Aging results in several changes in breathing, many of which are a direct result of the mechanical changes in the respiratory system that occur with aging. Respiratory system compliance, lung compliance, and chest wall compliance all decrease, as does the strength of the inspiratory and expiratory muscles. As a result of these mechanical changes, functional residual capacity (FRC), residual volume (RV), and closing volume all increase, whereas the forced expiratory volume in one second (FEV1), forced vital capacity (FVC), and FEV1/FVC ratio all decrease. Aging also increases the collapsibility of the upper airway. The ventilatory response to hypoxia and hypercapnia is decreased in the elderly, along with decreased sensitivity to added elastic and resistive loads. Aging has several effects on gas exchange. Ventilation–perfusion inequality increases, with an accompanying increase in physiological dead space, a decrease in arterial partial pressure of oxygen (PO2), and an increase in the alveolar–arterial oxygen difference.