Describe the effects of ageing on the respiratory system.

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College Answer

Answers should have included the effects of ageing on the efficiency of gas exchange, how the expected PaO2 changes with age, and its causation. Anatomical changes should have been included as should changes in lung volumes, particularly the significance of an increased closing volume. Marks were not awarded for the effects of disease states.

Discussion

When designing the answer for a CICM SAQ, one typically asks oneself, "why would I not present this as a table?" For this SAQ, that question has no good answer. Thus:

Age-related Changes in the Respiratory System, 
and their Various Effects
Age-related changes Effect of these changes

Airway function and structure

  • Increased airway reactivity
  • Decreased ciliary number and activity
  • Higher risk of bronchospasm
  • Bronchospasm requires a lesser stimulus
  • Clearance of secretions is impaired

Structural properties of the chest wall:

  • Calcification of costal ligaments
  • Thoracic vertebral height loss
  • Kyphosis
  • Decreased chest wall compliance
  • Higher residual volume (RV)
  • Higher FRC
  • Lower vital capacity (VC)
  • Unchanged total lung capacity (TLC)

Function of respiratory muscles:

  • Decreased total muscle mass
  • Decreased muscle strength
  • Decreased proportion of fast-twitch fibres
  • Decreased MIP (maximum inspiratory pressure)
  • Decreased FEV1
  • Decreased maximum minute ventilation
  • Fatigue develops more rapidly
  • Exercise capacity is decreased

Structure of the lungs

  • "Senile emphysema"- hyperinflation
  • Degeneration of elastic fibres
  • Reduction in supporting tissue around small airways
  • Increased lung compliance
  • Decreased elastic recoil
  • Decreased diaphragmatic excursion
  • Increased dead space ventilation
  • Increased closing volume due to premature small airway closure, increasing the risk of gas trapping

Gas exchange

  • Increased alveolar–capillary membrane thickness
  • Decline in DLCO

Control of ventilation

  • Decrease in efferent neural output to respiratory muscles
  • 50% reduction in response to hypoxia
  • 40% reduction in response to hypercarbia

Immunological changes

  • Increased immunoglobulin content
  • Decreased alveolar macrophage population
  • Increased susceptibility to bronchospasm
  • Increased susceptibility to infection
  • Slower recovery from infection

References

References

Sharma, Gulshan, and James Goodwin. "Effect of aging on respiratory system physiology and immunology." Clinical interventions in aging 1.3 (2006): 253.