Normal Aging of the Lung

This chapter focuses on the normal aging of lungs in various mammalian species such as mouse, rat, and dog. Various studies have demonstrated that lung aging in mice is associated with decreases in specific functional and structural parameters. These include increases in the phagocytic cell populations present in the lung airspaces, but decreased ability to engulf foreign particles. Decreases in antioxidant defense systems have also been noted in the lungs of aging mice. From a structural perspective, hyperinflation of the lungs and increases in interalveolar pore size and number are key features of the lung aging process in mice. The dynamics of lung growth, development, and aging in the rat is a continuous process that involves every tissue compartment of the lungs. Significant changes in aging adult rats are primarily within alveolar type II cells and the noncellular portions of the interstitium. Changes in cell number, size, and function associated with aging are likely to impact on lung physiology, metabolism, and immunity. Such changes could significantly alter the normal functions of the lung and its susceptibility to injury. Aging of canine lungs has many similarities to that seen in human lungs, but the aging process in dogs occurs over a shorter time frame than in humans. The accumulation of dust-laden macrophages as well as lumenal enlargement of alveolar ducts are hallmarks of this aging process. Changes in the relative velocity of mucus flow in the trachea with aging also parallels changes observed in the aging human trachea.