A system for delivering a flow of breathing gas to a patient, comprising: a main delivery conduit coupled to a source of the flow of the breathing gas; a rotary coupling device coupled to the main delivery conduit, the rotary coupling device having a first member and a second member, the first member defining a first channel through the first member and a second channel through the first member, the second member defining a third channel through the second member and a fourth channel through the second member, wherein the first channel is in communication with the third channel to define a main channel having a main path through the rotary coupling device that is in communication with the main delivery conduit, wherein 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 through the rotary coupling device and wherein the first member and the second member are structured to freely rotate relative to one another for unlimited, 360° rotation about a longitudinal axis of the rotary coupling device in a manner that separately maintains the integrity of the main path and the secondary path, wherein the first member comprises a first cylindrical portion and a second, narrower cylindrical portion coupled to and extending from the first cylindrical portion, the first cylindrical portion including a first cylindrical wall and a second cylindrical wall, the second cylindrical wall defining the second channel, and a space between the first cylindrical wall and the second cylindrical wall defining the first channel; and in that the second member comprises a first end that is structured to sealingly and rotatably engage the second cylindrical portion of the first member, a main outer wall that defines the third channel, and an internal tube member that defines the fourth channel, characterized in that the internal tube member runs through the main outer wall such that a first end of the internal tube member extends out of the main outer wall. a main delivery conduit coupled to a source of the flow of the breathing gas; a rotary coupling device coupled to the main delivery conduit, the rotary coupling device having a first member and a second member, the first member defining a first channel through the first member and a second channel through the first member, the second member defining a third channel through the second member and a fourth channel through the second member, wherein the first channel is in communication with the third channel to define a main channel having a main path through the rotary coupling device that is in communication with the main delivery conduit, wherein 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 through the rotary coupling device and wherein the first member and the second member are structured to freely rotate relative to one another for unlimited, 360° rotation about a longitudinal axis of the rotary coupling device in a manner that separately maintains the integrity of the main path and the secondary path, wherein the first member comprises a first cylindrical portion and a second, narrower cylindrical portion coupled to and extending from the first cylindrical portion, the first cylindrical portion including a first cylindrical wall and a second cylindrical wall, the second cylindrical wall defining the second channel, and a space between the first cylindrical wall and the second cylindrical wall defining the first channel; and in that the second member comprises a first end that is structured to sealingly and rotatably engage the second cylindrical portion of the first member, a main outer wall that defines the third channel, and an internal tube member that defines the fourth channel, characterized in that the internal tube member runs through the main outer wall such that a first end of the internal tube member extends out of the main outer wall.