Compliance Definition etc

• Compliance - Definition:

  • Compliance refers to the distensibility (stretchiness) of an elastic structure
  • The change in pulmonary volume per unit pressure change
  • In health respiratory system highly compliant and needs little pressure to change volume on inspiration
  • Lungs most compliant above Functional Residual Capacity (FRC is the amount of air left in the lungs after normal expiration)
  • For effective inspiration to occur BOTH the lungs and chest wall must be compliant
• Compliance Curve

  
• • The distensibility of the lungs is called lung compliance
  • The distensibility of the chest wall is called chest wall compliance
• Chest wall compliance + Lung compliance = Total Lung Compliance
• • To maintain efficient inspiration, total lung compliance must be optimal
  • Any pathology which reduces the compliance of EITHER the chest wall OR the lung will reduce total lung compliance and make inspiration more difficult
  • Reduced total lung compliance leads to limited or reduced inspiration
• Consequences of Reduced Compliance:

  1. Reduced total lung compliance ->
  2. Increase in respiratory load and Increase in work of breathing / O2 consumption ->
  3. Respiratory muscle fatigue ->
  4. Inadequate alveolar ventilation ->
  5. Respiratory failure ->
• Respiratory disease characterised by reduced total lung compliance is classified as Restrictive lung disease