Preoxygenation optimizes oxygen content in the functional residual capacity (FRC). Adequate preoxygenation is defined by an expiratory oxygen fraction (FEO2) > 90%. Inspiratory support and positive end expiratory pressure (PEEP) can create a better reservoir, improve gas exchange and shorten the time needed for adequate preoxygenation. The goal of the study is to evaluate the efficacy and tolerability of different levels of inspiratory support and positive end expiratory pressure during preoxygenation in healthy subjects.