The fastest growing segment of the U.S. population consists of individuals of age 65 and older. In the 2018 census, this segment comprised 52 million individuals or 16% of the population. Since the 1950s, the median age of the U.S. population has increased by 20 years.
The largest decrements in age-adjusted death rates have been occurring in older patients. With the increasing longevity of human population, it is necessary to understand the effects of aging on the respiratory system in healthy people. Perhaps, more importantly, because the age-related decrements in respiratory system function can be unmasked by disease, it is critically important to point out that the aged: (1) have an enhanced predisposition to lung disease; (2) have a decreasing reserve of respiratory system function that decreases their ability to cope with the stresses of illness, injury, and surgery; and (3) may have differing responses to therapy when compared with their younger counterparts.
Even in individuals who enjoy apparently good health, there are measurable decrements in function of the respiratory system with age. These changes occur progressively as a healthy individual grows older and are most marked beyond 60 years of age. Cross-sectional studies show clear differences between elderly and young persons with regard to the structure and function of the components of the respiratory system (Table 18-1). As we will see, however, caution must be exercised in ascribing observed changes to age alone. It is also necessary to be aware that longitudinal studies of “healthy” individuals followed to old age are essentially not available. Where appropriate, methodologic problems in the available cross-sectional studies are described.
TABLE 18-1Respiratory System: Functional Divisions and Changes with Aging ||Download (.pdf) TABLE 18-1 Respiratory System: Functional Divisions and Changes with Aging
|Functional Division ||Components ||Function ||Change(s) with Aging |
|Conducting airways ||All airways not involved in gas exchange (mouth to terminal bronchioles) ||Gas movement between environment and alveolar space ||Slight changes in size; calcification; glandular hypertrophy |
|Lung parenchyma ||Gas-exchanging airways and vessels; connective tissue framework ||Gas exchange between alveolar space and capillary blood ||Enlarged terminal airspaces; ventilation/perfusion mismatching |
|Bellows apparatus ||Chest wall and muscles of respiration ||Provide mechanical forces for ventilation ||Increased rigidity of chest wall; decreased respiratory muscle strength |
|Ventilatory control ||Respiratory control center (pons and medulla); carotid and aortic bodies ||Maintaining homeostasis by altering ventilation to match metabolic needs ||Markedly decreased responses to hypercapnia and hypoxemia |
|Cardiovascular system ||Heart and systemic vasculature ||Blood transport and tissue exchange of respiratory gases ||Decreased maximal heart rate and cardiac output; decreased responsiveness to hypoxemia |
Although age-associated changes can be measured easily by objective testing, it is important to note that the routine activities of healthy elderly persons are not limited by the decreasing respiratory system function. However, whereas youthful persons have a marked excess of functional capacity over the amount required to meet metabolic needs ...