A cannula having four separate flow passages, the cannula comprising: a nasal main body having first and second main flow chambers (102U, 104U) respectively communicating with first and second ports (108U, 110U), and the first and second flow chambers (102U, 104U) being separated from one another by a nasal septum; a mouth main body located adjacent the nasal main body and having a third flow chamber therein communicating with a third port; a first nare having a first nasal port and a first nasal flow chamber communicating with the first main flow chamber; a second nare having a second nasal port and a second nasal flow chamber communicating with the second main flow chamber; characterised by; the mouth main body being separated into third and fourth flow chambers (102L, 104L), separated from one another by a mouth septum, the fourth flow chamber being connected to a fourth port; a curved first mouthpiece extending from the mouth main body and having a first mouthpiece flow chamber communicating, at one end, with the third flow chamber and the third port; the free end of the first mouthpiece, remote from the third flow chamber defining a first mouth port; a curved second mouthpiece extending from the mouth main body and having a second mouthpiece flow chamber communicating, at one end, with the forth main flow chamber and the fourth port; the free end of the second mouthpiece, remote from the forth flow chamber defining a second mouth port; wherein a first flow path comprises the first port, the first main flow chamber, the first nasal flow chamber and the first nasal port; a second flow path comprises the second port, the second main flow chamber, the second nasal flow chamber and the second nasal port; a third flow path comprises the third port, the third flow chamber, the first mouthpiece flow chamber and the first mouth port; and a forth flow path comprises the forth port, the forth flow chamber, the second mouthpiece flow chamber and the second mouth port. a nasal main body having first and second main flow chambers (102U, 104U) respectively communicating with first and second ports (108U, 110U), and the first and second flow chambers (102U, 104U) being separated from one another by a nasal septum; a mouth main body located adjacent the nasal main body and having a third flow chamber therein communicating with a third port; a first nare having a first nasal port and a first nasal flow chamber communicating with the first main flow chamber; a second nare having a second nasal port and a second nasal flow chamber communicating with the second main flow chamber; characterised by; the mouth main body being separated into third and fourth flow chambers (102L, 104L), separated from one another by a mouth septum, the fourth flow chamber being connected to a fourth port; a curved first mouthpiece extending from the mouth main body and having a first mouthpiece flow chamber communicating, at one end, with the third flow chamber and the third port; the free end of the first mouthpiece, remote from the third flow chamber defining a first mouth port; a curved second mouthpiece extending from the mouth main body and having a second mouthpiece flow chamber communicating, at one end, with the forth main flow chamber and the fourth port; the free end of the second mouthpiece, remote from the forth flow chamber defining a second mouth port; wherein a first flow path comprises the first port, the first main flow chamber, the first nasal flow chamber and the first nasal port; a second flow path comprises the second port, the second main flow chamber, the second nasal flow chamber and the second nasal port; a third flow path comprises the third port, the third flow chamber, the first mouthpiece flow chamber and the first mouth port; and a forth flow path comprises the forth port, the forth flow chamber, the second mouthpiece flow chamber and the second mouth port.