Changes in functional imaging with aging

From birth to maturity, body weight may increase from 15 to 40-fold. However, changes do not cease once adult size has been attained. There is a continual process of physiological and biochemical progression that becomes apparent in what the authors view as ''aging.'' Although early developmental changes are pronounced and have been studied in the area of ''pediatric nuclear medicine,'' there are also major alterations that occur in later years. These have been less well documented by the procedures of nuclear medicine. The present analytic review covers a limited number of organ systems, from early adulthood through the later stages of life. At the National Institutes of Health it has been estimated that the most rapidly growing population segment in the United States (in terms of percentages) consists of those 85 years of age and older. These individuals have ben referred to as the ''oldest old.'' When possible, the authors refer to studies on these oldest old, but they recognize that few definitive works have appeared in the nuclear medicine literature concerning those individuals. Even among those who have not attained this age, age-related or age-describable alterations are having a major impact on delivery of medical care. For example, among patients undergoing femoropopliteal bypass surgery, the mean length of stay in hospital is related to the patient's age (increasing at a rate of 1% per year)