlying molecules, which results in a tension at the surface.
• • Surfactant
  • 80-90% phospholipid
  • Major constituent: dipalmitoylphosphatidyl-choline (DPCC)
• • 4 proteins (10-15%)
  • SP-A = regulation of surfactant turn-over, formation of tubular myelin
  • SP-B = increases lateral stability of phospholipid layer
  • SP-C = spreading ability of surfactant
  • SP-D = primarily involved in immune defense.
• It mainly decreases the surface tension.
• 3 important roles:

  • It increases the compliance of the lung.
  • It increases the stability of the alveoli.
  • It reduces the tendency for alveolar edema.
• Lung Compliance

  
• • Tidal Volume (TV) = 500 mL
  • In older citizens, they have lower tidal volume due to the collagen deposition decreasing the flow of air.
  • In gender, males have higher tidal volume than females because the thoracic dimension of males are larger than females.
• • Inspiratory Reserve Volume (IRV) = 2000-3000 mL
  • Maximum volume of air that can be inhaled after a normal tidal volume inspiration.
• • Expiratory Reserve Volume (ERV) = 1000-1500 mL
  • Maximum volume of air that can be exhaled after a normal tidal expiration.
• • Residual Volume (RV) = 1200 mL
  • The volume of air that remains in the lungs after a maximal exhalation.
• Residual volume cannot be estimated using spirometry. However, it can be estimated using lung capacities.
• Lung capacity is the summation of volumes.
• • Vital Capacity (VC) = 3100-4800 mL
  • Maximum volume that can be exhaled after a maximum inhalation.
• • Inspiratory Capacity (IC) = 300-3500 mL
  • Maximum volume of air that can be inhaled after a normal tidal exhalation.
• • Functional Residual Capacity (FRC) = 2500-3000 mL
  • Volume of air remaining in the lungs after a tidal expiration.
• • Total Lung Capacity (TLC) = 4500-6000 mL
  • Total volume of air inside the lungs after a maximum inhalation.
• VC = TV + IRV + ERV
• IC = TV + IRV
• FRC = ERV + RV
• TLC = TV + IRV + ERV + RV
• MINUTE VENTILATION

  
• The normal respiratory rate is 12-20 breaths per minute.
• ALVEOLAR VENTILATION

  
• • 70% (TV - 500 mL)= respiratory zone
  • 30% (TV - 150 mL) = conducting zone (anatomic dead space)
  • Normal alveolar ventilation is 4-6 L/min