R E V I E W Effect of aging on respirator y system physiolog y and immunolog y Gulshan Sharma1 James Goodwin2 1Division of Allergy, Pulmonary, Immunology, Critical Care, and Sleep (APICS), Department of Internal Medicine, University of Texas Medical Branch, Galveston, TX, USA; 2Division of Geriatrics, Department of Medicine, University of Texas Medical Branch, Galveston, TX, USA Correspondence: Gulshan Sharma Division of Allergy, Pulmonary, Immunology, Critical care, and Sleep (APICS), Department of Internal Medicine,The University of Texas Medical Branch, 301 University Blvd, Galveston,TX 77555-0561, USA Tel +1 409 772 2436 Fax +1 409 772 9532 Email gulshan.sharma@utmb.edu Abstract: With the looming expansion of the elderly population of the US, a thorough understanding of “normal” aging-related changes on the respiratory system is paramount. The respiratory system undergoes various anatomical, physiological and immunological changes with age. The structural changes include chest wall and thoracic spine deformities which impairs the total respiratory system compliance leading to increase work of breathing. The lung parenchyma loses its supporting structure causing dilation of air spaces: “senile emphysema”. Respiratory muscle strength decreases with age and can impair effective cough, which is important for airway clearance. The lung matures by age 20–25 years, and thereafter aging is associated with progressive decline in lung function. The alveolar dead space increases with age, affecting arterial oxygen without impairing the carbon dioxide elimination. The airways receptors undergo functional changes with age and are less likely to respond to drugs used in younger counterparts to treat the same disorders. Older adults have decreased sensation of dyspnea and diminished ventilatory response to hypoxia and hypercapnia, making them more vulnerable to ventilatory failure during high demand states (ie, heart failure, pneumonia, etc) and possible poor outcomes. Keywords: older adults, lung function, immunology, respiratory mechanics Introduction Since the 1950s the median age of the US population increased by 20 years. Increased life expectancy reflects, in part, a better understanding of the disease states, newer interventions, and the success of public health programs. The number of persons aged 65 and over is projected to increase from 35 million in 2000 to an estimated 71 million in 2030, with the largest increase in individuals age 80 and above (US Census 2005). Differentiating a disease state from “normal” aging is vital when encountering this population in the clinical setting. Respiratory system undergoes various structural, physiological, and immunological changes with age. There is a large variation in different physiologic measures among older adults, making it difficult to construct “normal” limits to differentiate a disease from a normal state. The current review explores age-related structural, physiological, and immunological changes of the respiratory system. These changes may in part explain older individuals’ clinical presentation and/or aberrant diagnostic studies, avoiding unnecessary interventions, and how these changes may predispose these vulnerable individuals to increased risk for respiratory diseases. Moreover, these changes may in part be responsible for variable response to currently available drugs to treat pulmonary diseases in older adults. Respiratory system mechanics The respiratory system comprises primarily the thoracic cage, lungs, and diaphragm. Total respiratory system compliance includes lung and chest wall compliance. Compliance is change in volume relative to change in pressure. Lung compliance Clinical Interventions in Aging 2006:1(3) 253–260 © 2006 Dove Medical Press Limited. All rights reserved 253