What happens to lung compliance in older adults with advancing age?

Lung Compliance Changes with Age

Lung compliance increases with age due to loss of elastic recoil, while chest wall compliance decreases, resulting in a net increase in functional residual capacity and residual volume. 1

Structural Changes Driving Compliance Alterations

Lung Parenchymal Changes

• Elastic recoil of the lung progressively decreases with aging, leading to what is termed "senile emphysema"—a condition characterized by reduced alveolar surface area without true alveolar destruction. 2, 3
• This loss of elastic tissue causes increased static lung compliance, meaning the lungs become more distensible and require less pressure to inflate. 2
• The alveolar-capillary diffusing capacity decreases as a consequence of reduced surface area for gas exchange. 2

Chest Wall Changes

• Chest wall compliance decreases significantly with advancing age due to calcification of costovertebral and costochondral articulations, development of dorsal kyphosis, and "barrel chest" deformity. 2, 3
• Quantitatively, thoracic wall compliance drops from approximately 350 ml/cmH₂O in young adults (20-29 years) to 136 ml/cmH₂O in those aged 60-69 years, and 210 ml/cmH₂O in those aged 70-79 years. 4
• This stiffening of the chest wall increases the work of breathing in older adults. 3

Functional Consequences

Lung Volume Changes

• The combination of increased lung compliance and decreased chest wall compliance causes functional residual capacity (FRC) to increase with age. 2, 5
• Residual volume (RV) increases progressively due to loss of elastic recoil in airways and alveoli combined with weakened expiratory muscles, leading to premature airway closure during expiration. 2, 5
• Vital capacity decreases as residual volume encroaches on total lung capacity. 2, 5
• Closing volume increases, resulting in greater ventilation/perfusion mismatch, particularly when supine. 1

Expiratory Flow Limitations

• Maximal expiratory flow rates decline due to the combined effects of reduced elastic recoil (which normally provides the driving pressure for expiration) and decreased respiratory muscle strength. 2
• FEV₁ declines at approximately 29 ml/year in nonsmokers, though this rate may accelerate in older individuals. 1
• The flow-volume curve becomes more convex to the volume axis at low lung volumes. 5

Clinical Pitfalls and Considerations

Diagnostic Challenges

• The natural decline in FEV₁/FVC ratio with age can lead to overdiagnosis of COPD if clinicians rely solely on this ratio without confirming that FEV₁ is less than 80% predicted. 6
• Age-related physiological changes must be distinguished from pathological processes when interpreting pulmonary function tests. 1

Vulnerability to Respiratory Failure

• Older adults have diminished ventilatory responses to hypoxia and hypercapnia, making them more susceptible to ventilatory failure during high-demand states such as pneumonia or heart failure. 6, 3
• Despite these structural changes, the respiratory system maintains adequate gas exchange at rest and during exercise throughout the lifespan, with PaCO₂ remaining normal and PaO₂ declining only modestly (-0.3 mmHg per year), with this decline attenuating after age 70. 2

Respiratory Muscle Function

• Respiratory muscle strength decreases with age, correlating with cardiac index, nutritional status, and degree of hyperinflation. 2
• This weakness impairs effective cough and airway clearance, increasing vulnerability to respiratory infections. 3

Rate of Physiological Decline

• All organ systems decline at approximately 1% function per year after age 40, with lung function following this pattern. 1
• The decline is more pronounced in individuals with smoking history or occupational exposures. 1