Age-Related Changes in the Respiratory System
Ageing affects every component of the respiratory system, gradually altering the way the lungs expand, how efficiently they participate in gas exchange, and how well they defend themselves against infection. These changes occur slowly over decades, often going unnoticed until a period of illness or increased metabolic demand makes them more apparent.
Although older adults may maintain reasonable respiratory function at rest, age-related structural and physiological changes reduce respiratory reserve, making them more vulnerable to respiratory complications, medication effects, and environmental stressors. Understanding these changes helps explain why respiratory illness tends to be more severe in older adults and why early intervention is often critical.
What You Need to Know
Ageing is associated with gradual changes in both lung structure and function. Elastic recoil decreases over time, leading to larger, less uniformly shaped alveoli and a reduction in effective surface area for gas exchange. This contributes to an increase in physiological dead space. At the same time, the chest wall becomes stiffer due to calcification of costal cartilages, spinal changes, and reduced intercostal muscle strength. As a result, the lungs are harder to expand, and breathing becomes more reliant on diaphragmatic effort to maintain adequate ventilation.
Key changes with ageing include:
Reduced elastic recoil → larger, less efficient alveoli
Increased chest wall stiffness → greater work of breathing
Respiratory muscle weakness → reduced ability to take deep breaths
Impaired cough and clearance → increased infection risk
Ventilation–perfusion mismatch → mild decline in oxygenation
Respiratory muscle strength and endurance also decline, limiting the ability to generate forceful breaths or respond to increased respiratory demand. This makes older adults more susceptible to fatigue during illness. In addition, a weakened cough reflex and reduced mucociliary clearance impair the ability to clear secretions, significantly increasing the risk of pneumonia.
Gas exchange becomes less efficient with age. The pulmonary capillary network becomes less dense, reducing perfusion in some areas of the lung. This contributes to less precise matching of ventilation and perfusion, resulting in a mild but measurable decline in arterial oxygen levels, even in otherwise healthy individuals.
Beyond the Basics
Ageing and Respiratory Control
Ageing alters the regulation of breathing at both central and peripheral levels. The sensitivity of central chemoreceptors to carbon dioxide and peripheral chemoreceptors to hypoxia declines with age. As a result, older adults may show a delayed or blunted increase in respiratory rate and tidal volume in response to rising carbon dioxide or falling oxygen levels. This reduced ventilatory drive can mask early physiological deterioration and delay recognition of hypoventilation, particularly during acute illness, sedation, or opioid exposure.
Protective airway reflexes also become less effective. The cough reflex weakens, and coordination between breathing and swallowing may deteriorate, increasing the risk of aspiration. These changes further compromise airway protection and contribute to secretion retention within the lower respiratory tract.
Age-Related Changes in Respiratory Immune Defence
The immune defences of the respiratory system progressively decline with age. Ciliary activity slows, impairing mucociliary clearance and reducing the efficiency with which inhaled particles and pathogens are removed. Airway mucus becomes thicker and more difficult to mobilise, further limiting clearance.
At the alveolar level, both the number and functional capacity of macrophages decrease, reducing effective phagocytosis and pathogen elimination. In addition, secretory IgA levels in the airway mucosa fall, weakening the first line of immune defence. Collectively, these changes increase susceptibility to respiratory infections such as influenza, pneumonia, and bronchitis, and contribute to more severe or prolonged disease courses.
Reduced Respiratory Reserve in Older Adults
The combined effects of structural, neuromuscular, and immunological ageing result in a marked reduction in respiratory reserve. Loss of lung elasticity, decreased chest wall compliance, weakened respiratory muscles, impaired ventilatory reflexes, and diminished immune function limit the capacity of the respiratory system to respond to physiological stress.
Consequently, conditions that cause mild respiratory compromise in younger adults, such as viral infections, mild heart failure, or brief periods of immobility, may precipitate significant breathlessness, hypoxaemia, atelectasis, or respiratory failure in older adults. This reduced reserve underscores the importance of early recognition of subtle respiratory changes and an appreciation of age-related vulnerability when assessing respiratory function.
Clinical Connections
Understanding age-related changes in respiratory function helps clinicians anticipate complications and tailor care. Older adults desaturate more quickly during illness or immobility due to reduced functional residual capacity and diminished oxygen reserves. They are also more susceptible to respiratory depression from opioids, sedatives, and anaesthetic agents, as respiratory muscle strength declines and chemoreceptor responsiveness becomes blunted.
Key clinical implications include:
Faster desaturation during illness or immobilisation
Increased sensitivity to sedatives and opioids → risk of respiratory depression
Higher risk of postoperative complications → atelectasis, aspiration, secretion retention
Reduced airway clearance → increased pneumonia risk
Lower respiratory reserve → greater impact of chronic lung disease
Older patients are at increased risk of postoperative pulmonary complications, including atelectasis, aspiration pneumonia, and difficulty clearing secretions. Preventative strategies such as early mobilisation, respiratory physiotherapy, incentive spirometry, and careful medication management are particularly important in this population.
These physiological changes also explain why chronic respiratory diseases such as COPD become more debilitating with age, as the natural decline in respiratory reserve amplifies underlying pathology. Even in the absence of chronic lung disease, older adults commonly experience breathlessness on exertion, reflecting the reduced efficiency of the ageing respiratory system.
Test Yourself
Why does arterial oxygen saturation decline gradually with age?
How does reduced elastic recoil affect breathing mechanics in older adults?
Why are older adults more prone to respiratory infections?
How does ageing influence the response to hypoxia and hypercapnia?
Why are postoperative pulmonary complications more common in older adults?