Susceptibility to carbon monoxide poisoning increases as

• A. Altitude increases
• B. Altitude decreases
• C. Temperature increases
• D. Humidity increases

Answer: (A)

When carbon monoxide is present, it binds to hemoglobin far more readily than oxygen, forming carboxyhemoglobin and preventing oxygen from attaching or being released to tissues. This reduces the blood’s oxygen-carrying capacity. At higher altitudes, the partial pressure of oxygen in the air is lower, so there’s less O2 available in the blood to begin with. With CO competing for the limited binding sites, the impact on usable oxygen becomes larger, making hypoxia develop more quickly and feel more severe. That’s why susceptibility to CO poisoning increases as altitude rises. Temperature or humidity don’t directly change CO’s binding to hemoglobin, and lowering altitude would improve oxygen availability, not worsen it.