After smoking cessation, which benefit appears most immediately?

The immediate benefit of decreased carboxyhemoglobin concentration after smoking cessation is significant because carbon monoxide, a harmful component of cigarette smoke, binds to hemoglobin in the blood, reducing its ability to carry oxygen. When a person stops smoking, the levels of carbon monoxide in their system drop quickly, leading to an immediate increase in oxygen levels in the blood. This benefit can occur within just a few hours of smoking cessation, highlighting a rapid improvement in oxygen transport and overall respiratory function.

While decreased airway secretions, decreased airway reactivity, and decreased incidence of postoperative pneumonia are all important benefits associated with quitting smoking, they tend to manifest over a longer duration. Decreased airway secretions and airway reactivity can take days to weeks to improve as the respiratory system begins to heal, and the reduction in the risk of postoperative pneumonia typically becomes more apparent with longer-term cessation and improvement in lung health. Thus, the immediate physiological change following smoking cessation is most directly related to the rapid decrease in carboxyhemoglobin concentration, making it the correct answer.