A team of doctors conducts potentially life-saving experiments in Horizon's 'death zone' This two-part special follows a team of doctors conducting a series of groundbreaking experiments as they climb Everest, the world's highest peak. From their laboratory tents, pitched in -25&degC conditions, the experts use their own bodies for medical tests. They push themselves to the limit to better understand the human body's behaviour in a low-oxygen environment. The team hopes their work will lead to new, life-saving treatments for intensive care patients suffering from hypoxia, a shortage of oxygen in the body.