Chemical asphyxiants other than carbon monoxide: hydrogen sulfide and cyanide. Hydrogen sulfide: the knockdown effect, cytochrome oxidase inhibition, carotid body stimulation and respiratory arrest, nitrite treatment, and long-term neurologic sequelae. Cyanide: cellular mechanism of toxicity, lactic acidosis and elevated venous oxygen saturation, retinal arterialization, antidotes (hydroxocobalamin, sodium thiosulfate, nitrites), fire-gas exposure, and the bitter almond odor.
During a medical evaluation for a suspected occupational cyanide exposure, one industrial hygienist detects a 'bitter almond' odor on the victim's breath, while the attending occupational physician cannot detect any such odor. Which of the following best explains this difference?