[Efficacy of nasal O2 administration during mouth breathing]

27 subjects with healthy lungs received during conscious mouth breathing of room air simultaneously also nasally applied O2. The mean O2 concentration of the expiratory air at the mouth was a measure for the effective inspiratory oxygen concentration. Application through a nasal mask at 4 l/min O2 flow proved only slightly superior to the airtight nose frame (25.2 vs 23.6 per cent by volume O2), whereas the highest concentration was achieved by mask and reservoir (35.3 vol.%; 2P less than 0.001). The five habitual mouth breathers of the subject group did not show any O2 uptake through the nose in any of the experiments, the mean nasal share of the inspiration being calculated at 2.5% against 25% for the other subjects (2P less than 0.001). The interindividual differences proved independent of nose resistance and are ascribed to changing active positioning of the soft palate. This mechanism must be taken into consideration when assessing the arterial blood gases in oronasal respiration.