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 (102) comprises a first cylindrical portion (106) and a second, wider cylindrical portion (108) coupled to and extending from the first cylindrical portion, the first cylindrical portion including a first inner cylindrical wall (112) and the second cylindrical portion including a first outer cylindrical wall (114) and a second inner cylindrical wall (116), wherein the first member further comprises a first port (120) that provides access to a space between the first outer cylindrical wall and the second inner cylindrical wall, wherein the first and second inner cylindrical walls define the first channel and the first port comprises part of the second channel； andwherein the second member (104) comprises a third cylindrical portion (122) and a fourth, narrower cylindrical portion (124) coupled to and extending from the third cylindrical portion, the third cylindrical portion including a second outer cylindrical wall (126) and a third inner cylindrical wall (128), wherein the second member further comprises a second port (132) that provides access to a space between the second outer cylindric
