1. A method for determining dynamically a respiratory feature in a spontaneously breathing patient receiving mechanical ventilatory assist, the method comprising: using a respiratory neural drive detector to measure a respiratory neural drive of the spontaneously breathing patient; using a neurally controlled ventilator to apply ventilatory assist pressure to the spontaneously breathing patient as a function of the respiratory neural drive of the spontaneously breathing patient; using a controller to modify a level of mechanical ventilatory assist applied to the spontaneously breathing patient by the neurally controlled ventilator until an airway pressure detector detects a change of gradient of a measured airway pressure of the spontaneously breathing patient, wherein the gradient represents a rate of change for the measured airway pressure in response to modifying the level of mechanical ventilatory assist; and determining, using a calculator, the respiratory feature of the spontaneously breathing patient based on the measured airway pressure upon detecting the change of gradient of the airway pressure.