A ventilator (10) that pressurizes gas from a body of gas to provide a flow of gas to an airway of a subject (14) such that the gas flow mechanically facilitates the respiration of the subject (14). In order to enhance the comfort of the subject (14) during ventilation by the ventilator (10), the ventilator (10) enables the subject (14) to make unsupervised adjustments to one or more of the properties of the gas flow, within predetermined limits.