The majority of pulmonary disease processes observed in young patients are also observed in elderly populations. However, older people have numerous physiologic changes associated with aging that alter their response to these disease processes when compared to younger patients. Furthermore, they frequently have associated comorbidities that can complicate the management of respiratory conditions. This chapter will review aging physiology and the most commonly encountered pulmonary conditions.
Physiologic changes with aging
Numerous changes to the respiratory system occur naturally with aging. First, the chest wall stiffens. This is likely due to degenerative joint disease of the spine, kyphoscoliosis, and calcifications of the costal cartilages and chondrosternal junctions. These changes lead to almost a one-third decrease in chest wall compliance. With age, airway size decreases as elastic tissue is replaced by collagen. Small airways collapse as end inspiration increases, leading to a greater amount of air trapping. The diaphragm becomes less efficient as well, resulting in increased work of breathing.
The alveolar-arterial oxygen difference increases in older persons due to a variety of factors, including loss of alveolar surface area and an increase in ventilation-perfusion mismatch. Despite these changes, elderly patients should not be hypoxic at sea level in the absence of disease. They also should not have a significant increase in alveolar hypoventilation resulting in elevations of arterial pCO2. Either of these findings should prompt investigation into an underlying disease process.
Finally, geriatric patients can undergo a number of physiologic changes that decrease their natural mechanical defenses. The cough reflex is decreased as well as mucociliary clearance. Elderly patients can also be susceptible to dysfunction of the swallowing mechanism from central nervous system disorders, primary swallowing dysfunction, or sedating medications, thus increasing the frequency of aspiration events.
Obstructive lung diseases
Obstructive lung diseases, including chronic obstructive pulmonary disease (COPD) and asthma, are diseases frequently encountered in the geriatric population. Approximately 11.6% of the US population 65 or older suffers from COPD. Although fully reversible asthma may be seen in elderly patients, it is less likely to be reversible in this population due to a diminished response to β-agonists with aging. Therefore, this discussion will focus on COPD, as this is the more common geriatric entity.
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