The aim of mechanical ventilation is to substitute physiological respiratory function. The boom of mechanical ventilation came during the XVIII century with the development of Reanimation Societies in Europe, who promoted the use of positive pressure ventilation modes. This type of ventilation caused new complications due to excessive positive pressure in the airway. Therefore, during the XIX century negative pressure ventilation predominated, which became essential during the second half of the 19th century and first half of the 20th century. Positive pressure ventilation was relegated to operating rooms until 1952, when it was imposed over negative pressure ventilation during the Copenhagen polio epidemic. Björn Ibsen contributed significantly to this change of ventilation paradigm, which led to the latest ventilation strategies and the development of the actual intensive care units.