What factor is primarily responsible for decreased lung perfusion and diffusion in the elderly?

The primary factor responsible for decreased lung perfusion and diffusion in the elderly is increased physiological shunting. As individuals age, there are significant changes in the pulmonary system, including alterations in ventilation-perfusion relationships. Increased physiological shunting indicates that there is a portion of blood that bypasses oxygenation due to ventilation defects or mismatches, leading to a reduction in effective lung function.

In older adults, several physiological changes can contribute to an increased shunt. The decline in alveolar ventilation can occur due to various factors, including airway resistance and reduced lung compliance, which affects how well oxygen can diffuse from the alveoli into the blood. This inefficiency leads to an increase in right-to-left shunting, where blood flows from the right side of the heart to the left without being adequately oxygenated in the lungs.

The other choices do not adequately represent the primary factor. For instance, decreased elasticity of alveoli does play a role in lung function decline, but it does not specifically define the increased physiological shunt occurring in older adults. Increased forced expiratory volume in one second (FEV1) would suggest better lung function, which is contradictory to the struggles faced by the elderly. Decreased residual volume (RV) pressure is not typically a major factor