Keith C. Meyer
The human lung reaches the zenith of its functional capacity in the late second to the third decade of life, but age-associated changes in lung structure and function gradually ensue once this zenith has been reached. Although there is considerable interindividual variation, age-associated decline in lung function of healthy, nonsmoking individuals becomes apparent in the fifth to sixth decade of life when physiologic testing is performed. This decline in lung function coincides with morphologic changes that are associated with alterations in structural proteins that comprise lung matrix, and appears to be caused largely by decreased lung elastic recoil. Other age-related factors associated with declining lung function include diminished chest wall compliance, blunting of ventilatory responses, a decline in respiratory muscle strength, a decline in arterial oxygen tension, an increased prevalence of sleep-disordered breathing, and diminished exercise capacity. Despite these changes, nonsmoking, healthy elderly individuals do not tend to develop clinical symptoms as a consequence of declining lung function. However, certain lung disorders such as chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF) tend to make their appearance in elderly persons and cause significant respiratory system dysfunction, and the elderly display an increased susceptibility to respiratory infection. Animal models have provided some insights into age-associated decline in lung function in humans, but the precise causes of age-associated changes in lung function remain obscure.
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