Background: The concentration of nitric oxide (NO) measured from the nose is much higher than in the lower airways and increases during humming. We assessed nasal NO (nNO) normal values during breath hold and during humming in healthy adults. Materials and methods: Nasal NO concentrations were measured in healthy adults (ages 18-70). They held their breath for 10 s and thereafter hummed as loud as possible with their mouths closed also for 10 s. During breath hold, air was passively extracted from one nostril with 700 mL min -1. The average NO concentration at the plateau after 7-10 s was recorded and the mean of three consecutive measurements was calculated. During humming, air was extracted with 1200 mL min-1, the peak NO values were recorded. Results One hundred healthy adults participated (37 men). The nNO concentrations during breath hold were distributed normally (mean: 455 parts per billion (p.p.b.), SD 147). A random subgroup of 40 out of the 100 subjects (15 men) performed nNO measurement during humming. The median peak NO value was 1019 p.p.b. (SD 561) at the first, and 837 p.p.b. (SD 408) at the second measurement. There was a significant difference between the peak NO values of first and second humming. Conclusion: We present normal values for nNO in adults, which can be used to assess the value of nNO in respiratory illnesses. The peak nNO values during humming are variable, and their clinical relevance remains to be shown.

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European Journal of Clinical Investigation
Department of Otorhinolaryngology

Struben, V.M.D, Wieringa, M.H, Mantingh, C.J, Bruinsma, S.M, de Jongste, J.C, & Feenstra, L. (2005). Silent and humming nasal NO measurements in adults aged 18-70 years. European Journal of Clinical Investigation, 35(10), 653–657. doi:10.1111/j.1365-2362.2005.01559.x