The worldwide aging population is rapidly increasing and Korea also expects to become an ultra-aging society as elderly individuals aged 65 years or older will comprise more than 25 % of its total population by 2025. 1 The human body undergoes a variety of aging-related changes including changes in the respiratory system. However, normal variations of such changes may not be easily distinguishable from pathological changes because of marked interindividual differences. 2 Changes in the

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... ry system with aging do not cause serious problems such as airway obstruction or parenchymal lung disease in healthy people because they have reserve lung capacity. However, when the affected person has comorbid underlying lung disease due to previous infections or smoking, the reserve is reduced, and therefore, lung problems can arise more easily. The changes in the respiratory system caused by aging generally include structural changes in the thoracic cage and lung paren-Changes in the respiratory system caused by aging generally include structural changes in the thoracic cage and lung parenchyma, abnormal findings on lung function tests, ventilation and gas exchange abnormalities, decreased exercise capacity, and reduced respiratory muscle strength. Decreased respiratory system compliance caused by reduced elastic recoil of the lung parenchymaand thoracic cage is related to decreased energy expenditure by the respiratory system. Lung function, as measured by 1-second forced expiratory volume and forced vital capacity (FVC), decreases with age, whereas total lung capacity remains unchanged. FVC decreases because of increased residual volume and diffusion capacity also decreases. Increased physiological dead space and ventilation/perfusion imbalance may reduce blood oxygen levels and increase the alveolar-arterial oxygen difference. More than 20% decrease in diaphragmstrength is thought to beassociated withaging-related muscle atrophy. Ventilation per minute remains unchanged, and blood carbon dioxide concentration does not increase with aging. However, responses to hypoxia and hypercapnia are decreased. Exercise capacity also decreases, and maximum oxygen consumption decreases by >1%/year. Consequence of these changes, many respiratory diseases occur with aging. Thus, it is important to recognize these aging-related respiratory system changes.