Which respiratory hazard targets the heart and brain?

• A. Hydrogen cyanide
• B. Carbon monoxide
• C. Airborne pathogens
• D. Hydrogen chloride

Answer: (A)

Hydrogen cyanide disrupts the body's ability to use oxygen at the cellular level. It blocks a key enzyme in the mitochondria (cytochrome oxidase), so even if oxygen is available in the blood, cells cannot generate ATP. Tissues with high energy demands, especially the heart and brain, are the most sensitive to this disruption, so they are affected first and most severely. That direct interference with cellular respiration makes hydrogen cyanide particularly targeting to the heart and brain.

Carbon monoxide also harms these organs by reducing oxygen delivery (it binds hemoglobin more readily than oxygen), but its effect is through impaired transport rather than blocking how cells use oxygen. Airborne pathogens cause infection, and hydrogen chloride is primarily an irritant to airways, not a direct metabolic toxin to heart and brain.