A system for delivering a flow of breathing gas to a patient that includes a main delivery conduit coupled to a gas source, and a rotary coupling device coupled to the main delivery conduit and having a first member and a second member, the first member defining a first channel and a second channel through the first member, the second member defining a third channel and a fourth channel through the second member. The first channel is in communication with the third channel to define a main channel having a main path, and the second channel is in communication with the fourth channel to define a secondary channel separate from the main channel and having a secondary path. The first member and the second member are structured to freely rotate relative to one another in a manner that separately maintains the main path and the secondary path, characterized in that the first member (190) includes a first cylindrical body portion (196) that defines the first channel (202) and the second channel (204), the second channel having a first tube member (210) that extends from the first cylindrical body portion and a port (208) comprising an aperture in the first cylindrical body portion； and wherein the second member (192) includes a second cylindrical body portion (212) that defines the third channel (218) a second tube member (220) that extends from the second cylindrical body and defines the fourth channel, wherein the port is aligned with second tube member such that second channel is in sealed fluid communication with the second tube member.
