Normative aging of the respiratory system.

An absolute quantified normal rate of change and normal range of functions of the respiratory system applicable to all older adults as they age is elusive. Like life expectancy, which is dependent on a cohort effect, the norms of respiratory system function are related to the birth cohort to which a given individual belongs and the age at which the parameter is assessed. No single rate of change can express normal across all age ranges even for those individuals in apparently good health [29]. Analogous to defining risk factors for a disease, determining that a change in anatomy or physiology is not disease requires stringent prospective evaluation for the absence of occult disease and known risk factors for disease prior to concluding that the alteration is inevitable with the normal aging process [19,31]. Additional limitations in quantifying the norms of respiratory function with age are the lack of participation of the oldest adults in studies and the lack of precision and accuracy in these performance-based measurements. The data, although limited, do support a qualitative emphysematous change in lung histology and lung-thorax mechanics. This change plus altered lung volumes influence oxygenation and oxygen consumption. There is no evidence that the changes in the respiratory system with aging impact day-to-day function of older adults, but they may become evident under circumstances when physiologic demand reaches the limits of supply. Despite changes in cholinergic and adrenergic receptor functioning, there is no evidence to suggest altering prescribing these classes of medications for older people. Pioneer physiologists asked the original question "Is there a difference in this measurement for older people?" Researchers in pulmonary medicine, pathology, radiology, epidemiology, and public health have continued to revise the question toward the clinical implications while studying the aging process from their respective viewpoints. Clinicians who need to develop an integrated care plan should neither rely on formulas to "normalize" a measurement for age nor assume that a established predictive value of a diagnostic test done in young adults can be automatically applied to geriatric patients [4]. Rather, the clinical situation should consider that the variability in normal is greater with older age and that all diagnostic tests and care plans should be considered in the context of the patient's symptoms [5].