The Aging lung

Despite a reduction in lung function, the disease-free aged respiratory system still has excellent capacity to allow individuals to maintain high levels of activity and exercise in those able to do so. The major factor in declining lung function is loss of lung elasticity, aggravated by stiffening of the chest wall and reduced respiratory muscle strength. This results in airspace dilatation, increased collapsibility of small airways, and a reduction in expiratory volumes, all of which are consistent with emphysema or small airways disease. Gas exchange is good at rest, even if there is an increased ventilation-perfusion mismatch during exercise, due to small airway closure and reduced alveolar surface area. The loss of lung elasticity may be due to stretch, or alteration in cross-linkage, of elastin and/or collagen, although their total concentrations in the lung are relatively constant with age, suggesting that a remodelling process occurs. The causes underlying the changes in structure and function in the human lung may be multifactorial, including glycosylation of collagen, oxidative stress and protease-antiprotease imbalance. There is limited evidence, however, to suggest that there may be low-grade inflammation in the aged lung, including increased absolute neutrophil numbers and elevated concentrations of relevant cytokines in lung secretions. Whether this is responsible for the pathological similarities between the aging lung and emphysema remains to be determined. The physiological loss of adaptability with increasing age makes the older person much more susceptible to the detrimental effects of pulmonary infections and chronic lung diseases. However, whether this can be modified remains to be determined. © 2007 Cambridge University Press.