1. A ventilator system having patient connection means and a plurality of integrated modes of operation for providing a patient with a flow of breathing gas under pressure comprising valve means for controlling said flow of gas to said patient connection means for inspiration and expiration, mode selecting means for operating said ventilator system in at least one selected mode of operation; adjustable setting means including a plurality of adjustable time setting means individually related to sigh inspiratory time, sigh expiratory time, inspiratory time, expiratory time and inspiratory pause time each corresponding to said integrated modes of operation with each of said time setting means producing a corresponding time related threshold signal, signal means including time base means for producing a common time signal which increases in value with time at a predetermined linear slope for a predetermined time duration, means for comparing and determining the crossing of each threshold signal with said common time signal for producing a plurality of control signals, means responsive to said mode selecting means for selecting at least one control signal corresponding to a selected integrated mode and for resetting the time base means to begin a new time signal thereby to provide said predetermined time duration, and means for applying said at least one selected control signal to said valve means for controlling the flow of gas to said patient connection means whereby each of said time setting means may be continuously adjusted to change one or more of said threshold signals without varying any of the other threshold signals.