• Definition: the energy used to overcome elastic recoil and airway resistance by the respiratory muscles for respiration (expressed in J/L)
• Elastic recoil
  • Increases with ↑ inspiratory volume
  • Influenced by, e.g., pulmonary airway elasticity and surface tension of alveoli
• Airway resistance
  • Increases with ↑ lung compression (e.g., due to ↑ intraabdominal pressure, pleural disease, mediastinal mass), ↑ flow rate (e.g., due to ↑ respiratory rate with increased turbulence), and ↓ airway diameter (e.g., due to bronchospasm)
  • Influenced by, e.g., tissue resistance (e.g., chest wall/lung resistance) and airway resistance
• Regulation
  • Optimization of respiratory rate (RR)
    • ↑ RR → ↓ elastic WOB
    • ↓ RR → ↓ resistive WOB
  • Optimization of tidal volume (VT)
    • ↑ VT → ↓ resistive WOB
    • ↓ VT → ↑ resistive WOB
• Changes in WOB due to respiratory condition
  • Restrictive diseases: ↑ RR and ↓ VT (to overcome elastic recoil)
  • Obstructive diseases: ↓ RR and ↑ VT (to overcome airway resistance)