Updated: 3/25/2019

Lung Volumes and Capacities

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                           Lung Volumes

Lung Volumes
  • Lung volumes are measured by spirometry
  • Tidal Volume (TV)
    • normal, quiet breathing involves inspiration and expiration of TV
    • TV ~ 500 mL
  • Inspiratory Reserve Volume (IRV)
    • additional volume of gas that can be inspired above TV on maximal inspiration
    • IRV ~ 3,000 mL
  • Expiratory Reserve Volume (ERV)
    • additional volume of gas that can be expired below TV on maximal expiration
    • ERV ~ 1,200 mL
  • Residual Volume (RV)
    • volume of gas that remains in lungs following maximal expiration
    • RV ~ 1,200 mL
    • cannot be measured by spirometry
Lung Capacities
  • a lung capacity includes ≥ 2 lung volumes
  • Inspiratory Capacity (IC)
    • TV + IRV
    • IC ~ 3,500 mL
  • Functional Residual Capacity (FRC) 
    • ERV + RV
    • volume of gas that remains in lungs following normal TV expiration
    • equilibrium volume of lungs
    • FRC ~ 2,400 mL
  • Vital Capacity (VC)
    • IC + ERV = TV + IRV + ERV
    • volume of gas that can be expired following maximal inspiration
    • VC ~ 4,700 mL
  • Total Lung Capacity (TLC)
    • VC + RV = TV + IRV + ERV + RV
    • TLC ~ 5,900 mL
Pulmonary Vascular Resistance
  • Lowest at FRC
    • higher at volumes greater and less than FRC
  • Contributions from both the intraalveolar vessels (bigger influence) and extraalveolar vessels
  • Increased by
    • inhalation
      • increased pressure on intra-alveolar vessels by expanding alveoli
    • forced exhalation
      • increased intrathoracic pressure compresses pulmonary vessels
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