All of the following decrease with age EXCEPT:

With the aging process, there is a progressive loss of alveolar elastic recoil, costal cailage calcification, decreased interveebral space, and greater spinal curvature. These changes result in decline in lung function Decline in lung function with aging is indicated by a decrease in FEV1. This decrease is due to dynamic compression of airways. FRC increases with age. This is due to decreased elastic recoil and greater dynamic compression of airways. More amount of air is trapped in lungs at the end of expiration. Hence, option C is the answer. PO2 decreases with age. Decreased elastic recoil combined with dynamic compression results in early airway closure, mainly in the dependent airways. Hence, ventilation would be greater at the apex, the region which is normally less ventilated. It results in a VA/Q inequality, causing decreased PO2. Loss of alveolar surface area and reduced pulmonary blood flow would also lead to a decreased PO2. Reduced expansibility of lungs and weakened respiratory muscles would cause a decrease in TLC.