This document presents the concept of Mechanical Ventilation, characteristics of the generator or mechanical ventilator and the different variables of ventilation control in volume, flow, pressure and time. In order to appreciate the changes of these variables, there is a simulation with ventilation control by pressure, taking as a model the pulmonary unicompartimental mathematical model to obtain the corresponding graphics. The simulation is made thanks to the use of a software developed in the MATLAB platform. It produces a bookstore named Simulink (use of blocks which determine the graphic exit with regard to the entry).