One critical issue in nNO measurement is to avoid contamination of nasal air by exhaled alveolar air during nNO sampling. This can be obtained by either breath holding, or by a breathing technique allowing soft palate closure during sampling, such as mouth breathing again resistance. However, as sampling times with the NIOX MINO are long (2 minutes at a flow of 2 ml/min, and 45 seconds at a flow of 5 ml/min), these techniques may be difficult to apply.