The invention is related to ventilation apparatuses and methods for operating a ventilator of a ventilator apparatus. In the method at least one duration ratio factor is set in a computing system of the ventilator apparatus; at least one minute volume, at least one functional dead space volume and at least one time constant are determined; a respiration frequency is computed, based on a previously defined lung model, depending on the determined parameters. The computed respiration frequency is optimized on at least one minimum of a delivered parameter, which is induced to a patient using the ventilator; an inspiratory time and an expiratory time are determined based on the computed respiration frequency and the duration ratio factor; at least one tidal volume based on the previously computed respiration frequency and the determined minute volume is computed; and a delivered respiratory parameter of the ventilator is closed loop controlled.