Continuous positive airway pressure controller

A continuous positive airway pressure controller (1,40,60) for supplying a regulated oxygen/air mix to a respiratory circuit, the controller (1,40,60) comprising a main oxygen inlet port (4) for connecting to an oxygen supply source, a venturi mixing means (16) located in a venturi accommodating chamber (18) for blending oxygen and air to form the oxygen/air mix, a main jet means (14) communicating with the main oxygen inlet port (4) for delivering a primary oxygen supply through the venturi mixing means (16) for drawing air from the venturi accommodating chamber (18) into the venturi mixing means (16) for blending air with the primary oxygen to form the oxygen/air mix, an air inlet (19) to the venturi accommodation chamber (18) for communicating the venturi accommodating chamber (18) with ambient air, a secondary oxygen communicating means (27) communicates the venturi accommodating chamber (18) with the main oxygen inlet port (4) for delivering a secondary oxygen supply into the venturi accommodating chamber (18) for enriching the oxygen/air mix, and a main outlet port (5) from the venturi mixing means (16) for delivering the oxygen/air mix, characterised in that a secondary flow control means (28) is provided for regulating the flow of oxygen through the secondary oxygen communicating means (27) for varying the ratio of the oxygen to air of the oxygen/air mix delivered from the main outlet port (5), and a pressure regulating means (10) is provided for maintaining the pressure of the oxygen being delivered to the main jet means (14) and to the secondary flow control means (28) substantially similar, and for varying the flow rate of the oxygen/air mix delivered from the main outlet port (5) independently of the ratio of the oxygen to air of the oxygen/air mix.