A breathing assistance apparatus comprising: a) a source of NO-containing gas, and b) a nasal cannula assembly in fluid communication with said source of NO-containing gas, the nasal cannula assembly adapted to deliver gases to a patient, wherein the nasal cannula assembly comprises: A) a hollow body configured to be capable of acting as a gas conduct or a gas manifold and comprising an internal chamber defining a first compartment, B) the first compartment and a second compartment separated by a separation wall, C) a pair of nasal prongs in fluid communication with the first compartment, D) the first compartment comprising a first inlet forming a side gases entry in fluid communication with a gas transport conduct and configured to conduct a first gas into said first compartment, E) the second compartment having a fully inflated internal volume for a gas, the second compartment comprising,. a second inlet configured to conduct a second gas into said second compartment, said second gas being NO-containing gas from the source of NO-containing gas, and. a deformable wall forming a part of the boundary between the second compartment and the room atmosphere, and wherein the separation wall comprises at least two flow restriction channels. a) a source of NO-containing gas, and b) a nasal cannula assembly in fluid communication with said source of NO-containing gas, the nasal cannula assembly adapted to deliver gases to a patient, wherein the nasal cannula assembly comprises: A) a hollow body configured to be capable of acting as a gas conduct or a gas manifold and comprising an internal chamber defining a first compartment, B) the first compartment and a second compartment separated by a separation wall, C) a pair of nasal prongs in fluid communication with the first compartment, D) the first compartment comprising a first inlet forming a side gases entry in fluid communication with a gas transport conduct and configured to conduct a first gas into said first compartment, E) the second compartment having a fully inflated internal volume for a gas, the second compartment comprising,. a second inlet configured to conduct a second gas into said second compartment, said second gas being NO-containing gas from the source of NO-containing gas, and. a deformable wall forming a part of the boundary between the second compartment and the room atmosphere, A) a hollow body configured to be capable of acting as a gas conduct or a gas manifold and comprising an internal chamber defining a first compartment, B) the first compartment and a second compartment separated by a separation wall, C) a pair of nasal prongs in fluid communication with the first compartment, D) the first compartment comprising a first inlet forming a side gases entry in fluid communication with a gas transport conduct and configured to conduct a first gas into said first compartment, E) the second compartment having a fully inflated internal volume for a gas, the second compartment comprising,. a second inlet configured to conduct a second gas into said second compartment, said second gas being NO-containing gas from the source of NO-containing gas, and. a deformable wall forming a part of the boundary between the second compartment and the room atmosphere,. a second inlet configured to conduct a second gas into said second compartment, said second gas being NO-containing gas from the source of NO-containing gas, and. a deformable wall forming a part of the boundary between the second compartment and the room atmosphere,