Dr. Robert Hyland, MD, FRCPC, Physician-in-Chief, St. Michael's Hospital, Professor of Medicine, University of Toronto, Toronto, ON.
Before considering the impact of chronic obstructive pulmonary disease (COPD) in the elderly, the normal physiological changes that take place in the lungs with aging should be reviewed1 (Table 1). In general terms, the lungs lose elastic recoil properties and alveolar surface area. This results in a mild decline in expiratory flow rates, and an increase in trapped air (residual volume) along with a decrease in resting arterial partial pressure of oxygen (PaO2). Airway closure occurs progressively in dependent portions of the lung in the supine position beginning in the mid-40s, and the sitting position in the mid-60s. This airway obstruction results in some shunting and further hypoxemia. Muscle strength--particularly diaphragmatic--declines and the chest wall becomes stiffer, contributing to decreased exercise tolerance. Neural reflexes to hypoxia and hypercapnia as well as the perception of changes in lung stiffness and air flow obstruction are blunted in elderly patients, decreasing their awareness of acute problems. Despite all these changes, it is probably fair to say that lung aging is not limiting unless affected by disease. However, elderly patients also have a less effective cough, are prone to aspiration and have less effective lung defenses, thereby increasing the risk of infection.