Which of the following is an age-related change in the respiratory system?

The age-related change in the respiratory system that is most relevant among the choices provided is a decrease in lung capacity. As individuals age, various physiological changes take place in the respiratory system that can affect lung function. These changes include a decrease in elastic recoil of the lung tissue, changes in the airway structure, and a reduction in the strength and effectiveness of respiratory muscles. Consequently, these factors lead to a diminished lung capacity, particularly affecting vital capacity and total lung capacity.

While cancer can be more prevalent in older individuals due to accumulated risks and exposures over time, it is not a direct change within the respiratory system itself, but rather a disease process that can affect people of all ages. In contrast, age-related changes such as decreased lung capacity are intrinsic to the aging process. Constricted airways and aortic stenosis are also not directly classified as normal age-related changes specific to the respiratory system; rather, they involve cardiovascular or other systemic concerns.