Pulmonary Changes with Aging

Pulmonary Elasticity

• Aging lungs develop decreased elastic recoil and increased compliance due to changes in the lung parenchyma. Loss of elastic recoil causes¹:
  • Small airway collapse: elasticity and natural recoil are needed to hold small airways open during changes in lung volumes during respiration. Airflow becomes limited during expiration due to the collapse of intrathoracic airways. Small airway collapse also is one of the causes of ↑ residual volume (RV).
  • Decreased alveolar surface area: loss of alveolar walls results in small alveoli coalescing to form larger sacs.
• Closing capacity (CC) increases with age until it surpasses functional residual capacity (FRC), meaning that airway obstruction may occur during normal tidal breathing.²
  • CC is the lung volume at which small airway closure begins
  • CC = FRC in the supine position at ~44 years old.
  • CC = FRC in the upright position at ~66 years old
  • Mnemonic for factors that increase closing capacity – ACLS-S. Age, Chronic bronchitis, LV failure, Smoking, Surgery
• The overall effect of these changes in elasticity is increased ventilation-perfusion (V/Q) mismatching.²
• Consequently, PaO₂ decreases with age.
  Estimated PaO₂ values for healthy adults is calculated with: PaO₂ = 110-(Age*0.4)
• Memory aid: The pulmonary changes associated with aging are often described as “senile emphysema” due to its similarity with the pathologic condition.

Chest Wall Rigidity & Muscle Weakness

• Calcification and kyphosis of the thoracic spine, osteoporosis, arthritis of the costovertebral joints, and structural changes to the intercostal muscles all contribute to increased chest wall rigidity.¹
• Loss of elastic recoil causes an enlargement (barrel shape) of the thorax, which pulls the diaphragm flatter. This change causes the diaphragm to be less efficient, requiring increased work of breathing and results in a decreased transdiaphragmatic pressure gradient.³
• Loss of muscle strength, particularly in accessory respiratory muscles, results in decreased maximal breathing capacity in response to stress and decreased cough, which may lead to diaphragm fatigue during higher ventilatory demand.³

Spirometry Changes

• Total lung capacity (TLC) correlates with height, which decreases with age. However, the changes in other lung volumes that make up TLC balance so that there is no net change in TLC.²
• Residual volume (RV): decreased alveolar surface area and small airway collapse due to loss of elastic recoil results in increased RV.^1,2
• Vital capacity (VC): the increase in RV causes a compensatory decrease in VC.¹
• FRC: determined by the balance between the inward elastic recoil of the lungs and the outward recoil of the chest wall. Increases by 1-3% per decade due to a more rapid decrease in lung recoil than increase in chest wall rigidity.¹