Physiologic Changes in the Aging Lung

Abstract

Aerobic cellular metabolism, a fundamental requisite for homeostasis, is dependent on oxygen delivery (O2D) and acid–base status. These, in turn, require a ventilatory response that couples gas exchange at the lung with metabolism at the cellular level. Senescence-based mechanisms adversely affect the ventilatory response, however, through reductions in respiratory physiology, termed normal aging, and through increases in the prevalence of cardiopulmonary disease, termed usual aging. Both forms of aging can lead to impairments in central respiratory drive, respiratory muscle strength, respiratory mechanics, and lung perfusion, yielding various forms of alveolar hypoventilation and the mismatch of ventilation with (lung) perfusion. Clinically, these impairments increase the risk of exercise intolerance and respiratory failure, including disturbances in O2D and acid–base status. Those at highest risk are older persons with cardiopulmonary disease, particularly if they are also obese, report the use of respiratory suppressants, or are in the midst of an episode of acute lung injury such as pneumonia. This chapter reviews the adverse effects of normal aging on respiratory physiology, at rest and with exercise. It also includes an illustrative case presentation and a discussion regarding the clinical implications of age-related reductions in respiratory physiology, relative to cardiopulmonary disease, obesity, respiratory suppressants, and acute lung injury.