Abstract: A ventilator, including: a housing; a reservoir within the housing, wherein the reservoir has an internal chamber, an air inlet port, configured to place in fluid communication the internal chamber with atmospheric air, and an oxygen inlet port, configured to place in fluid communication the internal chamber with a source of oxygen; and a primary blower having an air inlet in fluid communication with the internal chamber, and an air outlet configured to be placed in fluid communication with an inspiration tube external of the ventilator housing, wherein the internal chamber presents a volume for gas mixing extending at least between the air inlet port, the oxygen inlet port and the primary blower air inlet, said volume configured for allowing mixing of air entering in the reservoir via the air inlet port with oxygen entering via the oxygen inlet port before any gas reaches the primary blower air inlet.