The heart of a 19-year-old has none of the accumulated disease — the atherosclerosis, the valvular changes, the electrical conduction abnormalities — that makes older hearts more susceptible to the arrhythmias that hypothermia can trigger.

A young heart can be slowed to a very low rate and then gradually warmed back to normal rhythm in a way that an older, diseased heart might not manage.

Young people also have, on average, more physiological reserve than older people — a greater capacity to tolerate disruption to their normal function and recover from it.

The kidneys of a healthy 19-year-old can tolerate a period of severely reduced blood flow better than the kidneys of a 60-year-old with chronic kidney disease.

The liver of a young, healthy person can manage the metabolic consequences of hypothermia and rewarming more effectively than one that has been damaged by decades of illness or alcohol use.