A ventilator apparatus comprising a ventilator with at least one actuator, further comprising; at least one computing system connected to said at least one actuator of the ventilator; at least one transducer (35, 36) configured to provide input signals from a patient to said computing system including at least one minute volume (Mv); wherein at least one processor of the computing system is configured to execute a program stored in a memory of the computing system, said program being configured to compute a respiration frequency (f) based on a previously defined lung model, depending on said minute volume (Mv), at least one stored functional dead space (Vd), at least one stored time constant (R*C) and at least one stored duration ratio factor (D1, D2), said computed respiration frequency (f) being optimized on at least one minimum of a delivered parameter (G_tot), and the program being further configured to estimate an inspiratory time (Ti) and an expiratory time (Te) based on said computed respiration frequency (f) and said at least one duration ratio factor (D1, D2), and to compute at least one tidal volume (Vt) based on said computed respiration frequency (f) and said determined minute volume (Mv); and a closed loop controller connected to said computing system, the closed loop controller configured to provide output data representing a delivered respiratory parameter of the ventilator, including at least one of a respiratory pressure (Rp), a respiratory volume (Rv) and a respiratory flow (Rf), based on said computed respiration frequency (f), said determined inspiratory time (Ti), said determined expiratory time (Te) and said computed tidal volume (Vt), and wherein the estimation of the inspiratory time (Ti) is limited by an extremum, preferably wherein the extremum depends on a maximum value computed with computing system as: max Ti max_ IBW, min Ti max, 3 ∗ R ∗ C, wherein Timax_IBW is a maximum inspiratory time based on the ideal body weight of the patient, Timax is a maximum inspiration time, and R*C is the time constant. at least one computing system connected to said at least one actuator of the ventilator; at least one transducer (35, 36) configured to provide input signals from a patient to said computing system including at least one minute volume (Mv); wherein at least one processor of the computing system is configured to execute a program stored in a memory of the computing system, said program being configured to compute a respiration frequency (f) based on a previously defined lung model, depending on said minute volume (Mv), at least one stored functional dead space (Vd), at least one stored time constant (R*C) and at least one stored duration ratio factor (D1, D2), said computed respiration frequency (f) being optimized on at least one minimum of a delivered parameter (G_tot), and the program being further configured to estimate an inspiratory time (Ti) and an expiratory time (Te) based on said computed respiration frequency (f) and said at least one duration ratio factor (D1, D2), and to compute at least one tidal volume (Vt) based on said computed respiration frequency (f) and said determined minute volume (Mv); and a closed loop controller connected to said computing system, the closed loop controller configured to provide output data representing a delivered respiratory parameter of the ventilator, including at least one of a respiratory pressure (Rp), a respiratory volume (Rv) and a respiratory flow (Rf), based on said computed respiration frequency (f), said determined inspiratory time (Ti), said determined expiratory time (Te) and said computed tidal volume (Vt), and wherein the estimation of the inspiratory time (Ti) is limited by an extremum, preferably wherein the extremum depends on a maximum value computed with computing system as: max Ti max_ IBW, min Ti max, 3 ∗ R ∗ C, wherein Timax_IBW is a maximum inspiratory time based on the ideal body weight of the patient, Timax is a maximum inspiration time, and R*C is the time constant.