This chapter first reviews the changes in lung function with aging that are known to occur in healthy persons (normal, never smokers). Included are the major categories of pulmonary function tests: static lung volumes, maximal expiratory flow, lung mechanics, and gas exchange, plus bronchodilator (BD) response and nonspecific airway reactivity. Table 82-1 summarizes these changes. The chapter then adds a discussion of how lung function tests maybe used by a clinician to assist in the differential diagnosis of asthma and chronic obstructive pulmonary disease (COPD) in an elderly patient, and to objectively measure the efficacy of asthma and COPD therapy (see Chapter 83 for additional information on this topic).
Table 82-1 Effects of Aging on Lung Function ||Download (.pdf)
Table 82-1 Effects of Aging on Lung Function
Lower maximal expiratory flows: FEV1, FEV1/FVC, FEF 75%
Increased FRC and RV, lower VC, but stable TLC
Lower diffusing capacity (oxygen uptake)
Lower PO2 and SpO2 as a consequence of V/Q mismatch (but no change in PCO2)
Lower respiratory muscle strength and endurance
Stiffer chest wall (less compliant)
Increased lung tissue compliance (loss of lung recoil)
Reduced respiratory drive (for hypoxia, hypercarbia, and resistive loads)
Increased airway reactivity (but no change in bronchodilator responsiveness)
Total lung capacity (TLC) is the volume of air within the respiratory system when a subject makes a maximal voluntary inspiratory effort (and the air seen in the lungs on a chest x-ray). It is determined by the balance of forces between the maximally activated inspiratory muscles and the elastic recoil of the lung and chest wall. A decrease in TLC and other static lung volumes is called restriction.
The elastic recoil of lung tissue decreases with aging (just as the skin becomes less elastic), making the lungs easier to expand during a deep breath toward TLC. This reduction of elastic recoil tends to increase TLC; however, the chest wall (rib cage) becomes stiffer with aging, so that a maximal inspiratory effort is not able to achieve a higher lung volume even though the lungs themselves have become easier to expand. Thus, TLC normally remains stable throughout the aging process.
The volume of air remaining in the lungs when subjects have exhaled as much air as possible is called residual volume (RV). Because lung elastic recoil decreases as a consequence of normal aging, the RV and RV/TLC increase from young adulthood to older age. An abnormally high RV/TLC is called hyperinflation, can often be seen on a chest x-ray, and occurs with ...