Physiological changes in respiratory function associated with ageing

Physiological ageing of the lung is associated with dilatation of alveoli, enlargement of airspaces, decrease in exchange surface area and loss of sup porting tissue for peripheral airways ("senile emphysema"), changes resulti ng in decreased static elastic recoil of the lung and increased residual vo lume and functional residual capacity. Compliance of the chest wall diminis hes, thereby increasing work of breathing when compared with younger subjec ts. Respiratory muscle strength also decreases with ageing, and is strongly correlated with nutritional status and cardiac index, Expiratory how rates decrease with a characteristic alteration in the flow-volume curve suggest ing small airway disease. The ventilation-perfusion ratio (V'A/Q') heteroge neity increases, with low V'A/Q' zones appearing as a result of premature c losing of dependent airways. Carbon monoxide transfer decreases with age, r eflecting mainly a loss of surface area. In spite of these changes, the res piratory system remains capable of maintaining adequate gas exchange at res t and during exertion during the entire lifespan, with only a slight decrea se in arterial oxygen tension, and no significant change in arterial carbon dioxide tension. Ageing tends to diminish the reserve of the respiratory s ystem in cases of acute disease. Decreased sensitivity of respiratory centr es to hypoxia or hypercapnia results in a diminished ventilatory response i n cases of heart failure, infection or aggravated airway obstruction, Furth ermore, decreased perception bronchoconstriction and diminished physical ac tivity may result in lesser awareness of the disease and delayed diagnosis.